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Passive acoustic monitoring of Arctic cetaceans: Site-specific detection probability, species identification and discrimination, and underwater soundscape with increasing shipping


Arctic marine mammal habitats are changing rapidly while marine shipping is increasing in some areas of the Arctic. Passive acoustic monitoring can increase understanding of Arctic marine mammal responses to change and to stressors, like ship traffic. The strength of inference from underwater sound recordings is limited by several factors that I address in this dissertation with the aim of improving the usefulness of acoustic monitoring findings for Arctic marine resource management. I provide spatial context for acoustic detections of bowhead whale sounds, enabling direct comparisons of acoustic presence across different locations and environmental conditions. Ice cover and noise substantially reduce the predicted listening area around underwater sound recorders. Spatially normalized acoustic detections reveal that bowhead whales utilize an area at least 140 km north of Alaska during their spring migration, migrating through large areas of >90% sea ice cover. I describe acoustic characteristics of beluga and narwhal echolocation clicks, which differ substantially in frequency content and rhythmic patterns. Sound absorption by seawater and apparent changes in animal orientation strongly affect frequency spectra of recorded clicks. Finally, I measure the underwater soundscape within a narwhal summer habitat and quantify underwater noise added by commercial ship traffic. The natural soundscape, excluding periods with nearby ships, is relatively quiet in an acoustically sheltered fiord. Distant sounds from regional shipping are apparent at a less-sheltered location open to long-range sound propagation. When ships pass the recording locations, sound levels are elevated above the median levels of natural sounds for periods ranging from 30 minutes up to >4 hours with each transit. Icebreaker and tanker ships radiate more underwater noise than general cargo and bulk carrier ships. Ship sounds overlap with common social sounds produced by narwhals and ringed seals at distances of 5 to >30 km from passing ships, possibly interfering with animal communication. Improved detection distance estimates and understanding of detection probability estimation coupled with increased confidence in detection and identification of beluga, narwhal, and bowhead sounds will facilitate passive acoustic density estimation of Arctic marine mammals, investigation of their relationships with habitat, and studies of their behavioral responses to ship traffic.

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