Distribution and Abundance of the Eastern Canada – West Greenland Bowhead Whale Population Based on the 2013 High Arctic Cetacean Survey

Abstract

The hunting of bowhead whales (Balaena mysticetus) is an integral part of Inuit culture. An up-to-date abundance estimate of the entire Eastern Canada – West Greenland (EC-WG) bowhead population is necessary to support sustainable management of this harvest. The High Arctic Cetacean Survey (HACS) was conducted in August 2013, primarily to update abundance estimates for known stocks of Baffin Bay narwhal (Monodon monoceros). As the ranges of narwhal and bowhead largely overlap, the survey area was expanded to cover the summer range of bowhead whales. Bowhead whale abundance was estimated using 3 aircraft to cover the large survey area within a short time frame. Distance sampling methods were used to estimate detection probability away from the track line. Double platform with mark-recapture methods were used to correct for the proportion of whales missed by visual observers on the track line (perception bias). Abundance in Isabella Bay, an area known for high bowhead density, was estimated using density surface modelling to account for its complex shape and uneven coverage. Estimates were corrected for availability bias (whales that were not available for detection because they were submerged when the aircraft passed overhead) using a recent analysis of satellite-linked time depth recorders transmitting information on the diving behaviour of bowhead whales in the study area in August of the same survey year. The fully corrected abundance estimate for the EC-WG bowhead whale population was 6,446 (95% CI: 3,838–10,827). Possible sources of uncertainty include incomplete coverage and the diving behaviour of bowhead whales. These results confirm earlier indications that the EC-WG stock is continuing to recover from past overexploitation.

Developing a Precautionary Management Approach for the Eastern Canada-West Greenland Population of Bowhead Whales (Balaena mysticetus)

“…One explanation for this discrepancy may be the delayed population growth from the continued commercial whaling in the early 1900s when few whales were available. Another explanation for this mismatch is that the three aerial survey abundance estimates used in our trend analysis were all negatively biased due to missing areas known to have bowhead whales (Koski et al, 2006;Dueck et al, 2008;Doniol-Valcroze et al, 2020). Another explanation was the uncommonly long delay in sexual maturity of females, longer than any other whale species (Ferguson and Higdon, 2013), resulted in a delay in exponential population growth.…”

“…For most species it is extremely difficult to estimate reference points based on population trend; even more so for large whales like bowhead (Witting, 2013). The most recent ECWG aerial survey was conducted in 2013 and produced an abundance estimate of 6,745 (95% CI 3,722-11,200) whales (Doniol-Valcroze et al, 2020). This estimate is conservative, because it does not include the summer aggregation areas of Foxe Basin and Repulse Bay.…”

“…Models included a uniform distribution for struck and lost correction that ranged from 1.10 to 1.20, and a uniform distribution for R max that ranged from 0.035 to 0.045. Recent population estimates are shown for comparison, from aerial surveys (circle symbols) in 1981 (Koski et al, 2006), 2002(IWC, 2009b(Doniol-Valcroze et al, 2020 and from genetic Capture-Mark-Recapture analysis (2013), blue triangle symbol (Frasier et al, 2020)]. Upper panel (A) is model results that include zero values and lower panel (B) is model results that exclude zero population abundance values.…”

“…The second aerial survey occurred in August 2002 and resulted in a number of estimates due to different analyses but the best estimate considered here was conducted by the IWC (2009b) of 6,344 (95% CI = 3,119-12,906) whales. The most recent aerial survey, conducted in 2013, used distancesampling and double platform with mark-recapture methods and estimates were corrected for availability bias using analysis of satellite-linked time depth recorders produced a fully corrected abundance estimate of 6,446 (95% CI: 3,838-10,827) (Doniol-Valcroze et al, 2020). However, all aerial surveys are considered to provide conservative estimates because they do not include all of the known range of the population.…”

“…The ECWG bowhead whale population has increased considerably since its near extirpation (Doniol-Valcroze et al, 2020;Rekdal et al, 2015), and now requires a harvest management framework that provides subsistence value to Inuit communities. Using the 2013 aerial survey estimate of 6,446 whales (Doniol-Valcroze et al, 2020) and a recovery factor of 0.5 in the PBR formulation, calculates that the ECWG bowhead whale population can support a total human-induced mortality of 52 whales annually from direct losses (harvest) and indirect losses (whales struck and lost, fishing gear entanglements, and vessel strikes) (DFO, 2015).…”