Trends in strandings of marine mammals on the Galician coast during the 1990s

Abstract

Marine mammal strandings on the Galician coast (NW Spain) have been recorded continuously since 1990 by a network of volunteers (CEMMA). The database created includes six different types of records: live or dead stranded cetaceans; dead cetaceans floating offshore; confIrmed by-catches; live animals in the water that needed assistance; findings of cetacean bones and records of stranded or live pinnipeds.· Data recorded for each animal included: species, condition, measurements and weight of the whole animal. When possible, necropsies were carried out to collect teeth, stomachs, gonads and other tissue samples and to determine cause of death. A total of 1,245 strandings of at least fIfteen species of marine mammals were recorded in Galicia from 1990 to 1998. The most commonly recorded species (48% of stranded animals) was the common dolphin Delphinus delphis. Strandings of bottlenose dolphin Tursiops truncatus and harbour porpoise Phocoena phocoena were also common, representing the 11% and 7%, respectively. The number of strandings recorded per year increased from 1990 to 1998. Almost 80% of the strandings were located on the western coast of Galicia. During 1990-1998, 29 cetaceans were recorded as by-caught and signs of by-catch were seen in a further 173 cetaceans. Analysis of the seasonal pattern of strandings indicated that more strandings occurred in autumn and winter and that, in common dolphins, the average size of animals and the proportion of males both increased towards the end of the year. Sea conditions, seasonal movements of the cetaceans, the physical characteristics of the coast and proximity to fIshing and feeding grounds may influence the seasonal and geographical distribution of strandings along the Galician coast