Environmental preferences of sharks bycaught by the tuna purse-seine in the Eastern Pacific Ocean

Eric Díaz Delgado

Sharks play important ecological roles in marine ecosystems. However, due to their life-history traits and low resilience, their vulnerability increases with overexploitation. The Eastern Pacific Ocean (EPO) purse-seine fishery catches several pelagic sharks as bycatch. Therefore, describing the environmental preferences of bycaught sharks is crucial to improve fisheries management. This study aims to describe the environmental preferences and spatiotemporal distribution of six shark species within the EPO through Generalized Additive Models (GAMs). Results showed that almost 90% of sharks bycatch occurred on floating objects (OBJ), being the silky shark (Carchahinus falciformis) the most captured species (95.2%) between 2003-2018. Blue shark (P. glauca) was mostly bycaught in warm and productive waters around the Baja California Peninsula. Blacktip (C. limbatus) and silky sharks were mainly found in warm coastal and offshore waters of southern Mexico. Oceanic whitetip shark (C. longimanus) was restricted to warm and oceanic waters with low productivity. Meanwhile, scalloped and smooth hammerhead sharks (Sphyrna lewini & S. zygaena) were bycaught in warm and productive waters around the Baja California Peninsula and Peruvian waters. The obtained results allowed us to identify hotspots where fisheries management can be implemented, improved, or modified (e.g., temporal closures) for reducing shark bycatch.
Keywords: Generalized Additive Models; spatiotemporal distribution; set type; fisheries management; floating objects