Sea Turtle In-Water Study Additional Research


In addition to gender, weight and body measurements, scientists also gather keratin (shell scrapings) and several different blood samples from the turtles. These samples are sent to different scientists all over the United States. There is a wealth of information in the samples and the data gathered from them is used in numerous areas of research. Below are brief descriptions of a few of the studies being conducted using these samples.


Sea Turtle Sex Ratios

The Owens lab has been collaborating with the South Carolina Department of Natural Resources in their "In water sea turtle research program". Our roll is to assist in answering the very tricky question of how many male and female turtles there are in the populations of loggerheads, Kemp's ridleys and green sea turtles off the Carolinas. This is a doubly interesting question and not as trivial as it might seem. In the first place, sea turtle sex is not externally obvious. That is they do not exhibit secondary sex characteristics until they reach adulthood, when it is obvious. However since sea turtles may take from 15 to 50 years to reach sexual maturity, and since most of the turtles in the population are juveniles, it is a serious issue. In addition, a quirk of sea turtle biology also adds additional mystery and importance to determining the sex ratio of these difficult to capture animals. The sex of most vertebrates is determined by genetics, as in the genes on human X and Y chromosomes. In sea turtles there is no genetic sex determination; rather, sex is determined by the temperature at which eggs are incubated. As it turns out cool beaches like those in the Carolinas are more likely to produce males while warmer beaches like those in Florida produce many more females (possibly as high as 90% females). Thus, for populations that are threatened or endangered it is of critical importance to know the male and female production in order to be able to model and understand long-term population recovery prospects.

Our lab has a technique which requires a small blood sample to determine the sex. The technique is based on the slight difference in testosterone levels which males have over females as juveniles. Michelle Lee, a graduate student in Marine Biology has been working hard for the past three years in doing the radioimmunoassays for the hormone testosterone. Right now the overall numbers look as if the population of loggerheads is biased toward females by approximately 2:1. All is well for now with a slightly female biased sex ratio, however, if Global Warming continues, a long term concern is that all females might eventually be produced which could spell a catastrophic problem for sea turtles.

Dr. David Owens
Director of Graduate Program in Marine Biology
Grice Marine Laboratory
College of Charleston Graduate School


Comparison of feeding areas to nesting surveys

At the University of South Carolina, we are looking at mitochondrial DNA sequence diversity in samples of individuals inhabiting feeding grounds off the coasts of Georgia and South Carolina. We genotype this feeding aggregation, then compare their genetic 'constitution' against gene frequencies collected from nesting beach surveys. Using statistical analyses, we are able to estimate the contribution of various nesting beaches to the offshore feedings aggregations. The basic message so far from these genetic analyses is that the feeding aggregation is composed primarily of individuals from nearby coastal nesting beaches. We are in year four of this study, multiple years allows us to understand the temporal variation in nesting beach contribution to offshore feeding areas.

Joseph M. Quattro
Director of Graduate Studies, Marine Science Program
Department of Biological Sciences
University of South Carolina


Contaminant levels and turtle health

Environmental contaminants, such as PCBs, pesticides, and mercury, are analyzed in blood samples. Mercury is also measured in keratin scrapings from the turtles' shells. These chemicals are released into the environment by human activities and are known to accumulate in animal tissues. They are commonly found in wildlife, including sea turtles, and if the concentrations are high enough, they are known to produce toxic effects. Knowing the concentrations in the sea turtles from the southeast coast of the U.S. is important so that we can compare the concentrations to indicators of health, such as white blood cell counts, blood chemistry values, and immune system functions.

Jennifer Keller
National Institute of Standards and Technology
Hollings Marine Laboratory
Charleston, SC


Vitamin D Study in Sea Turtles at the New England Aquarium

This project involves the investigation of captive, wild and rehabilitated sea turtles for plasma levels of vitamin D. Vitamin D levels have been shown to be critical for development of young turtles and healing processes. To date research has not been conducted on serum vitamin D levels or UVB spectrum lighting requirements in sea turtles. Two unique collaborative opportunities have availed themselves this year. These opportunities include obtaining plasma from wild sea turtles in South Carolina with Dr. Al Segars from the SC Department of Natural Resources and analysis of serum vitamin D levels at Boston University School of Medicine with Dr. Holick

This novel investigation will provide critical data for UVB spectrum lighting requirements for sea turtles held in captivity for display, head start, and rehabilitation programs. Understanding this nutritional need may also greatly enhance the healing process for injured sea turtles and allow for proper growth and development for head-start sea turtles. The wild sea turtle survey work is necessary to provide normal serum vitamin D levels in apparently healthy populations of sea turtles.

Dr. Leslie Boerner Neville
Associate Veterinarian
New England Aquarium
Boston, Massachusetts

Publication of Project Oceanica.
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