DISSERTATION RESEARCH: Fine-Scale Pelagic Predator-Prey Interactions: Hawaiian Spinner Dolphins and the Mesopelagic Boundary Community

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"Fine-scale pelagic predator-prey interactions:Hawaiian spinner dolphins and the mesopelagic boundary"Whitlow W. L. AuDoctoral Student: Kelly J. Benoit-BirdSpinner dolphins in Hawaii feed at night on small fish, shrimp, and squid. Their prey is very deep during the day but migrates close to the surface and near the coastline every night. Spinner dolphins follow the movements of their prey. They move inshore and offshore along with their prey's migration and they dive to the depths at which their prey is most abundant. Spinner dolphins also forage specifically on high-density prey patches, small areas that have more prey than those around them do. Other studies of pelagic predators, however, have not shown this type of overlap with prey. Data will be collected on both spinner dolphin predators and their prey simultaneously using scanning sonar, a device that will allow the location and abundance of predator and prey to be plotted in three-dimensions. Foraging dolphins will be tracked from a boat with the scanning sonar and the density and geometry of prey patches will be measured. Changes in these characteristics will be observed as the dolphins forage to observe how they affect the behavior of their prey. Dolphins probably use echolocation, a natural sonar system, to find their prey. How this system is used by animals in the wild to forage has however, not been studied. To begin to understand echolocation's role in foraging, the rate of echolocation clicks, individual sonar signals, will be measured while measuring the distance of the dolphins from their food. If spinner dolphins are using echolocation to find their food, the number of clicks and their production rate should increase as dolphins get closer to their prey. This work will determine if pelagic predators can overlap with their prey at small scales, which behaviors allow this to happen, and what role echolocation plays in dolphin's search for food.