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One of the most important species in the Eastern Pacific Ocean is the silky shark (Carcharhinus falciformis), which has been caught by artisanal fisheries, longline fleets, and as bycatch by purse-seine tuna fleet. In Central Mexican Pacific, medium-sized longline fleet based on the Port of Manzanillo, Col. captures this species throughout the year. Database recorded by the shark monitoring program of Instituto Nacional de Pesca y Acuacultura was used to analyze the spatio-temporal distribution of silky shark caught by this fleet from 2003-2017. The fishing information on catch per unit effort was also provided to determine catch /1000 hooks (CPUE). Environmental database, as sea surface temperature (SST), chlorophyll-a concentration (Chl-a), and sea surface height (SSH) was derived from satellite images. In addition, bathymetry of the study area was also considered. The effect of environmental variables on the silky shark captures was assessed by means of generalized additive models (GAMs). A total of 19 672 organisms were measured, of which 86% were juvenile individuals. Sex ratio was 0.85:1 F-M. Significant interannual variability in size was found with a decreasing trend during 2003-2006; subsequent years showed a size increase pattern every three to four years. Seasonal variability was also significant; records showed that March and August were the months when sharks with the largest length were caught. No spatial pattern was observed related to shark size and sex distribution. The study area is characterized by SST 24°-30° C, Chl-a 0.08-0.48 mg/m3 and, an SSH -0.12-0.28 m, with a significant inter- and intra-annual variability. A high correlation was observed between CPUE and SST. The best-fit model explained 27.5% of the deviance, which includes spatial variables (latitude, longitude), time (year and month), and environmental factors (SST, Chl-a, SSH, and depth). The final model suggested higher catches out of the coast from 2005-2008 and 2014-2016; from April-September in waters with sea surface temperatures from 27-28 °C, low Chl-a concentration (0.2 mg/m3), and in convergence zones with 3000 m in depth.

Palabras clave: Silky Shark; Distribution; Catches; Central Mexican Pacific

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