Updated stock status indicators for silky sharks in the eastern Pacific Ocean, 1994-2019

The indices of relative abundance for large silky sharks (Carcharhinus falciformis) in the eastern Pacific Ocean (EPO), developed from bycatch-per-set data collected by on-board observers from purse-seine sets on floating objects and presented at the 10th meeting of the Scientific Advisory Committee (SAC-10) in May 2019 (Document SAC-10-17), were updated with data from 2019. Previous analyses (SAC-08-08a(i), Lennert-Cody et al. 2019) identified a correlation between north EPO indices, particularly for small (<90 cm) and medium (90-150 cm) silky sharks, and interannual variability in oceanographic conditions, and thus the indices for those size categories, and the “all silky sharks” combined category, were not updated because of concerns about bias. In both north and south EPO, the indices for large (>150 cm) silky sharks for 2019 were at, or slightly below, the 2018 values, following a more pronounced decrease in the indices from 2017 to 2018. Because of recent increases in the number of sharks recorded by observers as released alive, indices for large silky sharks that included these data were also calculated, and showed a somewhat less pessimistic long-term trend. There has been concern about the accuracy of the size category estimates recorded for sharks released alive, which could result in the increase in live releases biasing the indices by size. However, preliminary results from a recent survey of observers suggest that they are fairly confident in their ability to estimate the size category of sharks released alive from the main release locations aboard the vessel and with the primary release methods, and that the estimates for larger sharks are less likely to be affected by where on the vessel and how the animals were released than those for smaller sharks. Nonetheless, there remains uncertainty about how the number of sharks released alive has changed since 1994, the first year for which the index is evaluated. 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.