122,526 results

Evaluation of methods of obtaining annual catch estimates for individual Victorian bay and inlet recreational fisheries

Project number: 2003-047
Project Status:
Completed
Budget expenditure: $380,064.00
Principal Investigator: Karina Ryan
Organisation: Agriculture Victoria
Project start/end date: 12 Jul 2003 - 31 Mar 2008
Contact:
FRDC
TAGS
Survey
Stakeholder
Recreational Fishing
Fisheries Management
Behaviour

Need

There are four related needs that would be addressed by the proposed project:
1. Assessments that require annual estimates of the recreational fishery as well as the commercial fishery
2. Resource allocation decisions
3. Development, implementation and review of fishery management plans
4. Matching the spatial resolution of recreational fishing data to the spatial scale at which fisheries are managed.

1. Estimates of total catch are of fundamental importance for undertaking stock assessments. The need for such data is frequently identified in fishery and stock assessments for Victorian Bay and Inlet Fisheries. The total catch by the recreational sector of some key species, such as snapper, whiting and bream, may be similar to or even exceed that by the commercial sector, but annual estimates of angler catches are difficult to obtain. The recently completed NRIFS has provided estimates of total catch for each State and for the Nation as a whole. However, these data have been collected at a broader spatial scale than that at which fish stocks and fisheries are usually assessed and managed. The exercise is unlikely to be repeated at less than 5 year intervals because of the expense and time involved. Methods need to be developed that allow such data to be collected from Victoria’s recreational fisheries on an annual basis, in a cost-effective manner, and at an appropriate spatial scale.

2. Resource allocation issues between the commercial and recreational fishing sectors are of increasing importance for fisheries managers. Victoria is likely soon to implement a formal resource allocation process for key bay and inlet fish resources that will require on-going estimates of total catch by each fishing sector to determine whether or not catch sharing targets are being met. The ability to set appropriate targets for particular fish resources is currently hampered by a lack of information on total catches by the recreational sector.

3. Development of ESD-based fishery management plans for Victoria’s bay and inlet fisheries is about to commence, adding a further important management context to the provision of estimates of total catch by the recreational sector. Having current information on the extent and dynamics of the recreational sector will be important in the development, implementation and review of these management plans.

4. The NRIFS will provide a very useful State-wide snapshot of recreational fishing catches, but its findings will become increasingly outdated. The assessment and management of individual fisheries in Victoria is also usually undertaken at a finer spatial scale than that provided by the NRIFS. Although the National survey may be repeated in several years there is a need for ongoing annual estimates of total recreational catch of key species that provides data at the spatial scale at which assessment and most management occurs. The breadth and complexity of the NRIFS, and its novelty, have contributed to the extended time period needed for analysis and reporting of results (over 16 months). This is understandable and probably acceptable for a large scale survey that is unlikely to be repeated more than once every 5 years, but is less useful for stock assessment purposes where more frequent and even annual reviews are desirable.

The experience with the NRIFS, and similar methods used in New Zealand, indicates that the method is potentially extremely useful. However, its applicability to smaller spatial scales and as an ongoing survey technique remains to be tested. Regardless of which method (or combination of methods) is chosen as the most appropriate for Victoria, it is always important to trial a new survey design before it is implemented (Pollock et al. 1994).

How the proposed project would meet these needs is further outlined in B6 – Planned Outcomes.

Objectives

1. Review survey methods used in the past to estimate total annual catches of key species in Victorian marine and estuarine recreational fisheries.
2. From the results of past surveys statistically assess the costs and sampling requirements of different survey methods for providing unbiased estimates of total recreational catch and effort, with acceptable precision
3. Conduct a workshop to evaluate alternative survey methods for estimating total recreational fishing catch and effort.
4. Develop a cost-effective survey design that would, if possible, provide annual estimates of total recreational catch for key species in the main bay and inlet recreational fisheries
5. Trial the recommended design.
6. Review the success of the pilot survey at a second workshop and recommend a final survey design.

