The Influence of Environment on the Foraging Strategies of Cetaceans

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2022

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Abstract

The processes of locating and capturing food are critical components of a predator’s fitness, but can be difficult to observe, particularly in marine environments where foraging behavior is not often visible from the surface. Individuals and populations display a range of foraging adaptations, from stenophagous individuals who consume a single prey type to generalist populations that thrive with a variety of environments and prey taxa. Populations and individuals that show high levels of behavioral plasticity may be able to alter their foraging behavior when environmental conditions change, demonstrating new foraging strategies depending on the characteristics of the habitat and local prey fields. In this dissertation, I used high-resolution data from bio-logging tags deployed on three well-studied species of cetaceans (whales and dolphins) in novel environments, to analyze the role of environment in cetacean foraging strategies and kinematic behaviors. Bio-logging tags provide high-resolution information about predator foraging ecology, including foraging rates, kinematics of prey capture attempts, and even interactions between predators and prey. I first analyzed tag records from short-finned pilot whales (Globicephala macrorhynchus) foraging near the shelf-break off Cape Hatteras, North Carolina. In this analysis, I sought to determine if pilot whales forage near the seafloor when it is within reach, and whether such behavior affects their foraging rates and diel patterns. I tapped into the whale’s own sensory system, using the echoes of the animal’s echolocation clicks bouncing off the seafloor to demonstrate that many whales frequently foraged near the seafloor itself. I then used high-resolution kinematic data to investigate how benthic foraging affects the fine-scale details of prey capture attempts. Tagged whales were often upside-down while foraging benthically and appeared to pursue benthic prey as they attempted to escape by swimming away from the seafloor and into the water column. I used similar methods to study the foraging behavior of the offshore ecotype of common bottlenose dolphins (Tursiops truncatus) in pelagic waters near Bermuda. These offshore dolphins dive to considerable depths; I analyzed the effect of depth on the energetics and capture success rates of foraging attempts. I was able to eavesdrop on the echolocation clicks produced by dolphins during prey capture attempts to estimate the distance from the dolphin to its prey, and determine whether prey captures were successful. Dolphins foraging in deep dives encountered more prey and foraged with higher success rates than while foraging near the surface. Finally, I studied the fine-scale kinematics of humpback whales (Megaptera novaeangliae) foraging in winter feeding grounds near Virginia Beach, Virginia to determine how this extremely shallow water environment affected their foraging behavior. Humpback whales lunge-feeding in this area have limited maneuverability, likely due to the shallow nature of the environment, and exhibited simplified kinematics compared to studies in other areas. Nevertheless, these whales were still able to forage at high rates, with some evidence of higher foraging attempts made at dawn. The foraging ecology of these three species has been extensively studied elsewhere, but new environments present opportunities to discover novel foraging strategies. Overall, my dissertation illustrates the ways in which environmental features shape foraging behavior in these three species of behaviorally plastic cetaceans.

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Shearer, Jeanne Michelle (2022). The Influence of Environment on the Foraging Strategies of Cetaceans. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/26869.

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