Environmental preferences and size variability of Carcharhinus falciformis (Müller & Henle 1839) caught by longline fleet in the Central Mexican Pacific

The silky shark (Carcharhinus falciformis) is one of the most economically important species with high volume catches in the Central Mexican Pacific (CMP). Research on environmental preferences and species distribution helps to reduce juvenile bycatch during commercial fishing operations and benefits their conservation. The aim of this research is to analyze the size variability of C. falciformis and determine its environmental preferences. Fishing information corresponds to silky sharks sampled from 2003–2017. The catch per unit effort (CPUE) was estimated as number of organisms caught / 1000 hooks. Spatial (latitude, longitude), temporal (year, month), and biological and physical variables (sea surface temperature (SST), chlorophyll-a (Chl-a) concentration, sea surface height (SSH), study area bathymetry, and the distance to the coast) were considered to determine the silky shark environmental preferences, assessed by generalized additive models. A total of 19 672 specimens were sampled, of which 86% were juveniles. The sizes showed significant inter and intra-annual variability with lengths 48–256 cm and an average of 140 cm in total length. The best-fitted model explained 37.8% of the total deviance. The C. falciformis CPUE in the CMP was higher along the northern coastal areas during the year 2015 from May to September in SST ranging from 27–30 °C, Chl-a concentration from 0.2–0.8 mg•m−3, areas with SSH from 0.1–0.3 m, and depth greater than 3 000 m. The dominance of juvenile organisms in the CMP catches could be related to different factors, such as the impact of climatic events and intraspecific longline selectivity factor due to its characteristics as hook size, bait type, and so on. These results show the need to apply measures that allow sustainable management of this vulnerable species.