Abundance estimates for Beluga ‪(Delphinapterus leucas)‬ in James Bay and the Belcher Islands-Eastern Hudson Bay area in Summer 2024

Abstract

Systematic line-transect surveys were flown in James Bay and the Belcher Islands-eastern Hudson Bay area from July 18th to September 23rd, 2024. A total of 620 groups of beluga (1,154 individuals) were detected by primary observers, of which 547 had perpendicular distance measurements. A single gamma detection function was selected to model the probability of detection in both surveyed areas from the ungrouped distribution of perpendicular distances, which estimated an average effective strip half-width of 756 m (CV = 8.7%). A total of 481 groups with an average size of 1.91 (CV = 6%) animals were detected in James Bay over 4,033 km of survey lines, resulting in a surface abundance index of 4,349 (95% CI: 2,761–6,851) beluga. The Belcher Islands-eastern Hudson Bay area was split into a high coverage stratum, and two low-coverage strata located to the north and in Tasiujaq Lake (formerly Richmond Gulf). The plan was to survey the high coverage stratum twice to provide a more precise estimate of abundance, but unforeseen circumstances prevented the first survey of this stratum from being completed. On the second and complete survey of the high coverage area, 105 groups of beluga with an average size of 1.62 (CV = 10%) were detected over 8,327 km of transects. This yielded a surface abundance index of 479 (95% CI: 300–767) beluga. No beluga were observed in the northern low-coverage and Tasiujaq Lake strata. To ensure consistency in methodology with the 2024 survey, data from the eight surveys conducted in James Bay and the Belcher Islands-eastern Hudson Bay between 1985 and 2021 were reanalyzed by fitting gamma detection functions to perpendicular distance distributions. All surface abundance indices were corrected for availability and perception biases. For the 2024 survey, availability bias was estimated at 0.514 (CV = 3.6%). Applying a perception bias correction factor of 1.355 (CV = 7.9%) to the James Bay surface index resulted in a fully corrected abundance estimate of 11,455 (95% CI: 7,322–17,921). For Belcher Islands-eastern Hudson Bay, applying a perception bias correction factor of 1.600 (CV = 6.9%) to the surface index resulted in a corrected abundance of 1,491 (95% CI: 928–2,396) beluga in 2024. This BEL-EHB beluga abundance estimate is the lowest of the time series of nine surveys flown since 1985.