Abundance estimates of narwhal stocks in the Canadian High Arctic in 2013
An aerial survey was conducted for six narwhal summering aggregations (hereafter referred to as stocks) in the Canadian High Arctic in August 2013. This is the first time that a survey counted all of the Canadian High Arctic narwhal stocks during one summer, and the first time for narwhals in Jones Sound and Smith Sound. The total estimate for the Canadian High Arctic was 141,909 (Coefficient of Variation, CV by stock ranged from 20 to 65%) narwhals.
This survey combined two abundance estimation methods that were summed to produce an estimate of total abundance:
spatial modelling was used to estimate densities in narrow fiords; and
mark-recapture distance sampling was used to estimate narwhal density from line transects elsewhere.
Total abundance estimates include a correction for perception bias (caused by observers missing narwhals present at the surface) estimated from duplicated sightings between the primary (front) and secondary (rear) observers.
Abundance estimates were also corrected for availability bias (to account for the fraction of time diving whales are visible near the surface) computed from the percentage of time satellite-tagged narwhals spent within 2 meters of the surface (or 1 meter in fiords with murky waters). The correction for availability bias was 2.94 (and 4.53 in fiords of East Baffin Island).
Stock specific abundances rounded to 500 were 12,500 for Jones Sound, 16,000 for Smith Sound, 50,000 for Somerset Island, 35,000 for Admiralty Inlet, 10,500 for Eclipse Sound, and 17,500 for East Baffin Island for a total of 142,000 narwhal in the Canadian High Arctic.
Assuming fidelity of narwhals to six specific summering stocks and based on the abundances estimated in 2013, the Total allowable landed catch (TALC) advice for the six summering stocks are 76 for Jones Sound, 77 for Smith Sound, 658 for Somerset Island, 389 for Admiralty Inlet, 134 for Eclipse Sound, and 206 for East Baffin Island for a total of 1,540 narwhals per year. If narwhals from the Eclipse Sound and Admiralty Inlet areas are considered as belonging to a single unit, the TALCs cannot simply be summed. The TALC advice for a combined unit would be 542 narwhals.
Allocation of the catch to communities should be done in a way that accounts for the seasonal hunts of mixed stocks.
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