The southern Chukchi Sea is a productive, shallow continental shelf ecosystem that is undergoing rapid change due to climate warming. Annual sea ice cover has declined significantly, potentially allowing for more temperate species to move further north into the Arctic and stay for longer periods. Monitoring the presence and occupation patterns of top predators, such as baleen whales, is important for detecting shifts in species assemblages and distributions in response to climate change. This dissertation examines the acoustic occurrence of three subarctic baleen whales in the Chukchi Sea—fin whales (Balaenoptera physalus), humpback whales (Megaptera novaeangliae), and gray whales (Eschrichtius robustus)—and seeks to uncover patterns in their presence, the environmental drivers that draw them into the Arctic, and how ships affect the acoustic habitat of the region during the open-water season. In Chapter 2, I use acoustic recordings from three moored hydrophones in the Bering Strait region from 2009–2015 to identify fin whale calls during the open-water season (July–November) and investigate the potential influence of local environmental conditions on fin whale presence. The results show significant interannual variability in the acoustic presence of fin whales with the greatest detections of calls in years with contrasting environmental conditions (2012 and 2015). Colder temperatures, lower salinities, slower water velocities, and weak southward winds prevailed in 2012 while warmer temperatures, higher salinities, faster water velocities, and moderate southward winds prevailed in 2015. Most detections (96%) were recorded at the mooring site, Site A3, nearest the confluence of the nutrient-rich Anadyr and Bering Shelf water masses, ~ 35 km north of Bering Strait, indicating that productive water masses may influence the occurrence of fin whales.In Chapter 3, I expanded my efforts to include humpback and gray whales and added two years of acoustic and environment data, 2017 and 2018, to the dataset from Chapter 2. Using recordings and in situ environmental data from Site A3 collected from 2009 to 2018, I identified fin, humpback, and gray whale calls during the open-water season (May–December), and examined the timing of migration as well as investigated potential environmental drivers of whale presence. The acoustic presence of humpback and fin whales varied across the years with the highest occurrence of humpback calls in 2009, 2017, and 2018 and the highest occurrence of fin whale calls in 2015, 2017, and 2018. The years 2013 and 2015 had the highest proportion of recordings with gray whale calls. Fin whales had significantly later departure dates during the study period (~ 3 days yr-1, p = 0.02), likely on account of warmer temperatures in the Chukchi Sea in the later years of the study (2017 and 2018). Individual models for the three species identified day of the year, sea-surface temperatures, near-bottom temperatures, and the presence of a thermal front the previous month as drivers of fin, humpback, and gray whale presence.In Chapter 4, I characterized ship activity in the Bering Strait during the open-water season (July?November) for 2013?2015 and quantified the impact of ship noise on third-octave frequency bands used by baleen whales (25?1000 Hz). Peak ship activity occurred in July?September with the greatest overlap in ship noise and whale vocalizations observed in October. Ships elevated sound levels by ~ 4 dB on average for all third-octave frequency bands combined, and sound levels exceeding 100 dB re 1 μPa for the 250-Hz third-octave frequency band were recorded from two large vessels over 11 km away from the hydrophones. The results show that ship noise has the potential to impact baleen whales in the Bering Strait and serve as a baseline for measuring future impacts of ship activity in the region.Overall, the results presented within this dissertation provide a snapshot of the presence of subarctic baleen wh
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