Spatial and temporal distribution of mobulid ray species in the eastern Pacific Ocean ascertained from observer data from the tropical tuna purse-seine fishery

Abstract

This research focuses on the description of the spatial and temporal distributions of mobulid ray species (Mobula birostris, Mobula mobular, Mobula thurstoni, Mobula tarapacana and Mobula munkiana) using data from the observer program (1993-2014) of the Inter-American Tropical Tuna Commission (IATTC). The tuna purse seine operations in the region extend from 70 to 150 degrees W to 20 degrees S-30 degrees N. Significant differences on the captures per sets between fishing modes and species were found. Results showed that the most common species taken are M. thurstoni, M. mobular and M. birostris in School sets (sets on unassociated tuna schools). The temporal distributions showed high variability of the catches by species and years. The spatial distribution showed several areas of importance depending of the type of fishing, such as the coast of Peru, Galagapos or the Costa Rica Dome, and possible relationships with some oceanographic processes of the eastern Pacific Ocean (i.e. coastal and seasonal upwelling systems). The frequency of the captures per set showed that, although the greatest numbers caught in a set were very low (around 53.7\% of sets with one capture), in some areas and periods there were captures of aggregates of hundreds of individuals of some of these species, such as Galapagos Islands during December, Costa Rica Dome during August, or Baja California during June. These events are of biological interest, and may offer good opportunities for conservation. This project has been developed with the aim of identifying the most important areas for these bycatch species and thus, improving the knowledge on them to reduce their mortality.