Habitat selection by two beluga whale populations in the Chukchi and Beaufort seas
Date Published: February 24, 2017
Publisher: Public Library of Science
Author(s): Donna D. W. Hauser, Kristin L. Laidre, Harry L. Stern, Sue E. Moore, Robert S. Suydam, Pierre R. Richard, Christopher A. Lepczyk.
There has been extensive sea ice loss in the Chukchi and Beaufort seas where two beluga whale (Delphinapterus leucas) populations occur between July-November. Our goal was to develop population-specific beluga habitat selection models that quantify relative use of sea ice and bathymetric features related to oceanographic processes, which can provide context to the importance of changing sea ice conditions. We established habitat selection models that incorporated daily sea ice measures (sea ice concentration, proximity to ice edge and dense ice) and bathymetric features (slope, depth, proximity to the continental slope, Barrow Canyon, and shore) to establish quantitative estimates of habitat use for the Eastern Chukchi Sea (‘Chukchi’) and Eastern Beaufort Sea (‘Beaufort’) populations. We applied ‘used v. available’ resource selection functions to locations of 65 whales tagged from 1993–2012, revealing large variations in seasonal habitat selection that were distinct between sex and population groups. Chukchi whales of both sexes were predicted to use areas in close proximity to Barrow Canyon (typically <200 km) as well as the continental slope in summer, although deeper water and denser ice were stronger predictors for males than females. Habitat selection differed more between sexes for Beaufort belugas. Beaufort males selected higher ice concentrations (≥40%) than females (0–40%) in July-August. Proximity to shore (<200 km) strongly predicted summer habitat of Beaufort females, while distance to the ice edge was important for male habitat selection, especially during westward migration in September. Overall, our results indicate that sea ice variables were rarely the primary drivers of beluga summer-fall habitat selection. While diminished sea ice may indirectly affect belugas through changes in the ecosystem, associations with bathymetric features that affect prey availability seemed key to habitat selection during summer and fall. These results provide a benchmark by which to assess future changes in beluga habitat use of the Pacific Arctic.
Arctic marine ecosystems are influenced by many factors but particularly the annual formation and retreat of sea ice, which typically reach seasonal extremes in March and September. Sea ice is a key physical factor affecting the life history and distribution of marine mammals in the Arctic [1,2]. Polar bears (Ursus maritimus) and ice-associated pinnipeds such as seals and walruses use sea ice as a platform for foraging, reproduction, and resting (e.g. [3,4]). Seasonal sea ice cycles also indirectly affect access and localized productivity for Arctic marine mammals, which is the primary pathway that sea ice affects the foraging behavior and movements of Arctic cetaceans [5,6].
We acquired 2047 daily locations from Chukchi belugas and 1776 from Beaufort belugas during July–November. Model selection identified a single best model for each month-sex-population combination, except in October for Chukchi males and in November for Beaufort males, when multi-model inference was applied to two top models with <2 ΔAICc (Table 4). We selected the top model in a few cases where alternatives were within <2 ΔAICc, but were essentially the same models other than a squared ice term or an interaction factor between ice concentration and bathymetry (e.g. models 5 and 7, Table 3). Monthly models were highly predictive of habitat selection, except for Beaufort females in September–November and Beaufort males in October–November when sample sizes of tagged whales were smallest (Table 5). Beluga whales, like many migratory marine predators, are confronted by dynamic environmental conditions that influence habitat use over a range of spatial and temporal scales (e.g. [12,45,46]). Habitat selection in Arctic environments can thus indicate important features affecting the distribution of beluga populations, but may also reflect influences of social or sexual resource partitioning [22,47,48]. We developed highly predictive monthly models that revealed large variations in seasonal habitat selection between sex and populations within a remote marine region experiencing rapid environmental change.
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