Age composition data provides the key information necessary to effectively manage fisheries. The proposal provides a mechanism where age composition data can be gained using length frequency data and age composition data from different years and sampling events, which has previously been impossible. The benefits will be a reduced need for production ageing, more timely age composition data and the ability to construct age composition data from historical length frequency data where no samples were collected for ageing.

Currently the Age-Length Key (ALK) is the most widely used numerical method for assessing the age composition in a large sample of length-frequency data. However, the application of ageing data in this approach is restricted to the original sample of length distribution (ageing data from the same year the length-frequency sample is taken). Due to this severe limitation, the ageing information must be regenerated for each new data sample. Using the Fredholm First Kind equations, previous years ageing data can be used to generate the underlying age composition from the current length-frequency data. Furthermore, the ageing data may be added to include many years, improving the robustness of the statistic which can then be used to decompose the underlying age distribution from the given length frequency.

As noted by a number of referees, the major problem with the current methods is variable recruitment. We have demonstrated that the technique is tolerant to the most extreme changes in age frequency (see accompanying text). These extreme changes in age frequency are greater than any changes that could occur naturally through recruitment. The issue of variable growth may affect the efficacy of the approach, but to our knowledge, has only been observed in two species. These are black bream and blue grenadier. It is proposed that the technique be demonstrated on blue grenadier in the first year.

The cost of collecting ageing data is high, with approximately $150,000 spent each year on ageing samples from commercially important species within the South East Fishery. Due to the cost, the number of species aged is not optimal and species are prioritised on a scientific and social-political basis. The cost-benefit of applying this approach is intuitively a large reduction in cost of ageing to industry and more timely information on the age structure of the population. A formal cost benefit analyses will need to be conducted on a species by species basis. This is a function of different cost structures for ageing different species, different numbers of samples that need to aged for each species. These different numbers of estimates that need to be made for each species is primarily due to longevity and stock structuring.

The age-structured data obtained from this project will benefit the South East Trawl Fishery, the Great Australian Bight Trawl Fishery and the Gillnet, Hook and Trap Fishery which are supported by The Integrated Scientific Monitoring Program (ISMP) and various other stock assessment programs that rely on age-structured data.

Further, age composition data will be able to be reconstructed historically from species where samples were not aged but length-frequency data were collected. This will enable age-structured population analysis where the lack of ageing data prevented these stock assessment techniques from being previously used. The net effect of this approach is to greatly improve the knowledge base from which species are managed. One of key advantages of this approach is, if successful, will at the very least compliment current methods and provide temporal and spatial coverage of age composition information which is currently cost prohibitive and only collected for a few, high value species.

The implication of a technique that can provide age-composition data free from the restriction of those associated with the ALK is more cost-effective resource management.

The proposal has been developed in two parts, the first component is a 'Proof of Concept Study' where the use of the Fredholm First Kind Equations to provide age compositions from length frequency data will be further examined. If this is not assessed as successful in a workshop environment, the project will be terminated at the end of the first year. The second and third year will examine a broad range of species.

This revised proposal focuses our original whole of ecosystem approach for blue grenadier biomass and its variability to be targeted on the development of the acoustic methodology. This refocusing has necessarily required the reduction of data collection and analysis in the environmental area. It is the considered view of the proponents (CSIRO Marine and Industry partners) that the environment variables should be explored in a more exploratory fashion within this proposal at a reduced cost. Specifically we address the refocusing and the need to explain how data collection and biomass estimation may evolve over the long term.

This project proposes to develop a cost-effective acoustic observation system that covers the primary canyon spawning locations in each of three years, and which can be implemented as an ongoing method (Kloser et al, 2001; report 99/111). In the development phase it will be necessary to carry out critical research to develop the acoustic methods to move from relative to absolute measures by understanding dominant species target strengths and identification of species. Outside the dominant canyon regions the ability to accurately identify blue grenadier is difficult due to lower density and association with other fishes of similar reflectance. Our ability to estimate biomass in this regions will be limited by species identification issues. Environment variability interpreted from acoustic recordings within and between seasons will be developed to provide ecosystem based information associated with biological, physical and oceanographic data. This research should assist to develop an understanding of the relationship between Blue Grenadier stock size their dynamics and the environmental variability leading to better management advise and MSC certification.

