How Oceanography Influences The Foraging Behavior Of A Twilight Zone Predator, The Elephant Seal

• Main Author: Keates, Theresa Rebecca
• Other Authors: Costa, Daniel P
• Format: Other/Unknown Material
• Language: English
• Published: eScholarship, University of California 2022
• Subjects: Biological oceanography; Physical oceanography; Biology; biologging; elephant seal; foraging behavior; mesopelagic; mesoscale features; Elephant Seal; Elephant Seals; Mirounga leonina; Southern Elephant Seals
• Online Access: https://escholarship.org/uc/item/5rm2z0x5

In a rapidly changing ocean that remains largely undersampled, physical and biological observations are crucial to understanding, predicting, and mitigating effects of anthropogenic stressors. Animals instrumented with oceanographic sensors offer valuable supplements to datasets from more traditional oceanographic methods while simultaneously offer information about the oceanography of areas significant to the animals. Marine predator foraging behavior relative to physical or biological features such as fronts, eddies, and phytoplankton blooms can be used to infer oceanographic influences on the distribution of pelagic prey. This dissertation applies tracking data from adult female northern elephant seals (Mirounga angustirostris) and southern elephant seals (Mirounga leonina) with in situ temperature, salinity, and chlorophyll fluorescence collected by instruments carried by the seals to investigating relationships between oceanographic features and the foraging behavior of these wide-ranging mesopelagic predators at basin- to submesoscales. Chapter 1 investigated the behavior of northern elephant seals when they encountered eddies. This project used a 17-year dataset of time-depth recorders and concluded that while eddies are a minor feature of their habitat, seals do derive foraging benefits from both cyclonic and anticyclonic eddies. Our observations suggest that physical prey aggregation is a more likely mechanism making eddies beneficial to foraging seals than bottom-up energetic enhancement of the food web resulting from nutrient injection. Chapter 2 combined tracking data from northern and southern elephant seals to compare their behavior relative to the oceanographic conditions they encountered. This first direct comparison between the at-sea behavior of these two closely related species showed comparable movement and diving behavior and further, very similar relationships between behavior and temperature, salinity, and mixed layer depths encountered. Both seal populations were more responsive to ...