Abundance of Belugas in Cook Inlet, Alaska, 1994–2000

Beluga (Delphinapterus leucas) abundance in Cook Inlet has been estimated by several authors in the past three decades to be in the range of 300–1300 whales (reviewed in Rugh et al., 2000). In some cases, those were the sums of maximum visual counts and therefore represent minimum estimates. other cases, estimates of total abundance were made by multiplying the counts by ad hoc correction factors to account for whales that were presumed to have been missed. None of these earlier surveys were designed specifically to estimate total abundance of belugas in Cook Inlet, but they have provided useful information on distribution, behavior, ecology, and minimum abundance.

Drawing on the observations and insights from those studies, we designed a survey to estimate absolute abundance of Cook Inlet belugas. Accurate abundance estimates depend on:

1) Repeated systematic surveys for beluga groups throughout their known range, and counts of each group seen (Rugh et al., 2000). 2) Corrections for whales that were missed during the counts (Hobbs et al., 2000), in particular for: A) whales that never surfaced during the count (availability bias); and B) whales that surfaced but were missed during the count (detection bias). 3) Corrections for whales not counted because the entire group was not detected by observers during one or more surveys (calculated in this report).

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Roderick C. Hobbs, David J. Rugh, and Douglas P. Demaster. Published in Marine Fisheries Review, 62(3), 2000.