Distribution and abundance of beluga whales in the Mackenzie estuary, southeast Beaufort Sea, and west Amundsen Gulf during late July 1992

Abstract

Three Twin Otter aircraft, each with three or four observers, were used to conduct a systematic survey of the southeast Beaufort Sea (4.5-6.3% coverage), Mackenzie estuary (15-29% coverage), and west Amundsen Gulf (2.9% coverage) over a 55-h period on 23-25 July 1992. Beluga whales (Delphinapterus leucas) were found throughout the estuary and offshore strata, with the highest density in Kugmallit Bay, Mackenzie estuary (1.137 beluga/km2). Over 85% of the beluga were estimated to be offshore, where they were widely distributed at low densities (0.099-0.311 beluga/km2). Data collected by primary observers (experienced in aerial surveys) yielded an estimate of 15 307 (95% CI 12 305 - 18 309) beluga visible at the surface. Six reviewers independently assessed which sightings made by secondary observers (community participants with limited aerial survey experience but with experience searching for beluga from boats) did not duplicate primary sightings. These were used to adjust the primary counts for missed-at-surface and about-to-surface beluga, and yielded an index of stock size of 19 629 (95% CI 15 134 - 24 125) visible beluga; this does not account for those far below the surface and therefore unavailable to the observers, or those outside the study area. © 1996 NRC Canada.