Estimation de l'abondance des bélugas (Delphinapterus leucas) dans la région de la baie d'Ungava à l'été 2022

Abstract

Systematic line-transect and coastal surveys were flown August 1-16, 2022 to determine beluga abundance and distribution in Ungava and Diana Bays in northern Quebec (Nunavik). Ungava Bay was split into a high coverage stratum in the south (lines spaced 9.3 km apart) and a low coverage stratum located in the northern portion of the bay (lines spaced 18.5 km apart). Diana and Tasiujaq Bays were also covered using the high coverage systematic line spacing. The two strata in Ungava and Tasiujaq Bay were covered twice, while the Diana Bay stratum was flown once. Four groups of beluga (6 individuals total) were detected. There were too few observations to model a detection function. Instead, these observations were combined with 341 beluga group detections from aerial surveys of eastern Hudson Bay and James Bay flown in 2021 under similar conditions and using the same aircraft and methods to fit a gamma detection function. Beaufort sea state was selected as a covariate that improved detection function model fit and provided an average effective strip half-width of 763 m (CV = 6.8%). A single group of two beluga was detected over 1,918 km of survey lines during the first pass over the southern Ungava Bay stratum, while two individual beluga were detected over 2,469 km of survey lines in the northern Ungava Bay stratum. This yielded surface abundance indices of 11 (95% CI: 2-66) and 27 (95% CI: 7-111) beluga for the southern and northern Ungava Bay strata, respectively. No beluga were detected in Tasiujaq Bay over 76 and 72 km of survey lines for the first and second passes, respectively; nor during the second pass over Ungava Bay, which represented 1,962 and 2,330 km of survey lines for the southern and northern strata, respectively. When both passes were averaged, the southern and northern Ungava surface abundance estimates were 5 (95% CI: 1-29) and 14 (95% CI: 4-48), respectively. A group of two beluga was sighted on the 63 km of survey lines in Diana Bay, resulting in a surface abundance index of 10 (95% CI: 0-536) beluga. An availability bias estimate of 0.574 (CV = 8%) and a perception bias estimate of 0.497 (CV=17%) were applied to surface indices, resulting in a corrected abundance estimate of 19 (95% CI: 4-99) for the southern Ungava Bay stratum, 49 (95% CI: 14-172) for the northern Ungava Bay stratum, and 36 (95% CI: 6-223) for the Diana Bay stratum. When combining the southern and northern Ungava Bay strata, the resulting overall abundance estimate for Ungava Bay was 68 (95% CI: 23-202) beluga. The Potential Biological Removal for beluga summering in Ungava Bay calculated based on this mean survey estimate is zero whales.