Date of Award

Fall 12-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Science

Committee Chair

William Graham

Committee Chair Department

Marine Science

Committee Member 2

Jerry Wiggert

Committee Member 2 Department

Marine Science

Committee Member 3

Scott Milroy

Committee Member 3 Department

Marine Science

Committee Member 4

Redwood Nero

Committee Member 5

Christopher Sasso

Abstract

Leatherback turtles (Dermochelys coriacea) are a wide-ranging, oceanic species that feed exclusively on gelatinous zooplankton. Leatherback have been spotted in the Gulf of Mexico (GoM) for several decades and consistently had a high level of interactions with longline fisheries. However, no quantitative studies have been performed to address the spatiotemporal distribution of these turtles in the GoM. This research determines 1) leatherback movements and high-use areas in the GoM, 2) their association with oceanographic features, 3) the distribution and density of two abundant medusae in the northern GoM and any association with biophysical parameters, and 4) the body composition and energy density of a select leatherback prey, Drymonema larsoni.

Satellite telemetry data were analyzed using a switching state-space model (SSSM) and a kernel density estimation to identify high-use areas. The SSSM revealed that foraging behavior was dominant in GoM and two high-use areas were present, one in the northeast GoM, and the second in the southwest GoM in Campeche Bay, Mexico. The leatherback positioning data were compared to physical oceanographic features (sea surface height anomalies, temperature and salinity fronts, ocean currents, divergence and convergence) to investigate their potential influence on turtle movement and space use. The turtle observations were found to be positively associated with sea surface lows and salinity fronts. The distribution and density of scyphozoan species (Chrysaora quinquecirrha and Aurelia spp.), potential leatherback prey items, were analyzed with generalized additive models (GAM) to determine the biophysical parameters that are associated with collection of these jellyfish in the northern GoM. These species were found to be associated with salinity, surface currents, temperature, chlorophyll a concentrations, and distance from shore. Visual observations of leatherback foraging in the northern GoM suggested a preferred prey item of Drymonema larsoni. The selective prey item, D. larsoni, has a similar energy density to selective prey in other known foraging locations, revealing the potential for high energy consumption in the GoM.This research suggests that the GoM is a foraging destination for leatherback turtles. These findings can be utilized for the conservation and management of leatherbacks in these waters.

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