Updated stock status indicators for silky sharks in the eastern Pacific ocean (1994-2014)
The results of two recent genetics studies support assessing and managing the populations of silky sharks (Carcharhinus falciformis) in the western and eastern Pacific Ocean separately. One of the studies suggests a further division of silky sharks in the eastern Pacific Ocean (EPO) into two stocks, approximately along the Equator. An attempt by the IATTC staff to assess the status of the silky shark in the EPO using conventional stock assessment models has been severely handicapped by major uncertainties in the fishery data, mainly regarding catch levels in the early years, which may be why the model is unable to explain the population declines observed in the early period of the assessment (1994-1998) (Document SAC-05 INF-F). Although this stock assessment attempt has produced a substantial amount of new information about the silky shark in the EPO (e.g., absolute and relative magnitude of the catch by different fisheries and their selectivities), the absolute scale of population trends and the derived management quantities are compromised. Therefore, an alternative scientific basis for management advice is urgently needed. Since a conventional stock assessment was not possible, the staff proposed a suite of possible stock status (or stability) indicators (SSIs) which could be considered for managing the northern and southern stocks of silky sharks in the EPO (SAC-05-11a). The present paper updates the indices based on standardized catch-per-unit-effort (CPUE) in purse-seine sets on floating objects (CPUE-OBJ) with data for 2014.