Dissertation/Thesis Abstract

Satellite tracking reveals movement, behavior, and distribution of endangered leatherback turtles in the eastern tropical and southeastern Pacific: Implications for conservation
by Shillinger, George Lewis, Ph.D., Stanford University, 2010, 220; 3395876
Abstract (Summary)

Effective transboundary conservation of highly migratory marine animals requires international management cooperation as well as clear scientific information about habitat use by these species. Populations of leatherback turtles (Dermochelys coriacea) in the eastern Pacific have declined by >90% during the past two decades, primarily due to unsustainable egg harvest and fisheries bycatch mortality. While research and conservation efforts on nesting beaches are ongoing, relatively little is known about this population of leatherbacks' oceanic habitat use and migration pathways.

This thesis examines satellite tracking data collected from forty-six female leatherback turtles, electronically tagged during three field seasons at Playa Grande, Costa Rica, the largest extant nesting colony in the eastern Pacific. The turtles were tracked for 12,095 tracking days with a mean track duration of 263 days, a distance of 8,070 km, and a mean travel speed of 37.7 km d-1. This thesis describes the movements and behaviors of internesting turtles, assesses the predictable effect of ocean currents on a leatherback migratory corridor, characterizes the long-distance leatherback movements in the Eastern Pacific, and examines the influence of mesoscale oceanographic features upon the movements and behaviors of post-nesting turtles.

A total of 1135 days of internesting movements were recorded across three tracking years. High-use internesting habitats were identified for leatherbacks within the Exclusive Economic Zones of Costa Rica and Nicaragua. The core 25% utilization distribution (UD) during the internesting period remained predominantly centered within the marine protected area, Parque Nacional Marino Las Baulas (PNMB). The turtles generally dispersed in a northward or southward direction over the shallow continental shelf framing Costa Rica's Nicoya Peninsula. However, there was considerable interannual variation in the shape and area of the larger UD polygons, driven by variability in the thermal environment. The maximum swimming speeds and distance traveled from the nesting beach occurred during 2007. Significantly deeper and longer dive durations to cooler temperatures also occurred in this year, which may have been in response to warming from the south driven by a strong Costa Rica Coastal Current. Our findings validated the importance of PNMB as a critical habitat for internesting leatherbacks, but also suggested that a latitudinal expansion of the Park is warranted.

After completing nesting, the turtles headed southward, traversing the dynamic equatorial currents with rapid, directed movements. In contrast to the highly varied dispersal patterns seen in many other sea turtle populations, leatherbacks from Playa Grande traveled within a persistent migration corridor from Costa Rica, past the equator, and into the South Pacific Gyre, a vast, low-energy, low-productivity region. Analysis of turtle vertical behavior suggested that turtles maximized swimming efficiency with short, shallow dives during migration through an area of strong zonal currents followed by deeper, longer dives that may indicate searching for prey in the South Pacific Gyre. The southern terminus of the turtles' range (35-37°S) was characterized by high mesoscale activity that may act as a physical mechanism to aggregate their prey, gelatinous zooplankton, but it may also act as a thermal limit to their distribution.

The findings from this thesis elucidate potential areas for mitigating fisheries bycatch interactions, thus directly informing ongoing marine spatial planning efforts and existing multinational conservation frameworks. This information will provide an impetus for focusing future conservation efforts within the leatherback internesting region, migration corridor, and dispersal zone that these analyses have identified in the southeastern Pacific Ocean.

Indexing (document details)
Advisor: Somero, George
Commitee:
School: Stanford University
School Location: United States -- California
Source: DAI-B 71/01, Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Wildlife Conservation, Biological oceanography, Remote sensing
Keywords: Dermochelys coriacea, Endangered species, Leatherback turtles, Pacific Ocean, Pelagic predators
Publication Number: 3395876
ISBN: 9781109587159
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