Movements and Inferred Foraging by Bowhead Whales in the Canadian Beaufort Sea during August and September, 2006–12

Abstract

Each spring, most bowhead whales of the Bering-Chukchi-Beaufort (BCB) population migrate to the southeast Beaufort Sea and summer in Canadian waters. In August and September, they form aggregations, which are known to occur mainly in the shallow, shelf waters when oceanographic conditions promote concentration of their zooplankton prey. The movements of individual bowheads while they occupy these late summer habitats are less well known; our knowledge is based on photographic evidence and limited tagging studies conducted from 1982 to 2000. In this study, 85% (17) of the 20 satellite-tagged whales that could have spent some time in the Canadian portion of the Beaufort Sea during late summer 2006 to 2012 spent all or part of August and September there. We analyzed location data for 16 whales, using a two-state switching correlated random walk (CRW) behavioural model, and classified locations in the Canadian waters as associated with lingering behaviour (inferred foraging) or directed travel. We found that these whales spent the greatest proportion of their time lingering (59%), followed by traveling (22%), and transitioning between lingering and traveling (19%). Using only lingering locations for these tagged whales in all study years pooled, we calculated kernel densities and defined five areas within the 75% density contour as aggregation areas. Together, the five aggregation areas we defined comprised 25 341 km2, 14.1% of the total area used by these tagged whales in Canadian waters during August and September of the deployment years. Three aggregation areas were located in shallow waters of the Beaufort Sea Shelf and were used almost exclusively by immature tagged whales in our sample. Two other aggregation areas were observed, one in Darnley Bay and one in Viscount Melville Sound in the Canadian Arctic Archipelago. Each of these was used by one mature whale. Tagged whales were observed to use one or two aggregation areas in a single season, and rarely more. The proportion of lingering time spent in each aggregation area was highly variable among individuals. The largest aggregation area (10 877 km2), located over the Beaufort Shelf north of the Tuktoyaktuk Peninsula (5 – 52 m depth), was used by 13 of the 16 tagged whales, almost exclusively by the immature whales, including three of four that were tracked in two consecutive summers. The Beaufort Shelf overall (and possibly the Tuktoyaktuk Shelf, including the Outer Shelf, in particular) was especially important for immature bowhead whales, while mature whales used habitats beyond the Beaufort Shelf during late summer. Findings may be important to inform both decisions on management and mitigative actions relating to bowhead whale use of the Beaufort Shelf and studies that aim to improve our understanding of the prey base of BCB bowhead whales in the Canadian Beaufort Sea region.

Seasonal patterns in acoustic detections of marine mammals near Sachs Harbour, Northwest Territories

“…This trend of arriving in the Canadian Beaufort Sea in late April and departing in October is consistent with telemetry studies of this population (Mate et al 2000;Citta et al 2015;Harwood et al 2017) and long-term monitoring in Alaska (Braham et al 1980). Citta et al (2015) specifically demonstrated that bowhead whales use the polynya at Cape Bathurst early in the season, which stretches from the Tuktoyaktuk Peninsula to Cape Bathurst and north towards Banks Island, and later in the season, bowhead whales mostly use the shallow shelf adjacent to the Tuktoyaktuk Peninsula.…”

“…These authors still identified the area around Sachs Harbour as a 95% core use area, but it was not as well used as the Cape Bathurst polynya or the Tuktoyaktuk Peninsula. Harwood et al (2017) found similar core use areas for juvenile bowhead whales, but also found that juvenile bowhead whales spent quite a bit of time moving around Banks Island and identified a few core use areas farther north. One acoustic study (Clark et al 2015) recorded in August and September 2009 and 2010 near Tuktoyaktuk found the presence of bowhead whale calls nearly every day, which confirms that bowhead whales stay in the Canadian Beaufort Sea into September.…”

“…The shipping season in the western Canadian Arctic also occurs late in the summer and during the autumn migration of bowhead and beluga whales. The shipping corridor through the area tends to follow the coastline ) and overlaps with the migration route of both whale species (Citta et al 2015;Harwood et al 2017;Hauser et al 2017a). Ships traveling the current corridor pose risks for these marine mammals, including risks of ship strikes and acoustic impacts (Reeves et al 2014;Halliday et al 2017).…”

“…Both bowhead and beluga whales time their migration into the Beaufort Sea based on ice breakup (Clark et al 2015;Hornby et al 2016), typically migrating into the region in early spring. The western Canadian Arctic is an understudied area in the range of all four marine mammal species, particularly for studies documenting distribution and seasonal patterns, with a few sporadic studies using aerial surveys for bowhead (e.g., Harwood et al 2010) and beluga whales (e.g., Harwood et al 1996) and satellite telemetry studies for bowhead (e.g., Citta et al 2015;Harwood et al 2017) and beluga whales (e.g., Richard et al 2001;Hauser et al 2014). The distribution of both seal species has been studied periodically for the last 40 years (e.g., Stirling et al 1977), although more effort has focused on ringed seals (e.g., Harwood and Stirling 1992).…”

Mercury and stable isotope cycles in baleen plates are consistent with year-round feeding in two bowhead whale (Balaena mysticetus) populations

“…The BCB population overwinters in the Chukchi and the northern Bering Seas and spends the summer in the Alaskan and Canadian Beaufort Sea (Moore and Reeves 1993;Schell and Saupe 1993;Moore et al 2010;Harwood et al 2017). The EC-WG population overwinters in Hudson Strait, northern Hudson Bay, east of Baffin Island, and near the ice edge along West Greenland (Koski et al 2006;HeideJørgensen et al 2007;Ferguson et al 2010).…”