Determination of the stock structure of three tropical tuna species across the western Pacific Ocean at scales of relevance to the ETBF: A scoping study

[摘要] The ETBF exploits stocks of tropical tunas (yellowfin, bigeye and albacore tunas) that are shared across a range of fisheries in the adjacent Pacific Ocean and are managed under the Western and Central Pacific Fisheries Commission (WCPFC). Current assessments assume that these species comprise single discrete stock units throughout the WCPFC region. Although considered to comprise either one stock or two within each hemisphere under current regional management regimes, the degree of connectivity across the regions at which the three species are assessed is still a major source of uncertainty.Domestic harvest strategies for Commonwealth fisheries, including the ETBF, have been developed and implemented by the Australian Fishery Management Authority (AFMA) under the Commonwealth Harvest Strategy Policy and Guidelines. The harvest strategy developed for the ETBF aims to provide a means by which assessments of each of the five principal species (albacore, bigeye and yellowfin tunas, broadbill swordfish and striped marlin) can be produced and a Recommended Biological Commercial Catch (RBCC) determined. Following the development of the harvest strategy framework, comprehensive evaluation in order to produce fully specified harvest strategies using a detailed management strategy evaluation (MSE) framework was undertaken. Across all five species, the harvest strategy framework demonstrated sensitivity to population connectivity, the effects of the non ETBF fleet (the wider western and central Pacific Ocean fleet) on the overall population and a lack of agreement between catch per unit effort time series for domestic fleets with that used in broader stock assessments. A number of unresolved issues and associated recommendations were highlighted as a result of the evaluation of the harvest strategy framework including resolution of stock structure and the spatial connectivity of species populations between the ETBF and the broader western and central Pacific Ocean. These initial findings have been supported by more recent investigations into the effectiveness of the harvest strategy on the five main target species.In response to current uncertainty in the understanding of the connectivity of tropical tunas in the ETBF with the broader western Pacific Ocean, this project aimed to assess:1. Information on the connectivity and stock structure of, in particular, the three tropical tunas within the western and central Pacific Ocean;2. Knowledge gaps relating to the connectivity of each species in the western and central Pacific Ocean;3. Research and monitoring required addressing these priority knowledge gaps, and in relation, a workplan for specified research.Information available from which insights into the spatial connectivity of tropical tunas could be derived included commercial catch data, biological information on growth rates and reproduction, movement data derived from tagging studies, hard part chemical signatures and the results of genetic investigations. Spatial and temporal variability can be found to varying degrees across datasets for all species, however interpretation of many datasets is currently limited either by sampling design, numbers of samples, variability in methods used or the ability of methods to resolve potential structure in samples. What variability that is present however suggests that there is likely to be some structure to stocks throughout the WCPFC region and assumptions of single spawning populations may not be accurate.Genetic methods have undergone a technical revolution in the last decade and in association, can now achieve much higher resolution than was possible in the past. Genomic approaches now offer solutions to a number of problems in fisheries management, allowing identification of individual fish at the level of (i) species, (ii) population, and (iii) individual. In addition, these methods are now much more cost effective than they have previously been. The advantage is that ...

[发布机构] CSIRO

[效力级别] Marine and Estuarine Ecology (incl. Marine Ichthyology) [学科分类] 地球科学(综合)