Final report

ISBN: 9.78E+12
Author: Karina Ryan
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Final Report • 2010-02-01 • 3.82 MB
2003-047-DLD.pdf
Environment
PROJECT NUMBER • 2003-046
PROJECT STATUS:
COMPLETED

Reducing uncertainty in the assessment of the Australian spanner crab fishery

Spanner crabs (Ranina ranina) represent a valuable single-species fishery in Queensland. Although a transparent and effective assessment process was developed some years ago for setting the commercial total allowable catch (TAC), additional information was needed to reduce some of the uncertainty in...
ORGANISATION:
Department of Primary Industries (QLD)
TAGS
Survey
Physiology
Biotechnology
Aquaculture
Analytics
SPECIES
Spanner Crab
Environment
PROJECT NUMBER • 2003-045
PROJECT STATUS:
COMPLETED

Stock discrimination of blue-eye trevalla (Hyperglyphe antarctica) from Australian shelf waters and offshore seamounts and New Zealand

This work is principally about identifying the best method for examining the population structure of blue-eye trevalla (Hyperoglyphe antarctica). It is not, and was never intended to be, an exhaustive assessment of stock structure of blue-eye trevalla in Australia’s Fishing Zone. As such,...
ORGANISATION:
Agriculture Victoria
TAGS
Stock Assessment
Laboratory Procedures
Fisheries Management
Analytics
Ageing
SPECIES
Blue-Eye Trevallas
Environment
PROJECT NUMBER • 2003-044
PROJECT STATUS:
COMPLETED

Development of a sustainable industry-based observation system for blue grenadier at the primary spawning sites

Blue grenadier has the highest current TAC among SEF species and has two separate fisheries that target primarily either sub-adult fish year-round or mature adults in winter spawning aggregations. The sustainability of the fishery would be greatly enhanced with regular (sustained) monitoring of...
ORGANISATION:
CSIRO Oceans and Atmosphere Hobart
TAGS
Survey
Reproduction
Physiology
Fishing Effort
Electronic Monitoring
SPECIES
Blue Grenadier

Development of a robust suite of stock status indicators for the Southern and Western and the Eastern Tuna and Billfish fisheries

Project number: 2003-042
Project Status:
Completed
Budget expenditure: $402,291.00
Principal Investigator: Marinelle Basson
Organisation: CSIRO Oceans and Atmosphere Hobart
Project start/end date: 29 Jun 2003 - 30 Jun 2008
Contact:
FRDC
TAGS
Stock Assessment
Reproduction
Harvest Strategy
Fishing Effort
Fisheries Management

Need

Significant process is being made with existing projects focusing on the Eastern Tuna and Billfish fisheries (ETBF), but the need to develop and test suites of stock indicators with associated reference points and decision rules for use by the FAGs for each fishery remains, particularly for the Southern and Western region (SWTBF). The need is also urgent, given the imminent introduction of TAE/TAC based management plans and the need to formally evaluate them on an annual basis.

Given the potential difficulties and limitations of using only CPUE as an indicator of stock status there is a need to also consider other indicators, e.g. ones which might reflect local depletion, an issue which is of real concern. Standardisation of such indicators also needs to be considered. Different indicators (e.g. CPUE or mean length in the catch) reflect different aspects of the population dynamics, and there is increasing recognition of the value of considering a suite of indicators rather than relying on a single one. There are currently only limited and relatively unsophisticated frameworks for combining information from several indicators. There is a need to develop this further, and to design defensible and robust frameworks to use in management decision-making. There is also a need to test the robustness of suites of indicators within the context of a feed-back management loop rather than simply in a non-feedback sense.

Although this work is needed for, and will focus on the management of the domestic fisheries, there is an international need for this research. Tunas and billfish harvested in the SWTBF form part of the Indian Ocean stocks which fall under the remit of the Indian Ocean Tuna Commission (IOTC). The research proposed here was identified as a high priority task at recent IOTC Working party meetings.

Objectives

1. Design a candidate set of potential stock status indicators (SSIs) which reflect a wide range of aspects of stock and fishery status, and develop appropriate standardisation procedures for the SSIs
2. Modify existing operating models to reflect fish population and fishery dynamics of each relevant case study with particular focus on stock structure uncertainty
3. Develop candidate frameworks and methodology for a management system based on a suite of indicators
4. Test the robustness of SSIs (individually and jointly in framework) relative to arbitrary 'trigger' or reference points without built-in decision rules
5. Develop meaningful reference points, in consultation with FAGs, and test best-performing SSIs with built-in decision rules
6. Provide Southern and Western Tuna MAC, Eastern Tuna MAC and AFMA with an evaluation of the robustness of alternative SSI's in the context of management strategies

Final report

ISBN: 9.78E+12
Author: Marinelle Basson
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf
Final Report • 2008-09-12 • 7.91 MB
2003-042-DLD.pdf

Estimation of natural and fishing mortality using length composition data

Project number: 2003-041
Project Status:
Completed
Budget expenditure: $318,426.18
Principal Investigator: Norman G. Hall
Organisation: Murdoch University
Project start/end date: 28 Sep 2003 - 1 Sep 2008
Contact:
FRDC
TAGS
Stock Assessment
Mortality
Modelling
Data
Biomass

