Research Document - 2015/058

Abundance estimate of the Eastern Canada – West Greenland bowhead whale population based on the 2013 High Arctic etacean Survey

By T. Doniol-Valcroze, J.-F. Gosselin, D. Pike, J. Lawson, N. Asselin, K. Hedges and S. Ferguson

Abstract

Bowhead whale hunting is an integral part of Inuit culture. Up-to-date abundance estimates of the entire Eastern-Canada West-Greenland (EC-WG) bowhead population are necessary to support sustainable management of the harvest. A multi-year survey design was chosen in 2002-2003 because two separate populations of eastern Arctic bowhead whales were still recognized at the time. Since then, eastern Arctic bowheads were re-assessed as a single population. No aerial surveys had attempted to cover the full extent of bowhead whale summer distribution in the Eastern Canadian Arctic in a single year.

DFO conducted the High Arctic Cetacean Survey (HACS) in August 2013 to update abundance estimates for known stocks of Baffin Bay narwhal and for the EC-WG bowhead whale population. The survey was designed to cover the largest possible proportion of the summering areas of the EC-WG population while at the same time improving on the precision of past estimates. Three aircraft were used simultaneously to cover the vast survey area within a short time frame. This document presents the results of the survey and new abundance estimates for the EC-WG bowhead population, as well as an updated Potential Biological Removal (PBR) estimate.

Distance sampling methods were used to estimate detection probability away from the track line. Mark-recapture methods were used on the sighting data from two platforms on each side of the aircraft to correct for the proportion of whales missed by visual observers. Abundance in Isabella Bay was estimated using density spatial modelling to account for its complex shape and uneven coverage. Estimates were corrected for availability bias (whales that are not available for detection because they are submerged when the plane passes overhead) using a new analysis of satellite-linked time depth recorders transmitting information on the diving behaviour of bowhead whales in the study area in August.

The survey achieved complete coverage of important summer aggregation areas like Prince Regent Inlet, Gulf of Boothia, Admiralty Inlet, Eclipse Sound, Isabella Bay and Cumberland Sound. However, Fury and Hecla Strait, Northern Foxe Basin and Roes Welcome Sound could not be covered. The fully corrected abundance estimate for the EC-WG bowhead whale population was 6,446 (Coefficient of Variation [CV] 26%). Sources of uncertainty arise mainly from the high level of clustering observed at several scales, in particular in Isabella Bay and Cumberland Sound. Based on this abundance estimate and a recovery factor of 0.5 in the PBR calculation, the EC-WG bowhead whale population can support a total human-induced mortality of 52 whales annually.

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