In the first year we plan to carry out an extensive survey using industry vessels to obtain a biomass estimate of the spawning blue grenadier. Industry vessel based acoustic surveys when planned and designed to minimise sampling error and biases should provide an index of abundance. These industry observations will be converted to an absolute assessment based on the fishes target strength, species composition and an estimate of fish turn-over on the spawning grounds. Critical research will be undertaken in this project to estimate target strength and species recognition of dominant species groups and reduce uncertainties identified in the acoustic method using information gained from a national facility research voyage in the second year. The target strength of the dominate fishes will be estimated by modelling the dominant fish species acoustic target strength as well as in-situ target strength and species composition measurements using a deep towed multi-frequency acoustic system and a targeted depth stratified biological net capture systems for identification. To model the acoustic scattering of blue grenadier it will be necessary to characterise the reflective components in the body of swimbladder, flesh, bone and lipids. This will be achieved by dissection, CAT scans and lipid extraction. Estimations of swimbladder size will be supplemented with measurements of fish buoyancy required at depth using a specialised pressure chamber. These measurements will enable a detailed scattering model to be developed and associated with in situ target strengths provide a conversion of the acoustic data to an absolute estimate of spawning biomass.

The industry and research vessel data collected at the canyon sites and on the upper slope need to be related to the larger-scale environment driving interannual variability. The high recruitment variability in this fishery is probably due to environmental factors and methods that can predict or indicate factors associated to recuitment variability are worth exploring. An earlier version of this proposal included developing low cost methods of measuring physical oceanographic, biological and biochemical metrics and comparing these to historical trends. The FRDC board and one reviewer were not supportive of this part of the proposal at this time. CSIRO Marine and Industry partners still consider that development of a balanced understanding of the biomass and the environment is worthwhile. During the project we will identify other environmental data that can be measured on an ongoing basis at low cost. In this proposal the field data collected will be related to available oceanographic information and form the basis of developing hypotheses on environmental connections. A separate proposal will follow to explore a more ecosystem based approach to the Blue Grenadier fishery management.

To advance low-cost, industry-based remote acoustic sensing methods in a strategic way requires scientific input. Once methodologies have been established and limitations identified, the stock assessment process can rely on industry acoustic data and the associated (optimized) physical and biological ground-truthing. Importantly, implementing industry-based observation systems will more formally integrate industry knowledge of fishery dynamics and variability within and between seasons into the stock assessment process. The ability to develop more integrated stakeholder based monitoring systems will provide greater ownership of the management process. In particular, the utility of industry acoustic data to provide a low-cost index of abundance for blue grenadier is an exciting prospect.

The success of this project will be determined by adoption of these results by management and industry and MSC certification. To ensure appropriate uptake of the research requires a close relationship between research providers and industry partners. To begin this relationships we have been working with the joint venture partners that hold 80% of the quota (Petuna Seafoods - Les Scott and Graham Patchel and Oceanfresh -Gerry Geen) in the industry and the associated vessels the Petuna Explorer, Ocean Dawn and Aoraki. Thus far we have trialed the acoustic monitoring method on all vessels that use the same Simrad ES60 38kHz acoustic equipment that is becoming an international standard. We successfully logged data from all the vessels during the previous winter and investigated capturing other biological and physical data with associated costs.

The industry joint venture partners have been very supportive in the pilot phase and in this proposal they will provide dedicated vessel time of two weeks in the first year as well as ongoing time for dedicated surveys in the second and third year. To ensure that the monitoring system is sustainable requires forward commitments by industry and researchers. Industry are committed to supporting the acoustic monitoring project and targeted environmental monitoring both in the short and if proved successful in the long term (see separate letter). During the project the best method of ensuring ongoing collection (at appropriate standards) and analysis of the data will be investigated under two main models. Firstly, that industry become the sole people responsible for data collection, analysis and reporting. Secondly, industry engage a suitable consultant (independent or government) to manage the continued data collection to agreed protocols and analysis of data. A necessary outcome of this research will be an appraisal of the most appropriate method to transfer the methodology. This objective will continue throughout the project and a close relationship with industry maintained through the co-principle investigator “Gerry Geen”.

The need for special research projects and individual stock assessments is detailed by the South East Fishery Assessment Group (SEFAG) and endorsed by SETMAC. The development of stock assessments for blue grenadier, and ling are high priority. Other species with high priority for quality stock assessment include blue warehou, redfish, blue-eye trevalla, and (following SETMAC 55) tiger flathead.

Blue grenadier is a species for which new data have become (or are becoming) available and for which there is a conflict between the relatively optimistic scientific advice (based primarily on an acoustic and an egg production estimate) and the more pessimistic view of several industry representatives. The stock assessment for this species will be accorded first priority. The other two species to be assessed wil be determined based on discussions with SETMAC, its research sub-committee and AFMA.