Developing a fishery independent estimate of biomass for snapper
Cephalopod beak identification and biomass estimation techniques: tools for dietary studies of southern Australian finfishes
Final report
A table provides details of the species examined, classified to order and family, with information on the size and weight range of whole animals. Most complete beaks can be easily identified to the order level and a key is provided for this. Further keys are provided to allow identification to genus/species level within each of the four orders. Detailed descriptions of beaks are provided for each species, supplemented by further tables providing ranges, ratios and means of various beak characters.
A desk-top evaluation of the application of towed-body LIDAR to biomass assessment of demersal fish stocks
Assessment of broad-scale exploitation rates and biomass estimates for the Tasmanian southern rock lobster fishery
Traditionally, catch per unit of effort (CPUE) is used to monitor the health of the fishery and indicate the success or otherwise of management practices. Under current input controls CPUE is based on fishers maximising their total catch. In contrast, under output controls where catch is predetermined fishers will alter their catching scenarios to maximise the return (dollars per kilogram) from their catch. In southern rock lobster fisheries there is significant potential to alter fishing patterns to maximise economic return, especially through seasonal shifts in effort. As this change occurs, the value of using CPUE data to continue monitoring the fishery will be eroded. As such, both fisheries independant means of monitoring the fishery and new monitoring methods will become increasing important.
Both exploitation rates and biomass estimates are important stock assessment parameters and biological reference points in sustainable management of fisheries resources.
This project will evaluate fishery independant means of deriving these estimates and by determining the precision of derived estimates, demonstrate their suitability as biological reference points.
In a report to the Department of Industry, Technology and Commerce titled "Oceans of Wealth?", the Review Committee on Marine Industries, Science and Technology stated in their conclusion, 'The knowledge gained from scientific research into fish stocks and the impacts of the environmental and harvesting factors is a necessary but not sufficient element in the conservation of productive fish stocks. A vital element in both scientific assessments is the availability of reliable information about exploitation levels'. This project is aimed at addressing this need for southern rock lobster.
Final report
Exploitation rate is an important fishery assessment parameter linking catch to legal-sized biomass, the portion of the stock available for harvest. Relative change in legal-sized biomass is a crucial performance indicator for the fishery as it measures the success of management outcomes. Under the recently introduced Individual Transferable Quota Management System (ITQMS) in the Tasmanian rock lobster fishery, rebuilding of legal-sized biomass is a key management objective. The assessment model that produces biomass estimates for this fishery is primarily dependent on commercial catch and effort data.
The use of commercial catch and effort data for stock assessment relies on its de facto relationship with stock abundance. However, the relationship between catch and effort data and abundance is not always constant or linear. Improvements in fishing gear and technology can result in greater catch for a given amount of effort, unrelated to changes in the biomass. Management changes and fishers’ behaviour can also affect the relationship between catch rates and biomass. Under the new ITQMS introduced in 1998, catch is fixed and improved profits can be made by improving the return per unit of fish caught rather than by increasing the amount of catch through increased effort. Thus fishing during periods when catch rates are low but price is high can change the catch effort relationship independent of biomass change.
Fishery independent surveys, using established sampling protocols and standardised fishing gear are a way in which catch rates can be standardised irrespective of gear efficiencies or fisher’s behaviour. If these surveys can also produce accurate estimates of exploitation rate then accurate estimates of biomass can be achieved, provided the exploitation rate estimates are representative of the fishing grounds. Fishery independent estimates of exploitation rate are thus a valuable way of validating model biomass estimates especially with the introduction of an ITQMS where the relationship between catch rates and legal-sized biomass was likely to change pre- and post-quota.
This project aimed to trial change-in-ratio (CIR) and index-removal (IR) techniques to obtain estimates of exploitation rate and biomass from broad scale regions in the fishery.
Keywords: southern rock lobster, change-in-ratio, index-removal, exploitation rates, tagging.
Indicators for density and biomass of exploitable abalone – developing and applying a new approach
Evaluation of egg production as a method of estimating spawning biomass of redbait off the east coast of Tasmania
Redbait are an important component of the pelagic ecosystem, being a major consumer of zooplankton and a prey species for predators such as tunas, birds and mammals. The introduction of large-scale mid-water trawl operations (2001) to target small pelagics in Zone A of the Small Pelagic Fishery has produced catches of redbait that have no precedent locally and there is real potential for further rapid expansion. Little information is available on the biology or population dynamics of redbait, and there are no assessments of stock size on which to base TACs, currently set at 34,000t (combined species, including management triggers).
The development of a method for estimating redbait biomass is urgently required to support the setting of scientifically defensible TACs. Fishery-dependent methods of assessing fish stocks are generally unsuitable for small pelagic species due to their schooling behaviour and targeted nature of the fishing operations. Furthermore, due to the very recent development of mid-water trawling targeting redbait, no time series of data are available to detect changes in redbait stocks off Tasmania. The daily egg production method (DEPM) has been applied successfully for biomass estimation of a variety of small pelagic species, and is deemed suitable for estimating redbait biomass. There are advantages in generating biomass estimates as early as possible in the development of this fishery, if fishery impacts are to be detected and managed.
FRDC has supported the evaluation of DEPM for blue mackerel (Project 2002/061), a species that co-occurs with redbait. There are considerable efficiencies in establishing linkages with this project in terms of research focus, expertise and resources. However, as redbait have a different spawning season to blue mackerel, the timing of blue mackerel egg surveys are not appropriate and therefore additional research is required to evaluate the feasibility of using DEPM for redbait.
Final report
Estimating the biomass of fish stocks using novel and efficient genetic techniques
Development of software for use in multi-frequency acoustic biomass assessments and ecological studies
Final report
The development of the ECHO software has enabled the collection and analysis of large multifrequency acoustic data sets. The data can now be processed in a timely manner (via overlays) to quality assure and interpret underlying acoustic characteristics in the signals. From these analyses we can perform seabed and biomass processing on the individual frequencies. Alternatively the three frequencies can be mixed in a visual display that highlight distinct species groupings.
In the deep water orange roughy fishery the multi-frequency analysis clearly identified the dominant species groupings that occur. These combined echograms show that the community composition around the spawning aggregation is complex and not truly represented in commercial trawling operations. This will have a significant impact on the interpretation of acoustic biomass estimates. The ability to remotely sense the acoustical dominant species composition using multi-frequencies is a major advance in fisheries acoustic research.
The ECHO software has enabled us to develop methods to remotely sense fisheries habitat as well as ensuring high data quality. The software developed in this study was used to process acoustic seabed data obtained from the FRDC South East Fishery research project, Bax and Williams (1998) using simple classification methods. This project and associated software development was used to provide data to the acoustic benthic habitat FRDC project 93/058, Pitcher et al (1998). This enabled the development of enhanced bottom classification methods. We have further developed the processing techniques in this report and demonstrated that the use of multiple frequencies can improve seabed misclassification rates from 27% at a single frequency to 8% at multiple frequencies. This could lead to a major advance in our ability to correctly classify different fisheries habitats and to monitor the long term stability of these habitats.