Influence of environmental variability on the distribution and abundance of the pantropical spotted dolphin (Stenella attenuata) in the Mexican Central Pacific

Abstract

The Mexican Central Pacific (MCP) has complex oceanographic dynamics, with a well-defined seasonal pattern and influence of interannual sea surface temperature anomalies. The present study investigated the relationship between the distribution/abundance of spotted dolphins and the environmental conditions in the MCP. Dolphin sighting data were collected during January 2010–December 2015; distance to coast, sea surface temperature, and chlorophyll a (Chla) were obtained for each sighting location through georeferenced maps and satellite images. A total of 746 spotted dolphin sightings were obtained with a survey effort of 31,695 km. Spotted dolphins in the MCP showed a predominantly coastal distribution regardless of environmental conditions. Significant differences were detected concerning regional seasonal variation, with higher mean sighting rate during the stratified periods and higher density/abundance estimates during the mixed periods. Spotted dolphins showed preference for warmer conditions, with higher mean sighting rate, abundance, and distance to coast during the neutral and warm interannual periods. During the coolest conditions (cold periods), mean sighting rate and abundance decreased and spotted dolphins were located closer to the coast, where Chla concentration increased. These results suggest that changes in the distribution/abundance of these dolphins could be associated with habitat quality related to tropical (El Niño/Southern Oscillation) and extratropical (The Blob) oceanographic phenomena, which could be modulating their foraging activities.