Habitat Preference of Risso's Dolphins (Grampus griseus) off the South Coast of Portugal

Abstract

Information on the occurrence and ecology of Risso's dolphins off the southern coast of Portugal is limited and poorly understood. This study investigated the occurrence of this species in the Algarve via presence-absence models. In total 63 Risso's dolphin sightings were recorded with an average group size of 10 animals and a presence of immature animals in most groups (73.02%). Generalized Additive Models were fitted to test how static and dynamic oceanographic variables affected Risso's dolphin occurrence between 2010 and 2020, from a presence-absence dataset. The optimal model showed that Risso's dolphins' probability of occurrence was higher close to the coast, and positively related to sea surface temperature, reaching a maximum presence probability between 22°C and 24°C. A positive but nonsignificant relationship between chlorophyll-a concentration with 1 month time lag and Risso's dolphin presence was also detected. This study provides a first step to understanding habitat preference of Risso's dolphins in the south of Portugal and identifies this area's importance for the species.