Updated purse-seine indicators for silky sharks in the EPO

The indices of relative abundance for the silky shark (Carcharhinus falciformis) in the eastern Pacific Ocean (EPO), developed from catch-per-set in purse-seine sets on floating objects, and presented at the 8th meeting of the Scientific Advisory Committee (SAC-08) in May 2017 (Document SAC-08-08a(i)), were updated with data from 2017. In both the north and south EPO, the indices for large silky sharks and for all silky sharks were similar, or increased slightly, relative to their 2016 values, while the indices for medium and small silky sharks were similar, or decreased slightly, relative to their 2016 values. Work subsequent to SAC-08 (Lennert-Cody et al. submitted) supported the previous conclusions (SAC-08- 08a(i)) that the north EPO indices, particularly the small silky shark index, are influenced by inter-annual variability in ocean-climate forcing, and are therefore potentially biased as indicators of stock status. Future work (Project H.5.a) will attempt to adapt the current catch-per-set standardization methodology to develop indices that are less influenced by such variability, with emphasis on the indices for large silky sharks. In the meantime, the IATTC staff reiterates its previous recommendations (SAC-07-06b(i), SAC- 07-06b(iii), SAC-08-11) regarding improving shark fishery data collection in the EPO. This will facilitate the development of other stock status indicators and/or conventional stock assessments to better inform the management of the silky shark and other co-occurring shark species. Spatio-temporal models that combine data from multiple gear types to improve spatial coverage should also be explored in the future, to facilitate modeling efforts once data from other sources become available.