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10692
Open
Diversity and relative abundance of cetaceans in coastal waters off Liberia, based on a geophysical survey
Koen Van Waerebeek and Howard Gray
The presence of cetaceans off northwestern Liberia was studied for the first time during a 3D seismic survey from 21 January to 4 May 2009. We documented 126 sightings of cetaceans, ten of which were mixed species assemblages, and confirmed ten species (eight odontocetes and two mysticetes), eight of which were new range state records for Liberia. Habitat covered included the outer continental shelf, slope and offshore trenches (depths ranging 100-3,000 m). Five species, or genera, were frequently encountered (>5 sightings), including (declining order) Globicephala macrorhynchus, Stenella attenuata, Tursiops truncatus, Balaenoptera spp. and Physeter macrocephalus. Two rorquals were identified as Balaenoptera brydei, while seven others remained unidentified. Occasionally encountered species (≤ 4 sightings) included Stenella longirostris, Steno bredanensis, Grampus griseus, Delphinus sp. and Megaptera novaeangliae. A humpback whale at this southern latitude in late March, and in deep water, raises a question about stock identity. Of nine sightings of T. truncatus, four were mixed sightings with pilot whales, pointing to an offshore ecotype. Two small groups of sperm whales were mixed with 100 and 50 unidentified dolphins. The absence of sightings of Peponocephala electra and Lagenodelphis hosei, common species in Ghanaian waters, is notable.