Graduation Year

2012

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Edward S. Van Vleet

Co-Major Professor

Anton D. Tucker

Keywords

Environmental Cues, Infrared Thermometer, Reproductive Biology, Sediment, Temperature, Thermocouple Probe

Abstract

Many environmental cues are thought to influence nest site selection by loggerhead sea turtles, Caretta caretta, and much debate exists over the possible influence of sand temperature. This study had two primary objectives: (1) to measure thermal differences across transects of a major nesting beach of Casey Key (28.7 N, 82.3 W), Florida and (2) to evaluate thermal pattern variation that influenced nesting patterns of adult female loggerhead sea turtles. A secondary objective of this study was to determine the efficacy of infrared thermometers to collect sand surface temperatures in the field.

Temperature data were collected from 145 nest events and 8 false crawls in the 2008 and 2009 nesting seasons. Infrared thermometers and thermocouple probes were used to obtain surface temperatures from the water, waterline, beach sand, body pit attempts, nest chamber attempts, eggs, and the surface of the gular skin of the nesting female, within the crawl track created by the female and at one meter adjacent to the crawl track (from undisturbed sand). Weather influences at the time of nesting were recorded, including the presence or absence of rain, wind, or clouds. Beach slope was measured using an angle locator.

Temperature data from the infrared thermometer and the thermocouple probe were highly correlated, indicating that an infrared thermometer is an effective measurement tool on a nesting beach. In 2008, there was a significant difference between temperatures collected within the crawl tracks of false crawl events and nest events, indicating a potential for females to use thermal cues in choosing whether to false crawl or nest. In both nesting seasons, the sand temperature in the body pit and the surface of the gular skin of the nesting female were nearly identical, suggesting females may locate a suitable nest site using their skin temperature. Data collected at other loggerhead rookeries in the United States and Australia yielded similar results, however, variability in the use of temperature may arise seasonally, and according to different nesting environments.

Rain, wind and cloud cover significantly thermally altered several locations on Casey Key, but it remains unclear if these weather events significant affect turtle nesting behavior. Additionally, crawl distance and beach slope were significantly, positively correlated.

Gravid females most likely use multiple environmental cues to select a nest site. Assimilating information from multiple sources allows for the highest degree of adaptability, and future studies should consider implications for climate change and beach renourishment projects.

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