Show simple item record

dc.contributor.authorWild, Lauren A.
dc.date.accessioned2020-10-02T23:04:25Z
dc.date.available2020-10-02T23:04:25Z
dc.date.issued2020-05
dc.identifier.urihttp://hdl.handle.net/11122/11297
dc.descriptionThesis (Ph.D.) University of Alaska Fairbanks, 2020en_US
dc.description.abstractSperm whales (Physeter macrocephalus) remove fish from commercial fishing gear in high latitude foraging grounds. This behavior, known as depredation, occurs in the Gulf of Alaska (GOA) sablefish longline fishery and has increased in frequency and severity since the mid-1990s. Sperm whale foraging ecology and movements in the GOA are poorly understood but are important considerations to how depredation impacts fishery resources and whale behavior. The goals of this dissertation were to use stable isotope analysis to evaluate trophic connections between sperm whales and their prey, estimate the proportional contribution of various prey items to sperm whale diets, and use satellite tag data to evaluate movement and diving behavior of sperm whales in the GOA. Understanding isotopic variability in cetacean skin is important to evaluating dietary information from this tissue; thus, in chapter 1, I first analyzed the stable isotope ratios among layers of cetacean skin to determine how much variability there was within and across layers of cetacean skin. Results showed horizontal layers of cetacean skin to be significantly different isotopically, suggesting evidence of a dietary time series in layers of cetacean skin, where the innermost skin layer represents the most recent diet. These results were used in my second chapter to isolate the most recent diet of sperm whales from the inner layer of skin, and then to estimate proportional contributions of different prey to sperm whale diets. Results showed that the sperm whales sampled prefer sablefish, dogfish, skates, and rockfish, and that the proportional contribution of sablefish to sperm whale diets has increased over the past 15 years as depredation has increased in severity. Chapter three presented an analysis of twenty-nine satellite tags placed on depredating sperm whales in the GOA between 2007 and 2016 to explore movement and diving behavior and how these behaviors may be linked to prey preferences found in chapter 2. Tagged sperm whales in the GOA preferred the continental slope habitat and made long migrations along the slope toward Mexico and the Gulf of California, speeding up and switching behaviors from foraging to transiting when they left the GOA. Dive depths and durations exhibited individual variability and were significantly correlated to light levels, lunar cycles, sablefish fishery catch-per-unit-effort, and seafloor depth. Results suggest diving behavior tracks that of primary groundfish prey items, and dive depths become shallower in areas of high sablefish densities, as inferred from fishery catches, potentially reflecting depredation behavior. Together these results provide a much-improved understanding of the impact of depredation on sperm whale dietary preference, and show insights into the importance of the GOA as a foraging ground for endangered sperm whales.en_US
dc.description.sponsorshipThe North Pacific Research Board (Projects 0309, 0412, 0527, 0626, 0918, and 1217), the National Geographic Society, Oil and Gas Producers Association, NOAA Fisheries Auke Bay Lab (vessel time on F/V Northwest Explorer), NOAA's Saltonstall-Kennedy grant program (Award #NA15NMF4270271), and the Central Bering Sea Fishermen's Associationen_US
dc.description.tableofcontentsGeneral introduction -- Chapter 1: Evidence for dietary time series in layers of cetacean skin using stable carbon and nitrogen isotope ratios -- Chapter 2: Exploring variability in the diet of depredating sperm whales in the Gulf of Alaska through stable isotope analysis -- Chapter 3: Movement and diving behavior of satellite-tagged male sperm whales in the Gulf of Alaska -- General Conclusions.en_US
dc.language.isoen_USen_US
dc.subjectsperm whaleen_US
dc.subjectdieten_US
dc.subjectGulf of Alaskaen_US
dc.titleDiet and movement of depredating male sperm whales (Physeter macrocephalus) in the Gulf of Alaskaen_US
dc.typeThesisen_US
dc.type.degreephden_US
dc.identifier.departmentCollege of Fisheries & Ocean Sciencesen_US
dc.contributor.chairMueter, Franz
dc.contributor.committeeStraley, Janice
dc.contributor.committeeSigler, Michael
dc.contributor.committeeWitteveen, Briana
dc.contributor.committeeAndrews, Russ
refterms.dateFOA2020-10-02T23:04:26Z


Files in this item

Thumbnail
Name:
Wild_L_2020.pdf
Size:
9.762Mb
Format:
PDF

This item appears in the following Collection(s)

Show simple item record