Stabilisation of the abundance of bowhead whales (Balaena mysticetus) in West Greenland

Abstract

A proportion of the East Canada‐West Greenland population of bowhead whales (Balaena mysticetus) spends January–June off West Greenland. Several aerial surveys conducted between 1998 and 2012 have estimated the abundance of bowhead whales on this winter feeding ground. Following identical methods, a visual aerial line‐transect survey was conducted as a double‐observer experiment with independent observation platforms covering the main distribution of the winter aggregation of bowhead whales in West Greenland between 26 March and 4 April 2022. The target region covered an area of 34,742 km2 with six strata and a total of 3,667 km systematically placed transect lines. Abundance of bowhead whales was estimated using a Mark‐Recapture Distance Sampling (MRDS) approach. The at‐surface estimate was 208 (cv = 0.38, 95% CI: 99–436) whales. Availability correction incorporated data on diving behaviour, time‐in‐view, and the degree of diving synchrony. The mean time that whales were available for detection at the surface (23%, cv = 0.06), the mean duration of dives below 2 m (472 seconds), and the mean duration of surfacings (138 seconds), were estimated using high‐resolution time‐depth‐recorders from 12 bowhead whales instrumented in the same area and season as the survey. Drone footage showed that small groups of bowhead whales (1–3) had highly synchronous surfacing patterns and long breathing periods at the surface (mean = 21 seconds). The MRDS abundance estimate, corrected for perception bias and availability bias, was 832 whales (cv = 0.39, 95% CI: 402–1,723) bowhead whales. The 2022 estimate is similar to an estimate from 2012 but lower than the estimate from 2006, suggesting that the abundance in winter in West Greenland has stabilised.