A visual and acoustic survey for harbour porpoises off North-West Africa: further evidence of a discrete population

Abstract

The distribution of harbour porpoises Phocoena phocoena in southern Europe and along the Atlantic African coast is poorly understood, with tentative assessments suggesting a discrete West African population with a northern limit around the Straits of Gibraltar. This study describes visual and acoustic surveys for porpoises in Atlantic waters of North-West Africa in spring 2005 between latitudes of 20°N and 37°N. During this period, 276h of acoustic data were collected in all sea states (from 3 125km of trackline) and 60h (824km) of visual effort was conducted in Beaufort sea states of three or less. Harbour porpoises were seen three times on the survey trackline and on four additional occasions off the trackline. The four individuals seen in Agadir Bay (30°N) represent the northernmost living porpoises reported from the Atlantic African coasts and the first sightings of porpoises reported in Moroccan waters. In addition, 31 acoustic detections were made on the survey trackline, of which 23 were made between Dakhla (24°N) and Cap Barbas (22°N). Fishing activities off North-West Africa are intense, ranging from small-scale artisanal gillnetters to international freeze-trawlers. Further monitoring of the status of this little known and isolated population is required for effective conservation management.

Keywords: acoustics; distribution; harbour porpoise; Phocoena phocoena; West Africa

African Journal of Marine Science Vol. 29 (3) 2007: pp. 403-410