Sea turtle nesting on Eglin Air Force Base property, Cape San Blas, Florida

Science Center Objects

The Northwestern Atlantic population of loggerhead sea turtles is one of the largest in the world. Genetic studies have divided this population into 5 management units including a genetically distinct group that nests throughout the northern Gulf of Mexico (GoM).

Observed and estimated Loggerhead sea turtle abundance

Fig. 1. Observed and estimated Loggerhead sea turtle abundance on Eglin Air Force Base property, Cape San Blas, Florida between 1998 and 2011.

The Science Issue and Relevance: The Northwestern Atlantic population of loggerhead sea turtles is one of the largest in the world. Genetic studies have divided this population into 5 management units including a genetically distinct group that nests throughout the northern Gulf of Mexico (GoM). This northern GoM group is the second smallest with an estimated 323-625 individual; Dry Tortugas is the smallest. Eglin Air Force Base (EAFB-CSB) property on Cape San Blas, FL supports one of the densest nesting assemblages for this northern GoM management unit. Nest numbers along EAFB-CSB have experienced severe declines since 1995 (see Figure; dotted lines are confidence intervals). Understanding population structure, impacts from anthropogenic threats, and demographics of these individuals is necessary for effective management of this distinct nesting group.

Methodology for Addressing the Issue: Morning surveys for nesting activity are conducted from May 1 to November 1 each year; these surveys have occurred since 1994. Nightly, saturation tagging surveys for nesting females are conducted every night from June 1 to August 1; these mark-recapture surveys have occurred since 1998. When a nesting turtle is located, it receives a flipper tag in each front slipper and a Passive Integrated Transponder (PIT) tag in its shoulder. Morphometrics are collected and biological samples including blood, skin and carapace, are taken. To assess spatial habitat use, a subset of nesting females receive tracking tags including satellite tags and accelerometers.

Fig. 2. Loggerhead sea turtle, Cape San Bas, FL

Fig. 2. Loggerhead sea turtle, Cape San Bas, FL

Nesting data provide information on reproductive output and a better understanding of the factors driving nesting phenology. They are also used to assess the impacts of various anthropogenic threats to nesting sea turtles such as marine debris. Mark-recapture data will contribute to the development of accurate abundance estimates, and demographic rates including remigration interval, interesting intervals, growth and survival. Biological samples are contributing to genetic studies to better understand the population structure of the Western Atlantic population. In addition, they are used for stable isotope analyses that provide information on foraging requirements. Satellite tracking provides the only information available of spatial habitat use for this nesting group. This identifies ‘hot spots’ for managers to target for future conservation.

Future Steps: Continuation of the long-term nesting surveys and mark-recapture analyses will allow for improved accuracy in current demographic estimates. Expanding these surveys to include genetic mark-recapture (using one egg from each nest deposited in Northwest Florida) may help reduce nightly tagging efforts and also improve estimates. Analyses of biological samples will provide further clarity to questions of population structure and impacts of anthropogenic threats.

Related Project(s) and Product(s):

Eglin Air Force Base sea turtle tagging