Aerial Surveys for Cetaceans in the Former Akutan, Alaska, Whaling Grounds

Аннотация

Randomized aerial surveys were flown between 26 July and 26 August 1984 to search for cetaceans in two areas of southwestern Alaska: one on both Bering Sea and Pacific Ocean sides of the Aleutian Islands near the defunct Akutan shore-whaling station, which operated from 1912 through 1938, the other overlapping continental slope and shallow continental shelf waters between the Aleutians and the Pribilof Islands. ... Searches covered about 3940 nautical miles (nm), including some 2403 nm of random transects. Sightings were made of gray whales (10 sightings, 14 individuals), fin whales (3, 11), minke whales (1, 1), unidentified beaked whales (1, 6), Dall's porpoises (47, 131), killer whales (8, 26), and harbor porpoises (4, 7). A Fourier series model was used to estimate density of Dall's porpoises as 115 individuals (CV=0.263) per 1000 sq nm on the whaling grounds and 16.6 individuals (CV=0.0) per sq nm in the Bering Sea north of the whaling grounds. These estimates are comparable to those previously reported for the same general areas (97.2 animals per 1000 sq nm, SD=49.5). There were too few sightings of other cetaceans to permit calculation of meaningful density estimates. At least four species of great whales (blue, fin, humpback and sperm) were sufficiently abundant during the first four decades of this century to support significant whaling activities within about 100 sq nm of Akutan (more than 5300 whales were caught during 23 years of whaling, 1912-39). Although previous studies of the fisheries showed a downward trend in catch per unit of effort and an increase in distance traveled to take whales, whales were still being taken at relatively high rates (0.28-0.51 whales per gross catcher day) at the end of the fishery in 1939. Populations of fin, humpback, blue and sperm whales were probably significantly reduced by shore and pelagic whaling conducted widely in the North Pacific since 1939. ...

Key words: aerial surveys, cetaceans, Bering Sea, North Pacific Ocean, historical whaling