31 results
Environment

Development and testing of a dynamic model for data from recreational fisheries

Project number: 2002-075
Project Status:
Completed
Budget expenditure: $112,210.00
Principal Investigator: Norman G. Hall
Organisation: Murdoch University
Project start/end date: 19 Oct 2002 - 30 Jun 2005
:

Need

Models are urgently required that will allow stock assessment for fisheries in which a significant component of the catch is taken by recreational fishers, where these models will rely on abundance indices from the commercial fishery, occasional length or age composition samples from the total catch and occasional estimates of total catch. Given the expense associated with recreational surveys, there is a need for the development of an approach that would allow determination of an appropriate frequency for such creel censuses in order that they might provide the data necessary to achieve a specified level of precision from the resulting stock assessment. A method is required that will allow an assessment of the value of data derived from commercial fisheries statistics for use in assessing the stocks that are shared by recreational and commercial fishers, prior to making final management decisions on catch re-allocation from the commercial to the recreational fishing sector.

Objectives

1. To develop a dynamic fishery model that uses those types of data, which are typically available for recreational fisheries.
2. To assess the suitability of the model in providing a tool that fisheries agencies might use to investigate the trade-off between the cost and the resultant benefit for stock assessment associated with different frequencies of such surveys.
3. To assess the suitability of the model in providing an approach that might be used by fisheries agencies to investigate the consequences for subsequent stock assessment of reducing the proportion of the catch that is allocated to the commercial fishing sector.
Environment

Biological data for the management of competing commercial and recreational fisheries for King George whiting and black bream

Project number: 1993-082
Project Status:
Completed
Budget expenditure: $115,674.00
Principal Investigator: Ian Potter
Organisation: Murdoch University
Project start/end date: 11 Aug 1993 - 19 Feb 1997
:

Objectives

1. To produce detailed biological and mesh selectivity data to enable the WA Fisheries Department to determine sustainable and optimum yields for king george whiting and black bream
2. Objectives as stated in B3 part B of the project Description forming part of this agreement

Final report

Authors: I.C. Potter G.A. Hyndes M.E. Platell G.A. Sarre F.J. Valesini G.C. Young D.J. Tiivel
Final Report • 1996-09-01 • 10.53 MB
1993-082-DLD.pdf

Summary

Both the King George whiting and the Black bream are important commercial and recreational finfish species in south-western Australia. The fisheries for Black bream are restricted to estuaries, whereas the King George whiting recreational fisheries is based in both estuaries and protected marine waters. Due to the increase in catches of King George whiting and Black bream, the Western Australian Fisheries Department required research to develop management policies that will benefit both the commercial and recreational fishers who target these two species. The main biological information needed was the growth rate, maximum age, age and length at sexual maturity, spawning period and location, habitat requirements and the selectivity of gill net meshes for these species in south-western Australia.

The importance to commercial and recreational fish species of the various habitats found in the nearshore marine waters and estuaries of south-western Australia

Project number: 2000-159
Project Status:
Completed
Budget expenditure: $277,687.00
Principal Investigator: Ian Potter
Organisation: Murdoch University
Project start/end date: 10 Sep 2000 - 9 Oct 2004
:

Need

The urgent need for reliable quantitative data on the habitats which are used extensively by commercial and recreational fish species during one or more stages in their life cycles has been highlighted by Cappo et al. (1998) in their report to FRDC (95/055). That report identified a deficiency in a knowledge of the following:

1. Characteristics and locations of important fisheries habitats at scales useful for research and management.
2. Life history information for fish species, related to the types of habitats occupied throughout their life cycles, and data on the densities and/or biomass of those other biotic components of fish habitats, which provide food and/or protection for fish, such as invertebrates and aquatic vegetation.
3. Habitat dynamics and ecosystem processes, including food webs, habitat use and fisheries production in soft sediment substrata, such as beaches.
4. Fisheries-habitat links, including the influences of hydrodynamic and other processes on the recruitment of commercial and recreational fish species.

The above gaps in our knowledge were also highlighted by the FRDC in its “Research Priorities for Fisheries Ecosystem Protection”, when they listed two of its strategic R&D areas as “defining major habitats in the coastal exclusive economic zone” and “the roles of habitats in maintaining healthy fisheries production, ecosystem integrity and biodiversity”.

There is a particularly urgent need to fill the above gaps because the coastal and estuarine waters of Australia are becoming increasingly exposed to the effects of numerous coastal developments, e.g. the construction of harbours, marinas and groynes, and to the destruction of habitat through other forms of activity, e.g. dredging for sand and extreme forms of eutrophication. Information on which habitats are most important to commercial and recreational fish species in these waters are required by managers so that they can introduce appropriate plans for managing and conserving those habitats.

Objectives

1. Define quantitatively the range of habitat types found in nearshore marine and estuarine waters in south-western Australia.
2. Determine the compositions of the benthic macroinvertebrate faunas at sites representing the different habitat types and ascertain the extent to which such data help refine the criteria for defining the different habitat types.
3. Determine the compositions of the fish faunas in representative examples of the different habitat types, and thereby determine which habitats are "preferred" by each of the main commercial and recreational fish species.
4. Develop a suite of characteristics which can thus be used to predict which fish species will be found in each of the different types of habitat.
5. Determine, for a moderately sheltered and a moderately exposed coastal habitat, and a habitat in the Swan Estuary, the abundance, biomass and size composition of the main components of the diets of fish species and of the potential prey of those species in the benthos and water column. These data will be used to determine the most important prey for each of the abundant fish species and to construct a preliminary food web.
6. Collate the key components of the data collected by this study in a form that will enable fisheries and environmental managers to ensure that those areas of the coast that provide crucial habitats for important fish species are protected from deleterious anthropogenic activities.

Final report

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
:

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.
 
Communities
PROJECT NUMBER • 2016-034
PROJECT STATUS:
COMPLETED

Golden fish: evaluating and optimising the biological, social and economic returns of small-scale fisheries

This project investigates recreational and commercial fisher motivations for using a fishery and the beliefs, attitudes and perceived benefits of aquaculture-based enhancement programs and other management options. It also determines the total economic value for recreational fishing for Blue Swimmer...
ORGANISATION:
Murdoch University
Industry
PROJECT NUMBER • 2013-221
PROJECT STATUS:
COMPLETED

Stock enhancement of the Western School Prawn (Metapenaeus dalli) in the Swan-Canning Estuary; evaluating recruitment limitation, environment and release strategies

Keywords: Aquaculture-based enhancement, recreational fishing, restocking, post-release survival, larval ecology, larval taxonomy, fish predation Executive Summary: This report provides the first comprehensive investigation into the biology and ecology of the Western School Prawn...
ORGANISATION:
Murdoch University
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