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.

Given AFMA’s need to satisfy its ESD objective, there is a need to consider uncertainty explicitly and identify performance indicators and harvest strategies that are as robust as possible to incorrect assumptions and misinformed interpretations of data. Use of these indicators and harvest strategies will improve the chances of achieving a reasonable balance between the conflicting objectives of long-term resource sustainability and the maximisation of economic gains.

The project also addresses to some extent two key research areas in subprogram (B) of the Wild Stock Program of the SCFA Research Committee: “Biological and socio-economic evaluation of alternative management scenarios for different species and categories of fishery to provide a framework for management planning” and “The evaluation and provision of harvest strategy models through comparison of management strategies using theory and case studies, establishing objective performance indicators for different jurisdictions and identifying options which are appropriate to the nature of the fishery”.

FRDC project 98/102 has already identified several areas where there is considerable uncertainty. However, that project has focussed on ‘generic’ data-poor species (although tailored to some extent to the actual situation for jackass morwong, pink ling, tiger flathead and spotted warehou, species that have been identified as ‘high' and 'medium' priority by SEFAG). Ideally, harvest strategy calculations should be tailored to particular species to achieve optimal outcomes. This project will evaluate harvest strategies for the four species that received initial focus in FRDC 98/102. FRDC 98/102 also focused on situations in which the fishery is based on a single gear-type only. However, it is increasingly being realised within SEFAG that even within the trawl sector there are sub-fleets, each of which differ substantially in terms of their selectivity. For example, for blue warehou, the trawl fleet off New South Wales has a selectivity pattern closer to that of the non-trawl fleet based at Lakes Entrance than that of the trawl fleet based in Portland.

One of AFMAs legislative objectives relates to providing cost-effective management. Increasingly industry is being expected to bear some of the costs associated with the monitoring on which stock assessments and hence TACs are based. There is therefore a need for an objective process for determining the trade-off between monitoring costs and the ability to which AFMAs management objectives are satisfied. The aim of this study is to examine this question within the scope of the trade-off between catch and risk.

Finally, there is a major need for stock assessment on more species in the SEF. However, although data for many species is poor, there are nevertheless fewer assessments than there could be due to a lack of software for conducting the increasingly complicated assessments demanded by stakeholders. FRDC 98/102 has developed software modules for implementing several commonly applied stock assessment methods (including “Integrated Analysis” – the basis for the current assessments for blue grenadier, school whiting, eastern gemfish, and blue warehou). If the detailed output from the software that implements these assessment methods could be available in an easily useable and visual form, this software could provide a better basis for conducting routine stock assessments.