UC San Diego

Interpreting the ecological role of top marine predators requires understanding lifelong foraging and distribution patterns; however, predation events are rarely observed and reliable collection of samples over the life of a fully-aquatic mammal is difficult. Stable isotope analysis (SIA) of archived tissues offers the opportunity to retroactively study long-term foraging ecology of elusive animals, particularly with biologically inert teeth or bone. My dissertation provides a framework for analyzing and interpreting decades of foraging patterns for a ubiquitous top marine predator, the killer whale (Orcinus orca), with the aims of using the past to inform future ecosystem studies and conservation strategies. In Chapter 1, I identify the appropriate experimental conditions to isolate collagen from powdered killer whale bone in preparation for SIA. I also demonstrate that the historical age of the specimen and the characteristics of the bone will not bias stable isotope values. In Chapter 2, I formally analyze assumptions in existing literature regarding sampling protocols and the effects of common treatments on SIA of dentin from teeth. In Chapter 3, I conduct a literature review to establish a library of stable isotope values for consumers in the North Pacific, which provides a foundation for my forthcoming chapters. I also generated new stable isotope values to represent the variation found within a species from age, sex, geographic location, and other parameters. In Chapter 4, I address a long-standing ecological hypothesis regarding the role of transient killer whales (Orcinus orca rectipinnus) in a historic ecosystem collapse throughout the North Pacific. In Chapter 5, I explore the historical differences in foraging ecology between two groups of resident killer whales (Orcinus orca ater) to investigate this potential driver of disparate population trajectories. My study aids in understanding the extent of dietary plasticity in resident killer whales, a key component to protecting these ‘Endangered’ and ‘Threatened’ populations.

My dissertation research contributes to our understanding of the ecology and ecosystem impacts of a top predator, as well as the broader field of utilizing archived teeth and bones of marine mammals for SIA.