Bering-Chukchi-Beaufort Seas bowhead whale (Balaena mysticetus) abundance estimate from the 2019 aerial line-transect survey
Megan C. Ferguson
International Whaling Commission
We estimated the abundance of the Bering-Chukchi-Beaufort Seas stock of bowhead whales in 2019 to be 14,531 whales (CV = 0.540; bootstrap 95% CI [7,968, 29,376]) based on aerial line-transect surveys conducted over the whales??? summer range in the Beaufort Sea shelf and Amundsen Gulf. A geographically stratified analysis, incorporating correction factors for trackline detection probability and availability bias, was used to estimate bowhead whale abundance in three regions. The regional abundance estimate for Amundsen Gulf was 275 whales (CV = 0.550; bootstrap 95% CI [83, 654]), the eastern Beaufort Sea was 13,207 whales (CV = 0.570; bootstrap 95% CI [7,108, 27,522]), and the western Beaufort Sea was 1,049 whales (CV = 0.538; bootstrap 95% CI [252, 2,132]). A bootstrap sensitivity analysis suggested that the largest contributors to the uncertainty in the overall abundance estimate were the trackline detection probability and variability among the line-transect survey sample units. Increasing the sample size of imagery (i.e., the ???independent observer??? in the mark-recapture distance-sampling analysis used to estimate trackline detection probability) would likely reduce CV(N ??). Efficient and accurate auto-detection algorithms for large cetaceans would help streamline the photo analysis process. Furthermore, spatially explicit density modeling techniques could likely reduce CV(N ??) by accounting for the unexplained variability among samples in the geographically stratified analysis.