Need

Sound estimates of natural and fishing mortality form the basis of fishery stock assessment and modelling. Without these data, the extent to which the spawning biomass has been reduced or the effectiveness of management measures in sustaining wild fish stocks cannot be determined. These estimates of mortality are crucial if the commonly-used reference points for fishing mortality and biomass are to be used in managing fisheries. Considerable advances have been made in obtaining estimates of mortality when data on the age composition of the annual catch are available. However, when there are only data on the length composition of the catches, analyses become more complex and the algorithms are not as well defined. Although information is usually available within the biological and fishery data that allows estimation of total mortality, the information on natural mortality must usually be obtained from empirical models that relate natural mortality to characteristics of the life history for other fish species or by estimating the relationship between total mortality and fishing effort, thereby obtaining an estimate of natural mortality by subtraction. Furthermore, there is a need to understand how natural mortality varies with size. Although the study of mortality deserves to be a primary focus of fishery research, it is difficult and thus often set aside. For many of Australia’s finfish stocks, there is a need to develop length-based methods to estimate mortality, which can be used to monitor the stock status of the recreational fisheries, and to obtain improved estimates of natural mortality that can be used in assessing sustainability. The project falls within FRDC’s Natural Resources Sustainability Program and is intended to increase and apply knowledge of stock assessment methods by developing methods of estimating mortality using length composition data which, compared with age composition data, are relatively inexpensive to collect.

Objectives

1. To develop methods for estimating natural, fishing and total mortality from length composition data and, in particular, to enable the following objectives to be achieved.
2. To estimate total mortality by applying Length Frequency Analysis (LFA) methods to length composition data.
3. To estimate total mortality by applying a length-based method of relative abundance analysis to length composition data from consecutive years.
4. To estimate natural mortality from the changes in length composition data that accompany a change in minimum legal length.
5. To estimate natural mortality using a length-based fishery model
6. To determine whether these length-based methods can be used to estimate a size-dependent (rather than constant) natural mortality.

Final report

ISBN: 978-0-86905-988-3
Author: Norm Hall
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 
Final Report • 2017-09-29
2003-041-DLD.pdf

Summary

The objectives of this project were to develop length-based approaches for estimation of natural, fishing and total mortality, and to explore the application of these methods to the data from selected fisheries. The methods that were developed were essentially length-based versions of age-based approaches that are typically applied for stock assessment when appropriate and when representative age samples are available from either research or catch sampling. 
 
The study explored several methods to estimate mortality from length samples.  The simpler of these approaches assume that, as fishing mortality increases, fewer fish will survive to reach larger sizes.  Accordingly, the size composition becomes increasingly truncated at the right when fishing mortality increases.  Length FrequencyAnalysis and length-based catch curve analysis assess the extent to which the shape of the right-hand tail of the size distribution is reduced, and taking growth into account, use this information to estimate total mortality. The problem becomes more complicated, however, when annual recruitment varies. Relative Abundance Analysis attempts to track peaks and troughs in the length compositions in successive years, thereby identifying strong and weak year classes. By taking year class strength into account, the decline in the right-hand tail of the length distribution can be assessed more reliably, thereby improving the accuracy of the estimate of total mortality. An increase in minimum legal size allows smaller fish that would previously have been caught to survive and grow to the new minimum size.  If there are adequate data and the change in minimum size is sufficiently great, the change in the length compositions before and after the change in minimum size can be used to estimate the natural mortality. Finally, by analyzing the combined set of time series of fishery data, length and age samples, and attempting to track year classes through the catch-per-unit-of-effort, age-composition and length-composition data in successive years, it is possible to obtain estimates of both natural and fishing mortality. The precision of the estimates is dependent of the information content of the data, however.  This last analysis was extended to assess whether, for Tailor, there was evidence of length-dependent natural mortality.
 
The methods and software developed in this project were applied to length data for the Western Yellowfin Bream in Shark Bay, Tarwhine, Breaksea Cod, Dhufish, Snapper from NSW, Mud Crabs, King George Whiting, and Tailor.  The data for King George Whiting and Mud Crabs were found to be inappropriate for analysis using the approaches developed in this study. Although catch curve and relative abundance analysis produced highly inconsistent estimates of mortality for Breaksea Cod, reasonable and realistic estimates of mortality were produced for the other species. For Tailor, it was found that the assumption of constant natural mortality  resulted in a better fit of the fishery model than that which was obtained by using the length-dependent natural mortality assumption.
 
The analyses that were undertaken in this study demonstrated that the length-based approaches, while less precise and reliable than age-based methods, had potential for use in stock assessment. This is particularly the case for recreational fisheries, for which length samples are likely to be more readily available than age samples.
 

