| Summary: | Thesis (Ph.D.)--University of Washington, 2021 The Chukchi Sea is experiencing rapid environmental change due to warming temperatures, reductions in sea ice, and increases in transport of warm southern-origin waters into the region. Continued changes in the physical environment may further alter the marine ecosystem, resulting in changes in the community structure and composition. This dissertation examines the role of the environment in structuring the distribution and composition of the pelagic fish community in the eastern Chukchi Sea. Using a multi-platform approach centered around the use of fisheries acoustics, I investigate the impact of changing climate on the distribution of age-0 gadids that have historically dominated the pelagic fish community in the Chukchi Sea in summer. Chapter 2 uses repeat acoustic surveys conducted using autonomous surface vehicles and particle tracking simulations to examine potential movement of the age-0 gadid population in summer. During summer, the size of fishes increased during a period of wind-driven retention on the shelf, indicating that the Chukchi shelf may serve as an important nursery region for these age-0 fishes. Chapter 3 investigates the changes in the abundance and distribution of pelagic fishes observed in summer acoustic-trawl surveys in 2012, 2013, 2017, and 2019. While age-0 Arctic cod (Boreogadus saida) remain the dominant pelagic fish, walleye pollock (Gadus chalcogrammus), a boreal species, have become increasingly abundant in recent years, driven by increases in temperature and transport on the Chukchi Sea shelf. This suggests that environmental conditions now allow pollock to extend their northern range into the southern and central Chukchi Sea, at least on a seasonal basis. In Chapter 4, two years of seafloor-mounted moored echosounder observations are used to identify the seasonal abundance and movement of the age-0 fishes observed in summer. The moorings identify strong seasonal trends in fish abundance and pelagic community composition driven ...
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