Updated purse seine bycatch estimates in the WCPO

The Western and Central Pacific Fisheries Commission (WCPFC) has a responsibility to assess the impact of fishing on non-target species. In this report, we estimate the bycatch of the large-scale purse seine fishery operating primarily in tropical waters of the WCPFC Convention Area east of 140°E. These large vessels, typically greater than 500 tonnes carrying capacity, have been responsible for approximately 85% of the purse seine catch of tropical tunas in recent years, a catch that has varied between 1.7 and 2.2 million tonnes annually since 2010.

This report provides an update to the equivalent report prepared in 2018 and submitted to WCPFC SC14. We summarise bycatches for 45 species and/or species groups that provide comprehensive coverage of finfish, billfish, shark and ray, sea turtle and marine mammals observed in purse seine catches. We do not report on seabird bycatch due to the low number of observed catch events. Available observer coverage for 2020 represented 29% coverage of total sets, compared with annual coverage rates ranging from 62 - 78% for the period 2010-2019. This is partially due to incomplete loading of 2020 observer trips at the time of preparing the report, as well as difficulties in placing observers caused by the Covid-19 pandemic. As such, the bycatch estimates of 2020 should be considered preliminary.

The report concludes with recommendations to the Scientific Committee:
• The Scientific Committee note the estimates of bycatch of the large-scale equatorial purse seine fishery in the WCPFC Convention Area;
• The Scientific Committee note that the bycatch estimates should be interpreted as the bycatch that would have been recorded by observers with 100% coverage of fishing events;
• The Scientific Committee note that other studies suggest that shark bycatch estimates are likely to be underestimates, due to underestimation of captures by observers;
• The Scientific Committee consider whether the estimated effects from the fitted presence/absence models, in combination with time-series of bycatch rates, have utility in identifying species of potential concern that may warrant more detailed investigation;
• The Scientific Committee consider whether the estimates of purse seine bycatch should be made publicly available in electronic format to facilitate extraction and use of data by Commission Members, Cooperating Non-members and participating Territories (CCMs), and potentially other stakeholders.