Science Advisory Report 2013/034

Estimates of Abundance and Total Allowable Removals for Atlantic Walrus (Odobenus rosmarus rosmarus) in the Canadian Arctic

Summary

• Results of recent aerial surveys and satellite telemetry studies were used to develop abundance estimates for six walrus stocks that make up the high Arctic and central Arctic populations in Canada.
• Individual stock abundance estimates are likely negatively biased, due to incomplete survey coverage, inter-annual variability in walrus distribution, weather and ice conditions.
• The quality and amount of satellite tag data, used to adjust surveys for animals missed by the survey, varied among surveys and, at least in Foxe Basin, may not have been representative of the whole population. More satellite data are required to develop better adjustment factors for the haulout counts.
• Based upon the derived abundance estimates, a range of total allowable removals (TARs) was calculated for each stock using the Potential Biological Removal method (PBR). For each stock, these estimates were compared to reported harvests in Canada between 1985 and 2010.
• The Baffin Bay (BB) stock was estimated at approximately 1,250 walrus in 2009, based on a count of 571, resulting in a TAR of 10-11.
• The west Jones Sound (WJS) stock was estimated at 503 (coefficient of variation (CV) = 0.07) walrus in 2008, based on a count of 404, resulting in a TAR of seven or eight.
• The Penny Strait-Lancaster Sound (PS-LS) stock was estimated at between 661 (CV = 2.08) and 727 (CV = 0.07) walrus in 2009, based on a count of 557, resulting in a TAR of 10-12.
• Partitioning harvest to the three stocks comprising the high Arctic population was not possible, but the 25-year average reported harvests in Canada (approximately 14) are less than the combined TAR sum (27-31).
• Estimated size for the combined north and central Foxe Basin stocks (N&C-FB) in 2011 ranged from 8,153 (CV = 0.07) to 13,452 (CV = 0.43) walrus, based on counts of 6,043 and 4,484, respectively, using different dates and different adjustment factors. The calculated TARs of 106-166 straddle the lower 95% confidence limit of recent harvest levels (approximately 185), which do not include other human-caused mortality. Better survey coverage and better information on current removals are required, as is further investigation into walrus movements within Foxe Basin and exchange with the larger Hudson Bay-Davis Strait stock.
• Only a small portion of the Hudson Bay-Davis Strait (HB-DS) stock range has been surveyed. Numbers of walrus summering in the Hoare Bay area on southeast Baffin Island in 2007 were estimated at between 1,420 (CV = 0.07) and 2,533 (CV = 0.17), based on a count of 1,056. The calculated TARs are 18-38 and the local harvest is approximately 36.
• The central Arctic population as a whole lacks sufficient data for a meaningful population estimate and subsequent advice on TARs.
• Uncertainty exists for all areas: survey counts are negatively biased; most surveys suffer from incomplete coverage; most adjustment factors are based on small samples or data from other places and times; harvest statistics are incomplete and losses unreported.
• The BB stock and the West Greenland-southeast Baffin Island component of the HB-DS stock are shared with Greenland. Further investigations into movement patterns between Canada and Greenland and total hunting mortality from both countries are required.
• The estimates of TARs presented cannot be partitioned among various sources of human-caused mortality. For all stocks, additional information is required about harvest levels, hunting losses, and other types of human-caused mortalities such as net entanglement and ship strikes before providing sustainable harvest advice.

This Science Advisory Report is from the October 29 to November 2, 2012 annual meeting of the National Marine Mammal Peer Review Committee (NMMPRC). Additional publications from this process will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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