Rebuilding beluga stocks in West Greenland

Abstract

Decisions about sustainable exploitation levels of marine resources are often based on inadequate data, but are nevertheless required for practical purposes. We describe one exception where abundance estimates spanning 30 years and catch data spanning more than 40 years were used in a Bayesian assessment model of belugas Delphinapterus leucas off West Greenland. The model was updated with data from a visual aerial survey on the wintering ground in 2012. Methods that take account of stochastic animal availability by using independent estimates of forward and perpendicular sighting distances were used to estimate beluga abundance. A model that appears to be robust to the presence of a few large groups yielded an estimate of 7456 belugas (cv = 0.44), similar to a conventional distance-sampling estimate. A mark-recapture distance analysis that corrects for perception and availability bias estimated the abundance to be 9072 whales (cv = 0.32). Increasing distance of beluga sightings from shore was correlated with decreasing sea ice cover, suggesting that belugas expand their distribution offshore (i.e. westward in this context) with the reduction of coastal sea ice. A model with high (0.98) adult survival estimated a decline from 18 600 (90%

Sexual differences in the foraging ecology of 19th century beluga whales (Delphinapterus leucas) from the Canadian High Arctic

“…The δ 13 C and δ 15 N values of the late 19th century belugas from Elwin Bay were not found to differ significantly from belugas collected in the 1990s from West Greenland (Disko Bay and NOW areas; Skovrind et al, ) after accounting for the Suess Effect (MANOVA, F [2,50] = 1.10, p = .34; Wilk's Λ = 0.96, partial η 2 = 0.04) (Figure ). These areas in West Greenland should correspond to the wintering grounds of the belugas that migrate to the area around Somerset Island in the summer (Figure ; Heide‐Jørgensen et al, ). This stability in δ 13 C and δ 15 N values suggests that the foraging ecology of these belugas has remained relatively constant between the late 19th and late 20th centuries or if there have been shifts in the prey consumed, these shifts have occurred between species with comparable isotopic compositions.…”

“…Complete beluga crania and mandibles were collected from a historic whaling site on Elwin Bay, Somerset Island, in the central Canadian Arctic Archipelago (Figure 1; Friesen, Savelle & Smith, 1998). Elwin Bay is an estuarine area heavily used by the Canadian High Arctic beluga stock in the summer months before they overwinter off the west coast of Greenland near Disko Bay or in the North Water Polynya in Baffin Bay (Heide-Jørgensen et al, 2017). The belugas analyzed in this study were harvested at Elwin Bay between 1874 and 1898 (Reeves & Mitchell, 1987).…”

“…Map showing the location of Elwin Bay and the summering (shaded area around Somerset Island) and wintering areas (shaded areas around the North Water Polynya [NOW] and Disko Bay) of the Eastern High Arctic beluga stock (Heide‐Jørgensen et al, ).…”

Environmental, behavioral, and design-related factors affect accuracy and precision of beluga abundance estimates from aerial surveys

“…Availability bias corrections are often applied directly to total abundance as a proportion of time available to the survey platform, without consideration for the variability of time-in-view with perpendicular distance, i.e., not using Equation 1 (e.g., Hammond et al, 2013;Heide-Jørgensen et al, 2016;Marcoux et al, 2016;Pike et al, 2020). Our results further indicate that such an approach is likely to bias abundance estimates by an unknown and variable amount: a uniform but underestimated mean time-in-view would bias availability downward and abundance estimates upwards, whereas the reverse would lead to an underestimation of abundance.…”

“…However, surveys for marine mammals and cetaceans in particular, are logistically challenging and generally highly onerous. As a result, they are often multi-specific, with the number of replicate surveys being generally limited to one or two per year/season (e.g., Heide-Jørgensen et al, 2016;Doniol-Valcroze et al, 2020;Pike et al, 2020). Overall however, our analysis of an exceptional dataset of 8 to 14 replicate surveys per year conducted over a short period of time suggests that abundance estimates from single surveys, which is the rule for most cetacean surveys (e.g., Hammond et al, 2013;Taylor et al, 2017;Mannocci et al, 2018;Doniol-Valcroze et al, 2020;Pike et al, 2020), can be biased and imprecise.…”