Research Document 2020/075
Research, Monitoring and Hunter Knowledge in Support of the 2017 Assessment of the Eastern Beaufort Sea Beluga Stock
By Harwood, L,A., Zhu, X., Angasuk, L., Emaghok, L., Ferguson, S., Gruben, C., Gruben, P., Hall, P., Illasiak, J., Illasiak, J., Lennie, J., Lea, E.V., Loseto, L. L., Norton, P., Pokiak, C., Pokiak, F., Rogers, H., Snow, K., and Storr, W.
Abstract
Here we summarize harvest and biological information for the Eastern Beaufort Sea (EBS) beluga to provide an updated stock assessment that combines science and Indigenous hunter knowledge. The number of EBS beluga whales harvested annually across its range has been variable, declining significantly over the available record in Canada (1980–2015). Including estimated and known loss rates from Canada and Alaska, the average annual removal of EBS beluga 2006–2015 (includes landed and struck but lost) was 145 whales (Standard Deviation 20.7). Catches in Chukotka, Russia, are < 10 belugas per year and we estimate mortality through ice entrapment averaged < 5 belugas per year from 1966 through 2015, but that too is highly variable from year-to-year. Declining interest and dependence on traditional foods and hunting, the high cost of hunting equipment and fuel, and increasingly challenging hunting conditions due to windier weather are described by hunters as the main reasons for the decline of the harvest over time. The decline in struck but lost rates is attributed to the establishment and implementation of beluga hunting by-laws by the local Inuvialuit Hunters and Trappers Committees.
The timing of the beluga harvest did not change statistically over the 1980–2015 series, however there was consensus among hunters that whales appear to be arriving earlier to the Mackenzie Estuary in spring. Incidence and annual variation in harvests in two Amundsen Gulf communities suggest the distribution of EBS beluga in the post-Estuary period varies among years, and that in the post-Estuary period the beluga’s range during August and September may be expanding.
The Canadian harvest remains highly biased towards males, > 4 to 1 over the last 16 years. Females in the Mackenzie Delta sample averaged 36.2 growth-layer groups (GLG, corresponds to one year; SD 12.6, range 10–63, n = 246) and males averaged 29.5 GLG (SD 10.1, range 11–67, n = 901). Females in the Amundsen sample averaged 28.8 GLG (SD 17.5, range 5–62, n = 20), and males averaged 26.8 GLG (SD 11.2, range 6–61, n = 105). Using a Gompertz growth model, asymptotic lengths were 377.2 ± 1.97 cm in females (n = 287) and 435.46 ± 1.56 cm in males (n = 1,119).
Temporal trends in mean age and length were evaluated using linear regression, by gender for the Delta and for Amundsen Gulf. There were no significant changes detected in the size of females landed by Delta harvesters over the time series (n = 794, F = 0.20, p = 0.66) but there has been a significant shift to smaller males over time (n = 2,310, F = 77.21, p < 0.0001). There were also statistically significant trends over time to decreasing mean GLG age (n = 905, F = 49.04, p < 0.0001) in males and to increasing mean GLG age in females (n = 248, F = 6.25, p = 0.013). Sample size was too limited to examine for temporal trends in mean size or GLG age of belugas landed in Amundsen Gulf. Hunters provided corroborating reports of a decrease in the size of whales landed in the Delta recent years, and it was suggested by hunters that this is likely the consequence of changes in hunter selectivity in recent years. With increasingly challenging hunting conditions, opportunities for selecting the preferred large males have been noticeably reduced.
Due to the low number of females taken in the harvest, data to determine age of sexual maturity and reproductive rate for this stock are not available. Limited data available suggests that calving interval is similar to that reported for the Eastern Chukchi Sea beluga in Alaska, e.g., once every three years.
The only large-scale aerial survey of EBS beluga was flown in late July 1992, and included coverage of both the Mackenzie Estuary and the offshore Beaufort Sea and western Amundsen Gulf over three consecutive days. Extrapolated counts of surfaced beluga produced an index of stock size of 19,629 (CV = 0.229). Applying a correction factor of 2, to account for beluga below the surface, this estimate was corrected to 39,258 beluga. This estimate is negatively biased, as the survey study area did not include all of the summer range of EBS beluga, known today from telemetry.
The abundance trend cannot be assessed in the absence of a recent aerial survey. The expert observations and long-term experience of hunters participating in the assessment agreed upon a recovery factor (RF) of 0.75 for the Potential Biological Removal (PBR) calculation. The resulting PBR calculation of 487 includes all anthropogenic losses (e.g., landings, ship strikes and net entanglements), struck and lost whales, and non-reported harvests. The sum of the current Canadian and Alaskan harvests averaging 145 beluga landed and lost total, and adding 10 beluga for the purported Russian take (< 10/y), is less than a third of this PBR estimate at the present time. The stock size estimate used in this calculation is dated and needs to be updated.
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