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Cetacean Assessment & Ecology Program

Spatio-Temporal Movement Patterns of Two Alaskan Beluga Whale Stocks Based on Acoustic Detections (pg 1, 2 3)

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refer to caption

Figure 1. Belugas whales in the Arctic. Photo by Laura Morse (NMFS research permit 782-1719).

Passive acoustic monitoring using bottom-mounted recorders is a reliable and cost-effective method for monitoring the presence of some marine mammals year-round in the extreme environmental conditions present in the Arctic (extensive darkness, cold, and winter ice coverage; e.g., Delarue et al. 2011, Moore et al. 2012, MacIntyre et al. 2013). Beluga whales (Delphinapterus leucas; Fig. 1) are commonly referred to as the canaries of the sea due to their highly vocal nature. They produce a wide variety of vocalizations that can be classified as whistles, pulsed calls, noisy calls, combined calls, and echolocation clicks (Sjare and Smith 1986). These vocalizations range in frequency from approximately 200 Hz to 20 kHz, with echolocation clicks extending upwards of 120 kHz. Thus, belugas are an ideal candidate species for passive acoustic monitoring over their vast migratory range.

Within the Alaskan region (Fig. 2), five stocks or populations of belugas are recognized based on their defined summering locations or year-round residence (Allen and Angliss 2013). These are the migratory stocks of the eastern Beaufort Sea, the eastern Chukchi Sea, and the eastern Bering Sea (Norton Sound), which have distinct summering and wintering grounds, and the resident populations of Bristol Bay and Cook Inlet, which are not migratory. Genetic data suggest each population is demographically distinct (O’Corry-Crowe et al. 1997).

The aim of this study was to identify peaks in beluga vocal activity from four passive acoustic moorings, located in the northern Bering, northeastern Chukchi, and western Beaufort Seas, over a single year to understand the migratory movements and fine-scale timing of the eastern Beaufort Sea and eastern Chukchi Sea stocks as they undertake their extended migrations in the Alaskan Arctic and Subarctic. The large, eastern Beaufort Sea (EBS) stock (~40,000 individuals;Allen and Angliss 2013) migrates through the eastern Chukchi Sea, utilizing pathways such as the open-water lead that develops near the coast between Point Hope and Point Barrow (Moore et al. 2000) to summer in the Mackenzie Delta and Amundsen Gulf in the Canadian Beaufort Sea region (Harwood et al. 1996). In summer, satellite-monitored individuals from this stock moved hundreds of kilometers to the north and west, including into dense areas of pack ice (Richard et al. 2001, Hauser et al. 2014). In autumn, these individuals migrated west through the Beaufort Sea and then south through the Chukchi Sea (particularly on the western side) before crossing the Bering Strait and entering the Bering Sea at the end of November (Richard et al. 2001, Hauser et al. 2014). The smaller, eastern Chukchi Sea (ECS) stock (~3,700 individuals; Allen and Angliss 2013) spends early summer (June) along the coast of the eastern Chukchi Sea, particularly near Kasegaluk Lagoon and Kotzebue Sound (Frost and Lowry 1990). Anecdotal evidence suggests the ECS stock spends winter and spring in the northern Bering Sea, north of St. Lawrence Island (D. Hauser, pers. comm.). In summer and autumn, satellite-monitored individuals from this stock  moved from the eastern Chukchi Sea into the Arctic basin and western Beaufort Sea, where some individuals roamed widely (Suydam et al. 2001, 2005; Hauser et al. 2014). Therefore, there is seasonal overlap between the ECS and EBS stocks. (Hauser et al. 2014). In this study, we investigated the spatio-temporal movement patterns of two Alaskan beluga stocks, using long-term passive acoustic recorders to capture temporal peaks in vocal activity, to improve our understanding of the fine-scale migratory timing of these stocks for management and conservation purposes. (continued)

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