Year-Round Dive Characteristics of Male Beluga Whales From the Eastern Beaufort Sea Population Indicate Seasonal Shifts in Foraging Strategies

Abstract

Dive behavior represents multiple ecological functions for marine mammals, but our understanding of dive characteristics is typically limited by the resolution or longevity of tagging studies. Knowledge on the time-depth structures of dives can provide insight into the behaviors represented by vertical movements; furthering our understanding of the ecological importance of habitats occupied, seasonal shifts in activity, and the energetic consequences of targeting prey at a given depth. Given our incomplete understanding of Eastern Beaufort Sea (EBS) beluga whale behavior over an annual cycle, we aimed to characterize dives made by belugas, with a focus on analyzing shifts in foraging strategies. Objectives were to (i) characterize and classify the range of beluga-specific dive types over an annual cycle, (ii) propose dive functions based on optimal foraging theory, physiology, and association with environmental variables, and (iii) identify whether belugas undergo seasonal shifts in the frequency of dives associated with variable foraging strategies. Satellite-linked time-depth-recorders (TDRs) were attached to 13 male belugas from the EBS population in 2018 and 2019, and depth data were collected in time series at a 75 s sampling interval. Tags collected data for between 13 and 357 days, including three tags which collected data across all months. A total of 90,211 dives were identified and characterized by twelve time and depth metrics and classified into eight dive types using a Gaussian mixed modeling and hierarchical clustering analysis approach. Dive structures identify various seasonal behaviors and indicate year-round foraging. Shallower and more frequent diving during winter in the Bering Sea indicate foraging may be energetically cheaper, but less rewarding than deeper diving during summer in the Beaufort Sea and Arctic Archipelago, which frequently exceeded the aerobic dive limit previously calculated for this population. Structure, frequency and association with environmental variables supports the use of other dives in recovery, transiting, and navigating through sea ice. The current study provides the first comprehensive description of the year-round dive structures of any beluga population, providing baseline information to allow improved characterization and to monitor how this population may respond to environmental change and increasing anthropogenic stressors.

Environmental drivers of beluga whale distribution in a changing climate: a case study of summering aggregations in the Mackenzie Estuary and Tarium Niryutait Marine Protected Area

“…However, as the habitat model was built only on turbidity and temperature, the area 9 presented conditions deemed unfavourable for belugas and modelled as such. Additionally, while EBS belugas have been observed feeding in the estuary (Ostertag et al 2019), recent findings seem to point to the offshore as favoured foraging areas (Hornby et al 2017;Storrie et al 2022). Finally, it was unclear why some areas were of high relative probability of selection (2, 6, and 7 in Fig.…”

Investigating the dynamics of methylmercury bioaccumulation in the Beaufort Sea shelf food web: a modeling perspective

“…The model simulates the beluga MeHg concentration assuming that they exclusively forage in the BSS yearround. However, Beaufort beluga whales only spend summer in the eastern Beaufort Sea and Mackenzie Delta region, and they migrate through the Chukchi Sea to the Bering Sea where they spend winter, 39,95,96 with the feeding contribution of the Beaufort Sea unknown. The consistency between simulated and observed MeHg concentrations in major dietary items of beluga (e.g., Arctic cod, cisco & whitesh) suggests that belugas' dietary exposure of MeHg in the Beaufort Sea is not overestimated.…”

“…The observed MeHg concentration of beluga came from subsistence harvests in the Mackenzie Delta, 39 where about 90% of the landed catch of Beaufort beluga in the past occurred in July, shortly aer their spring migration from Bering Sea. 96,100 Given belugas' foraging behavior in the Chukchi and Bering Seas prior to summering in the BSS and the long half-life time of MeHg in other mammals (51 days in ringed seals, 68 50-80 days in human populations 101,102 ), the MeHg uptake in the Chukchi and Bering seas should account for a signicant fraction of the MeHg burden in these beluga whales, even aer they forage in Beaufort for 1-2 months prior to the harvest. We estimate that only 16 to 44% of MeHg in Beaufort beluga whales comes from their food uptake in the Beaufort Sea (Fig.…”

Group characteristics and spatial organization of the Eastern Beaufort Sea beluga whale (Delphinapterus leucas) population using aerial photographs

“…The aerial survey was designed based on the last population abundance assessment in 1992, recent beluga tagging projects in the Canadian Beaufort Sea, and consultation with Inuvialuit representatives Storrie et al 2022). Different survey protocols were applied between offshore and inshore areas based on the primary objective of assessing population abundance (e.g., Watt et al 2021).…”

“…The Eastern Beaufort Sea (EBS) beluga whale population is one of the largest beluga populations in Canada, estimated at approximately 32 500 whales Muto et al 2021). Each year, EBS belugas migrate to the Beaufort Sea, following the retreat of sea ice in the spring (Asselin et al 2011;Hornby et al 2014) and spend the summer travelling between the Mackenzie Estuary, Amundsen Gulf, and M'Clure Strait (Richard et al 2001;Storrie et al 2022). From early to late July, EBS belugas show high fidelity to the Mackenzie Estuary (Brown Gladden et al 1997;Harwood et al 2014), where large aggregations of nearly 2000 whales have been recorded .…”