Research Document 2021/050

Abundance and total allowable landed catch estimates from the 2017 aerial survey of the Cumberland Sound beluga (Delphinapterus leucas) population

By Watt, C.A., Marcoux, M., Hammill, M.O., Montsion, L., Hornby, C., Charry, B., Dunn, J.B., Ghazal, M., Hobbs, R., Lee, D.S., Mosnier, A., and Matthews, C.J.D.

Abstract

Cumberland Sound (CS) beluga (Delphinapterus leucas) are genetically differentiated and spatially segregated from other beluga populations, remaining in CS year-round. Under the Species at Risk Act the population is listed as Threatened. A survey in 2014 estimated approximately 1,150 (CV = 0.216) belugas in this population. A new series of visual and photographic surveys were flown during July and August 2017. The visual survey covered a larger area of CS than previous surveys, based on input from the Pangnirtung Hunters and Trappers Association, and was divided into three strata. The photographic survey provided full coverage of Clearwater Fiord, where CS beluga congregate in summer. Visual surveys of each of the three CS strata were flown twice, and analysed as a 600 m strip transect survey adjusted for perception and availability bias. The availability bias adjustment factor was calculated from whales equipped with satellite tags in 2006–2008 and was based on time spent in the upper 0–5 m for the visual survey (C_a = 2.54; CV = 0.050). Perception bias was calculated using duplicate sightings from the primary and secondary observers during the 2017 survey (C_a\p = 1.05; CV = 0.077). The photographic survey of Clearwater Fiord was conducted once during the first survey and four times during the second survey (using a weighted-CV average for the abundance estimate for the second survey) and adjusted to account for availability bias by evaluating the time spent in the 0–1 m or 0–2 m bin depending on beluga visibility (C_a = 4.46; CV = 0.117 and C_a = 2.06, CV = 0.056, respectively). The fully adjusted estimate for the two surveys of the entire area was 1,749 (CV = 0.423) and 1,379 (CV = 0.043) whales in Clearwater Fiord. This resulted in an average 2017 survey abundance estimate of 1,381 (CV = 0.043; 95% CI = 1,270–1,502) belugas, respectively. A model incorporating the 2017 and four previous survey estimates (1990–2014), along with harvest statistics from 1960–2017, was then fit using Bayesian inference to provide updated estimates of abundance and potential impacts of different harvest scenarios. The population model produced an estimated median abundance of 1,090 (CV = 0.207, 95% CI = 617–1,864) beluga in 2018. The model estimated 96% probability of stock decline in 10 years with the current annual quota (41) and a 0%, 25%, and 50% probability of population decline with harvests of 0, 14, and 20 beluga, respectively. PBR was calculated using reproductive rates of 0.04 (assumed for cetaceans) and 0.03 (estimated from the model) and varied from one to three animals, with a TALC of one to two whales.

Research Document 2021/050 (PDF, 896 KB)

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