Dynamic modelling of socio-economic benefits of resource allocation between commercial and recreational use

Project number: 2003-039
Project Status:
Completed
Budget expenditure: $154,200.00
Principal Investigator: John Nicholls
Organisation: Data Analysis Australia (DAA)
Project start/end date: 29 Jun 2003 - 8 Sep 2006
Contact:
FRDC
TAGS
Recreational Fishing
Modelling
Fishing Effort
Economic

Need

Fisheries management (and stakeholders) at both State and national level do not have a well defined and documented framework and tested tool that is capable of modeling the way that changes in key variables impact on commercial and recreational relative use values over time and how this in turn affects socially optimum allocations through time. As a consequence,fisheries management is not well placed to be confident that decisions taken today are consistent with long term socially optimal outcomes.

In looking for a framework and set of tools to evaluate resource allocation options and to measure socially optimal allocations for the purposes of satisfying legislative, including ESD, objectives, decision makers have expressed a need for:
(1) a more general dynamic framework to look at optimal resource allocation through time .
(2) a socio-economic analytical framework with a consistent methodology and additional set of tested tools that explicitly take into account variables impacting on the optimization of socio-economic benefits from commercial and recreational uses through time;
(3) practical guidance in the application of the dynamic framework and advanced methodologies to address inter-sectoral related resource-sharing issues over time; and
(4) additional supporting methodologies and tools for WA Fisheries Department (and other fisheries Agencies throughout Australia) to use in the development of an integrated coastal fisheries management initiative that will provide a consistent framework for socio-economic analysis in addressing inter-sectoral resource allocation options over time.

Objectives

1. The development of a general framework that provides a theoretical basis for identifying key variables that impact on commercial and recreational use values over time
2. The documentation of a robust dynamic model capturing the significant variables that impact on these values over time and how these impact on socially optimum resource allocation through time and which allow simulations of the optimal resource allocations over time.
3. The demonstration of the application of the dynamic framework and model through three case studies associated with the current FRDC supported socio-economic valuation project (2001/065). This will advance the outputs from project 2001/065 in a logical, consistent and stepwise way

Final report

ISBN: 0-9756020-3-9
Author: John Nicholls
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Final Report • 2006-10-17 • 1.53 MB
2003-039-DLD.pdf

Summary

Fisheries-related resources are finite and the need to share these resources among competing uses is inevitable. These resource sharing issues can be extremely contentious, politically difficult, and are often a significant drain on fisheries management agencies’ and stakeholders’ limited resources. Hence, there needs to be a consistently sound and rational basis for assessing these allocation issues that is widely understood and generally acceptable as fair and reasonable.
 
Socio-economic valuation tools are recognized as a key component of ecological sustainable development (ESD) assessments of our natural resources. Recent projects, including two previous FRDC-sponsored projects, describe both the appropriateness of such analyses and the need for their use.
 
The research in this project presents a dynamic model based on economic principles that can be used to evaluate the likely future direction of the socially optimal inter-sectoral resource allocations over time. The research illustrates the application of the model in three Western Australian case study fisheries. These case studies illustrate the nature of the data used to implement the model, the method of analyzing that data and the determination of the optimal allocation path over time using these data and relationships.
Environment
PROJECT NUMBER • 2003-034
PROJECT STATUS:
COMPLETED

An ecological approach to re-establishing Australian freshwater cod populations: an application to trout cod in the Murrumbidgee catchment

This project consisted of two field experiments primarily designed to determine if dispersal of post-juvenile trout cod, Maccullochella macquariensis, is responsible for the apparent lack of success following stocking of this species into numerous riverine sites. The study also served to trial the...
ORGANISATION:
Environment ACT
TAGS
Stock Assessment
Remote Sensing
Population Dynamics
Modelling
Fishing Technology
SPECIES
Murray Cods
Industry
PROJECT NUMBER • 2003-033
PROJECT STATUS:
COMPLETED

Enhancement of saucer scallops (Amusium balloti) in Queensland and Western Australia - genetic considerations

The saucer scallop, Amusium balloti, is distributed along the Western and Eastern coast of Australia and supports a fishery in both Queensland and Western Australia. Two commercial companies are investing in sea-ranching operations in an attempt to stabilise and increase annual catches. These...
ORGANISATION:
Department of Primary Industries (QLD)
TAGS
Restocking
Genomics
Fisheries Management
Aquaculture
Analytics
SPECIES
Ballot's Saucer Scallop

Evaluating the recreational marron fishery against environmental change and human interactions

Project number: 2003-027
Project Status:
Completed
Budget expenditure: $315,953.00
Principal Investigator: Martin de Graaf
Organisation: Department of Primary Industries and Regional Development (DPIRD) WA
Project start/end date: 29 Jun 2003 - 29 Aug 2008
Contact:
FRDC
TAGS
Survey
Stock Assessment
Reproduction
Recreational Fishing
Nutrition
SPECIES
Marron

Need

Both the catch and range of marron have reduced over the last 25 years. A re-evaluation of the range will provide both the current extent and potential of the recreational marron fishery (RMF) and allow a re-interpretation of current production of the RMF.

