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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.
