Indices of abundance based on standardised CPUE are critical inputs to both the stock assessments of tunas and billfish and associated harvest strategies. However, a major constraint for assessing multi-species fisheries is a lack of reliable abundance indices that are a pre-requisite for the accompanying stock assessments. Improvements in our ability to standardise multi-species CPUE will therefore improve the accuracy of assessment outcomes as well as implementation of harvest strategies such as those used in multi-species fisheries such as the Eastern Tuna and Billfish Fishery (ETBF) which are rely heavily on standardised CPUE. Within the ETBF standardised CPUE indices for some target species display large inter-annual variation which is not thought to truly reflect variation in the stock availability. The multi-species nature of the ETBF also means that it can be difficult to standardise CPUE for individual species as changes in the targeting of different species can change CPUE in a manner not related to stock abundance. Imperfect CPUE standardisation impacts on the output of the harvest strategy, in particular the Recommended Biological Commercial Catches (RBCC). New techniques to improve the CPUE standardisation would consequently improve the quality of resultant RBCCs and subsequent TACCs. There will also be follow-on improvements in assessing the status of other pelagic resources (e.g. byproduct and bycatch speices, both domestically and internationally), most of which rely on the standardisation of CPUE. The recent CPUE Standardisation Workshop held by TTRAG in March 2013 supported this need which was also subsequently endorsed by TTMAC which included the project “Identification, application and appraisal of novel statistical techniques for use in the CPUE standardisation“ as a high priority in the annual research statement for 2013/14.
Final report
This project was undertaken by a collaboration of senior fishery scientists at CSIRO and from New Zealand, together with a former fisheries manager now with the Commonwealth Department of Agriculture and Water Resources in Canberra, on the development of methods to construct indices of stock abundance trends from commercial catch-per-unit-effort (CPUE) in multispecies pelagic longline fisheries. Such indices are crucial inputs into stock assessments undertaken around the world and play a vital role in achieving the sustainable management of global fisheries. The project work was undertaken during 2015 and 2016, using the multispecies longline fishery for tuna and billfish on the east coast of Australia (the Eastern Tuna and Billfish Fishery) as the example case study. As indices of stock abundance constructed from CPUE data are the central inputs into the harvest strategy used in this fishery to inform the determination of annual Total Allowable Commercial Catch (TACC) limits, there was a need to identify the accuracy of current methods and develop new methods to construct more reliable indices of stock abundance. In this regard, the analyses undertaken during the project and presented here were designed to address specific issues related to this fishery.
However, it is also hoped that the general results of this project will have broader applicability to other multispecies species, both domestically and internationally.
