Research Document - 2013/017

Results of Foxe Basin walrus (Odobenus rosmarus rosmarus) surveys: 2010-2011

By R.E.A Stewart, J.W. Hamilton, and J.B. Dunn

Abstract

Through periods of August and September of 2010 and 2011 a project was undertaken to enumerate walrus in Foxe Basin, a portion of the Central Arctic walrus population. Satellite-linked radio transmitters were deployed in 2010 (11) and 2011 (23) prior to concurrent boat and aerial surveys. Based on previous observation and close consultation with the Hall Beach Hunters and Trappers Association and the Igloolik Hunters and Trappers Organization, surveys were designed to capture the maximum number of walrus on land. The surveys attempted to include all known and suspected walrus haulout sites in Foxe Basin, along with most of the coastline and islands. Survey crews captured digital imagery of walrus on land and in the water. These were used for counting and generation of a Minimum Counted Population (MCP). Weather and logistics caused the surveys to span several days, during which walrus could move from one haulout to another. To reduce the probability of consequent double-counting, a time-distance criterion was applied, which resulted in final counts being based on fewer haulout sites than were examined. The MCP of haulout counts only (MCP_HO) was adjusted to account for walrus not hauled out at the time of the surveys using an estimate of the maximum proportion hauled out concurrently (0.74) derived from other studies (MCP_HO/0.74). We also used data from satellite tags in operation in Foxe Basin at the time of the surveys to adjust the MCP_HO for walrus not hauled out during the surveys (MCP_HO/% tags dry). In 2010, the MCP was 3,861; MCP_HO/0.74 was 5,200 (Coefficient of Variation (CV) = 0.07); and MCP_HO/% tags dry was 6,480 (CV = 0.383). In 2011, MCP was 6,043; MCP_HO/0.74 was 8,153 (CV = 0.07); and MCP_HO/% tags dry was 10,379 (CV = 0.42). In both years, coverage was incomplete and the number of haulouts included in the final estimates was further reduced to avoid double counting. In 2011, there may have been 13,452 (CV = 0.43) walrus present if it is assumed that the tagging data from a single haulout were representative of other haulouts. However, it is not possible to test this assumption with current information.

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