Abstract
In summer, narwhals (Monodon monoceros) migrate from Baffin Bay to northeastern Canada and northwest Greenland, where they are hunted by Inuit for subsistence. To prevent localized depletion, management of narwhals is based on summer stocks. The High Arctic Cetacean Survey (HACS), conducted in August 2013, was the first survey to estimate abundance of all 4 Canadian Baffin Bay narwhal summer stocks, as well as putative stocks in Jones Sound and Smith Sound, in the same summer. Narwhal abundance was estimated using a double-platform aerial survey. Distance sampling methods were used to estimate detection probability away from the track line. Mark-recapture methods were used to correct for the proportion of narwhals missed by visual observers on the track line (i.e., perception bias). We used a data-driven approach to identify single and duplicate sightings, using 4 covariates to compare differences in sightings made by front and rear observers based on: time of sighting, declination angle, group size, and species identity. Abundance in fjords was estimated using density surface modelling to account for their complex shape and uneven coverage. Estimates were corrected for availability bias (narwhals that are not available for detection because they are submerged when the aircraft passes overhead) using a new analysis of August dive behaviour data from narwhals equipped with satellite-linked time depth recorders. Corrected abundance estimates were 12,694 (95% CI: 6,324–25,481) for the Jones Sound stock; 16,360 (95% CI: 3,833–69,836) for the Smith Sound stock; 49,768 (95% CI: 32,945–75,182) for the Somerset Island stock; 35,043 (95% CI: 14,188–86,553) for the Admiralty Inlet stock; 10,489 (95% CI: 6,342–17,347) for the Eclipse Sound stock; and 17,555 (95% CI: 8,473–36,373) for the East Baffin Island stock. Total abundance for these 6 stocks was estimated at 141,908 (95% CI: 102,464–196,536). Sources of uncertainty arise from the high level of clustering observed, in particular in Admiralty Inlet, Eclipse Sound, and East Baffin Island, as well as the difficulty in identifying duplicate sightings between observers when large aggregations were encountered.
Highlights
A large meta-population of narwhals (Monodon monoceros) overwinters in Baffin Bay and Davis Strait (Heide-Jørgensen, Hansen, Westdal, Reeves, & Mosbech, 2013)
This analysis provides updated, corrected abundance estimates for 6 narwhal summer stocks, which together comprise most of the narwhals found in Baffin Bay
It is the first time these stocks have been surveyed in the same summer, and the first time that abundance estimates are available for the putative Jones Sound and Smith Sound summer stocks
Summary
A large meta-population of narwhals (Monodon monoceros) overwinters in Baffin Bay and Davis Strait (Heide-Jørgensen, Hansen, Westdal, Reeves, & Mosbech, 2013). In late spring, these narwhals migrate to the fjords and inlets of northeastern Canada and northwest Greenland, where they spend the summer before migrating back to their wintering grounds in Davis Strait and Baffin Bay in late fall. Inuit from across Nunavut hunt narwhals for subsistence on the whales’ summering grounds or along their spring and fall migration routes, in the Qikiqtani and Kitikmeot regions, which include the Boothia Peninsula, Baffin Island, and the Canadian High Arctic communities (Priest & Usher, 2004). Narwhals appear relatively sedentary in summer, with telemetry studies indicating that tracked animals tend to remain in the aggregation areas where they were tagged and rarely visit other summering areas
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