Updated Stock Status Indicators For Silky Sharks In The Eastern Pacific Ocean, 1994-2018

The indices of relative abundance for large silky sharks (Carcharhinus falciformis) in the eastern Pacific Ocean (EPO), developed from bycatch-per-set in purse-seine sets on floating objects and presented at the 9th meeting of the Scientific Advisory Committee (SAC-09) in May 2018 (Document SAC-09-13), were updated with data from 2018. Previous analyses (SAC-08-08a(i), Lennert-Cody et al. 2019) identified a correlation between north EPO indices, particularly for small and medium silky sharks, and interannual variability in oceanographic conditions, and thus the indices for those size categories, and for all silky sharks, were not updated because of concerns about bias. In both the north and south EPO, the indices for large silky sharks for 2018 decreased to about their 2016 values, following an increase in 2017. Because of recent increases in the number of sharks recorded as released alive, indices for large silky sharks that included these data were also calculated, and showed a somewhat less pessimistic long-term trend. However, there is concern that the size category of sharks released alive may be poorly estimated, and thus the increase in live release could bias the indices by size. In addition, a recent Pacific-wide silky shark assessment (Clarke et al. 2018) highlighted the need for a better understanding of movements and stock structure of the species in the Pacific Ocean, and Project H.5.a could be expanded to include additional research on the effects of inter-annual variability in oceanographic conditions (e.g., El Niño and La Niña events) on silky shark distribution and movements. Considerations for future research, including some presented previously (SAC-07-06b(i), SAC-07-06b(iii), SAC-08-11) on improving shark fishery data collection in the EPO, are also presented.