Summary of population structure of IOTC species from PSTBS-IO project and recommended priorities for future work

Davies C, Marsac F, Murua H, et al (2021) Summary of population structure of IOTC species from PSTBS-IO project and recommended priorities for future work. In: WCPFC Scientific Committee 17th Regular Session. WCPFC-SC17-2021/SA-IP-13, Electronic Meeting

Also published as IOTC-2020-SC23-11_Rev1.

In 2017, CSIRO in collaboration with AZTI Tecnalia (Spain), IRD (France) and CFR (Indonesia) commenced a 3-year collaborative project on population structure of tuna, billfish and sharks of the Indian Ocean funded by the European Union and the consortium partners (PSTBS-IO). The project aimed to describe the population structure and connectivity of priority tuna and tuna-like species within the Indian Ocean, as well as blue and scalloped hammerhead sharks. Genetic analysis of new and archived tissue samples was the primary method, complimented by microchemical analysis of otoliths. The project also aimed to extend collaborative research networks among partners and contribute to technical capacity building in participating coastal states. Sampling was completed between late 2017 and early 2019 with a total of 5,767 tissue samples and 3,010 otoliths collected or made available to the project from partner archives. Of these, 3,610 tissue samples have been genotyped and 689 processed and analysed for otolith microchemistry. The final data coverage for each species across their range within the Indian Ocean varied among the study species and between genetics and microchemistry methods. For genetics, good sample coverage was achieved for the six neritic and tropical tuna species and swordfish; while the coverage for albacore, the two other billfish species and blue shark limited the power of analyses to examine population structure within the Indian Ocean. The restrictions associated with CITES listing of scalloped hammerhead precluded useful coverage of this species in the project. The sample coverage for otolith microchemistry was often less complete for each species than for genetics due to the logistic difficulty in obtaining otoliths, relative to tissue samples, particularly in the case of larger, more valuable adults. Good coverage was achieved for kawakawa and Spanish mackerel and the three tropical tunas, whereas the lack of otolith samples from the south-east Indian Ocean for albacore limited the scope of inferences that could be made based on microchemistry for this species. The project has provided a sound foundation for exploring specific hypotheses on population structure related to stock assessment and management purposes for the majority of the study species and a good foundation for extending the coverage for the remainder. The preliminary results for each species and method were presented to the 2019 meeting of the Scientific Committee and the final, detailed results from the current project have been presented and reviewed by the respective IOTC Working Parties through 2020. Here, we provide a high-level summary of the population structure results (and links to the detailed working papers) and recommendations on necessary next steps to build on the foundations established and momentum generated by this project. These include, that the IOTC support: i) the review, discussion and consultation with scientists on the results of the project, their limitations and utility for stock assessment and management purposes, with a view to identifying priorities to be considered by the SC and Commission; ii) convening a workshop of relevant experts to provide advice on the use of results for the short and medium term, relative to the priorities identified in i); and iii) development of a targeted biological sample collection program, including tissue and otolith collection for future population structure studies, based on i) and ii), that consolidates and extends the networks developed through this and other recent and current initiatives.