Research Document - 2016/014

Estimating abundance and total allowable removals for walrus in Foxe Basin

By M.O. Hammill, P. Blanchfield, J.W. Higdon, D.B. Stewart, S.H Ferguson

Abstract

Walruses are harvested in the Foxe Basin area for subsistence, and there is a limited sport hunt. Here we examine historic and recent walrus surveys, conducted by DFO over a time span of almost three decades, to assess whether there is any evidence of a change in walrus abundance. Aerial surveys were flown in 1983, 1988, 1989, 2010 and 2011. The 1983 surveys were counts of hauled out animals using methods similar to recent surveys flown in 2010 and 2011. The 1988 and 1989 surveys used strip transect survey methods. The 1983 survey had a haulout count of 2,314, while the strip transect surveys produced estimates of 5,128 (SE=4,390) and 5,510 (SE=1,644), respectively. Four recent counts in 2010 and 2011 were between 2,409 and 6,043. Although different methods were used, there is no evidence for a temporal trend in abundance over the last 28 years. The 2010 and 2011 surveys were re-analysed using a simple count approach only and a haulout proportion of 0.37 (SE=0.16) based on satellite transmitter deployments in Foxe Basin during the same years. The resulting abundance estimates are 10,435 (SE=4,513) in 2010 and 14,093 (SE=6,704) in 2011. The total allowable removals (TAR) were estimated from the Potential Biological Removal (PBR) calculations with an R_max of 0.07 or 0.08 and, a Recovery factor of 0.5 or 1.0. Depending on the R_max, recovery factors, and whether the 2010 or 2011 abundance estimate was used, the TAR varied from 129 to 385.

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