| Summary: | Many marine food webs are “wasp-waist” in which energy funnels through one, or few, intermediate trophic level prey species, such as forage fish. However, marine prey are patchy and ephemeral, a challenge for marine predators. Ideal Free Distribution posits that individuals will disperse “ideally” among patches, whereby patches persistently supporting more individuals can be inferred to be high quality. Understanding the habitat types that support high abundances of animals is critical for effective marine conservation efforts. In this thesis, I focused from the bottom up on areas of high forage fish (capelin, Mallotus villosus) density in Newfoundland and from the top down on areas of high marine predator density in the California Current Ecosystem (CCE). To understand habitat associations of forage fish in Atlantic Canada, I interviewed fishers to map the spatial extent of subtidal spawning sites of capelin, a key foraging area for marine predators and used the interview results to conduct at-sea surveys. In the CCE, I used archived marine bird and mammal count surveys and a variety of statistical and spatial methods, such as zero-inflated negative binomial models and canonical correlation analyses, to examine predator habitat associations and niche partitioning. My findings provide an increased understanding of the factors that influence, and limit, habitat selection of key marine predators and their prey during especially vulnerable life-history stages, including breeding and over-wintering. To continue monitoring capelin subtidal spawning dynamics, future studies in Newfoundland will greatly benefit from establishing professional relationships with fishers as citizen scientists. In the CCE, my results emphasize the need for survey coverage with in-situ oceanography monitors in all four seasons in the highly seasonal CCE. February 2024 Fisheries and Oceans Canada, and the Natural Sciences and Engineering Research Council of Canada.
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