Selecting two indicator sites will allow the focusing of research effort to achieve a new, useful level of detail on fecundity, recruitment and survival in indicator stocks, develop new performance measures and new models of productivity (stock recruitment and yield-per-recruit models). Although focused on indicator stocks, this will produce generic tools applicable to other marron stocks, providing a suite of powerful management indicators.

Changes in legal gears have occurred and these gears are likely to have different efficiencies and may explain a proportion of the decline in marron catches. By quantifying the relative efficiencies of the three legal gears, the historical data set can be re-evaluated to allocate a proportion of the decline in catches to changes in gears and predictions of the impact of future gear restrictions.

Identifying and ranking sources of marron mortality will provide key information on marron survival at various life-stages and allow management to focus resources on important mortality sources.

Environmental variables and management of catchments and water resources profoundly influence the extent and productivity of the entire RMF. The collection of data and development of models will provide fishery managers to identify key influences and engage with other management agencies to promote a more sustainable and productive RMF.

Objectives

1. To assess the present range of the recreational marron fishery (RMF) and compare to the historical range to quantify the reduction in marron range and current extent of the fishery.
2. To assess fecundity, recruitment and survival of marron in indicator sites to develop performance measures and models of productivity.
3. To quantify the relative efficiency of the three permitted capture methods at indicator sites and use the results to standardise the historical catch and effort database.
4. To identify and rank sources of mortality of marron at indicator sites.
5. To model the impact and effect of key environmental variables on marron stocks within the indicator sites and the RMF as part of the overall understanding of the decline in the fishery.
6. Piloting the qualitative assessment of mortality sources of a selected marron population.
7. Piloting the identification of the impacts of major environmental variables affecting a selected marron population.

Final report

ISBN: 1 921258 94 2
Author: Martin de Graaf
Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

Final Report • 2011-11-24 • 5.51 MB
2003-027-DLD.pdf

Summary

The distribution of marron in the southwest of Australia has seen many changes since European settlement. Reconstructions of their range from historical records suggested that marron inhabited the waters between the Harvey River and Denmark River. Due to translocation, their range has expanded as far north as the Hutt River and as far east as Esperance. Although at present marron still exist in all the original rivers within the southwest, their distribution within these rivers has contracted. Poor water quality, salinity, low rainfall and environmental degradation in the upper and lower reaches have restricted marron populations.

Historically, management decisions in the Recreational Marron Fishery have been based on fishery-dependent CPUE data collected using a logbook survey and phone survey. A critical assumption has been that the fisheries-dependent CPUE values were proportional to abundance. However, raw or nominal fisheries-dependent CPUE effort data are seldom proportional to abundance and relative abundances indices based on nominal and even standardised CPUE data are notoriously problematic and often provide little useful guidance for management. Although, the fishery-dependent programs provide high quality data on changes in the fishery, in isolation, these data provided limited information on the effects of fishing and the impact of fishery regulations on marron abundance. Standardising the fishery-dependent CPUE data for just one (introduction of snare-only areas during the 1990s) of the numerous management changes illustrated the significant bias in raw, nominal CPUE data. The use of biased fishery dependent data as measures for Recreational Marron Fishery productivity was probably one of the contributing factors limiting the success of developing predictive models using non-fishery variables (e.g. rainfall, river flow).

After a thorough review of (historical) sampling methods, a new fishery-independent annual research program using inexpensive box traps was implemented in 2006. Trapping allowed technical staff to sample several sites (2-4) simultaneously instead of just one site per night. More importantly, traps were set late afternoon and retrieved the following morning, removing the serious occupational health and safety issues associated with the historical late night (18:00- 1:00) sampling trips using drop nets and scoop nets. Furthermore, trapping removed the high level of subjectivity (e.g. operator skill level) associated with the traditional methods, especially scoop netting. Trap data appeared to be the most suitable as an index of relative abundance of marron. Interestingly, comparing trap catches with density data obtained through visual surveys using scuba revealed that at least over soft substrate in dams, trap catches can be used as both a measure of relative and absolute (#/m2) abundance.

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