| Summary: | Thesis (Ph.D.)--University of Washington, 2022 The Northern Indian Ocean (NIO) is a region of high environment variability driven by seasonally reversing winds. The southwest monsoons generate substantial plankton blooms in these tropical waters and shape biogeography of higher trophic levels. Cetaceans in oceanic waters are good indicators of epipelagic and mesopelagic prey bases. This dissertation examines species composition and distribution of cetaceans in a mid-oceanic island habitat in southeastern Arabian Sea. I use passive acoustic monitoring (PAM), which is particularly useful to collect data year-round including night periods and the rough-weather southwest monsoon season when visual surveys are challenging. In Chapter 2, I examine the occurrence and species composition of the cetacean community in the Lakshadweep archipelago via visual surveys using a platform of opportunity. The surveys documented 139 sightings, including eight odontocete species and one mysticete species. Occurrence of cetacean species differed across seafloor slope gradients and distances to nearest landmass. In Chapter 3, I investigate baleen whale occurrence in Lakshadweep waters using PAM. The study showed occurrence of Central Indian Ocean (CIO; formerly Northern Indian Ocean) acoustic population of blue whales in Indian waters. These results extend the known range of CIO pygmy blue whales about 1000 km north-westward from the waters surrounding Sri Lanka. In Chapter 4, I determined the occurrence and temporal patterns of island-associated odontocetes in Lakshadweep waters using PAM. A resident population, likely to be spinner dolphins, was identified. Whistle occurrence was significantly influenced by month, site, and diel and lunar cycles. Similarities of odontocete occurrence to other mid-oceanic island chains suggest that an island-associated micronekton community may exist around Lakshadweep. In Chapter 5, I characterize dominant sound sources to the shallow water reef soundscape in Lakshadweep and their correlation with ...
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