Marine-climate interactions with the blue shark (Prionace glauca) catches in the western coast of Baja California Peninsula, Mexico

Fishery and size data by sex of 28,110 blue sharks (Prionace glauca) from 2162 longline sets documented by observers on board 204 fishery trips from the industrial fleet based in Ensenada, Mexico during 2006-2016, were used to conduct a spatial-temporal analysis of the catch-per-unit-effort (CPUE) and its relationship with climate indices along the west coast of the Baja California Peninsula. Catch length analysis by maturity groups indicated catches were composed mainly by juvenile females (58-199 cm TL) and males (60-179 cm TL). Relationships of seasonal CPUE with sea surface temperature (SST) and Chlorophyll-a (Chl) were analyzed determining aggregations were in areas characterized by oceanographic physical processes. From the exploratory analysis of annual correlations of climate indices with CPUE, the local climate SanDiAs Index explained most variation in CPUE. A generalized additive model (GAM) with 13 predictor variables was applied to gain insight on their relationship with the total CPUE by size and sex groups. The model explained 50.5% of the total blue shark CPUE and 65.5% for juvenile females. The GAM results revealed blue shark CPUE is influenced by five relevant factors: SST, NPGO, year, latitude with distance to coast and quarter interactions, and hooks set. There is a trend to increase or decrease of CPUE when compared with the delay of NEI and SanDiAs indices in more than 1 year. Local and regional climate indices can be successful tools for forecasting blue shark catches in the Northwestern Mexican Pacific.