Occurrence and distribution of cetaceans in the waters around the Azores (Portugal), Summer and Autumn 1999–2000

Abstract

Boat-based surveys were conducted during the summer and autumn months of 1999 and 2000 around the islands of the Archipelago of the Azores to determine occurrence, distribution, and relative abundance of cetaceans. A total of 222 cetacean schools, corresponding to 11 species, were sighted over the two years. Cetaceans were widely distributed in the area surveyed, but the central group of islands recorded the highest relative abundance of cetaceans and the greater species diversity. Within each group of islands, cetaceans were more abundant in the coastal area (to 9 km from shore) than in the oVshore area (9 to 28 km). Atlantic spotted dolphins (Stenella frontalis ), short-beaked common dolphins ( Delphinus delphis ), and bottlenose dolphins (Tursiops truncatus ) were the most frequently sighted species and were found in all the islands surveyed. Although there was considerable overlap in spatial distribution among these species, common dolphins and bottlenose dolphins occurred in coastal areas, while Atlantic spotted dolphins were more common in o Vshore and deeper waters.