Background

Leatherback turtles are regular visitors to the US east coast, seasonally migrating into productive coastal and shelf waters to forage on gelatinous zooplankton. Their annual presence suggests favorable foraging conditions during certain times of the year, although the environmental cues which determine their arrival, departure and movements in the shelf region remain unknown. Despite significant progress in the management of pelagic fisheries with respect to sea turtle by-catch, the impact of coastal fisheries on leatherback populations remains poorly studied. Identifying areas and times of likely interaction between coastal fisheries and leatherbacks will benefit management decisions for these fisheries and may help reduce fishery impacts on leatherbacks foraging and migrating along the US east coast.

Current research

Our research utilizes state-of-the-art telemetry devices to record the behavior and movement of leatherback turtles both around the nesting beaches and at the foraging grounds.

The satellite tags we use transmit depth, temperature, and location information via the Argos satellite system. When the tag breaks the surface of the water, data are transmitted to polar orbiting satellites and relayed to us in near real-time. We've programmed our tags to transmit frequently on a daily basis in order to capture “fine scale” (high resolution) movements. The GPS-linked satellite tags provide both Argos-derived positions as well as positions with GPS precision (accurate to +/- 55m).

This is the first time these tags have been deployed on leatherback sea turtles in the Atlantic and the data is allowing us to gain a much needed insight into the fine scale movements of turtles in a region rarely studied by researchers in the past. We are analyzing these movement data in relation to physical and biological oceanographic conditions as well as the location of various near-shore fisheries which operate in the area.

Attaching instruments to leatherback sea turtles is challenging. The leatherback shell is covered by thin black skin which precludes the use of glue to attach devices (a technique routinely used on hard-shell sea turtles). Although most studies have used a harness to attach devices to leatherbacks, direct attachment to the carapace is rapidly becoming the attachment method of choice for researchers worldwide. By attaching directly to the carapace the footprint of the system is minimized, reducing drag and discomfort to the turtle.

While attaching devices to leatherbacks we also take a small (4 mm) skin biopsies from the turtle. These samples will be used to determine the stock origin of leatherbacks in the US east coast foraging grounds as well as provide information on the likely prey of these turtles. This is achieved through stable carbon (13C) and nitrogen (15N) isotope analysis - a technique which tells us the atomic composition of the skin which can then be compared to the atomic composition of likely prey species collected in the field.

To date, seven leatherbacks have been tagged with GPS-linked satellite tags. During March of 2007, two tags were deployed on leatherback turtles off of the north Florida coast. In summer and fall of 2007, five tags were deployed on leatherbacks off of Cape Cod , Massachusetts . Blood, skin and cultures were collected for health, genetic and stable isotope analyses of live leatherbacks. Skin, muscle and liver were collected from dead stranded leatherbacks for genetic and stable isotope analyses. Gelatinous zooplankton associated with leatherbacks was documented and collected off of Cape Cod and the southeast U.S.

Additional deployments are planned for both the southeast US and Cape Cod in 2008.

Our research also extends to the nesting beach where, in May 2007, we attached several archival data loggers to nesting female leatherbacks on St Croix in the US Virgin Islands. These ‘Daily Diary' devices were recently developed by our colleagues at the University of Wales in Swansea , UK and record several different parameters at the same time allowing us to reconstruct several aspects of the movement and behavior of the animals whilst at sea. As well as recording temperature and depth these devices also record speed, compass heading, acceleration (on three axes) and mouth opening behavior.

As well as allowing us to record dive frequency, foraging effort, breathing frequency and a host of other behavioral characteristics these tags also allow us to calculate a relative measure of energy expenditure. By combining the extracted dynamic acceleration (acceleration caused by movement) from the three acceleration channels we are able to quantify the movement of the animal. This same method was used on cormorants in a respirometry chamber, and the overall dynamic body acceleration was found to be a reliable proxy for energy expenditure. Unfortunately, at present, we are unable to conduct a similar calibration with a leatherback turtle in a respirometry chamber. However, we are able to obtain a relative measure of energy expenditure.

We are hoping to further this work by attaching daily diary devices to leatherback turtles at the foraging grounds to allow us to conduct a much needed comparative study between these two distinct regions.

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Current projects and collaborators:

•  Leatherback sea turtle health study: New England Aquarium

•  Leatherback sea turtle disentanglement and satellite tagging: Provincetown Center for Coastal Studies

•  Biological sampling from dead stranded leatherback sea turtles: Northeast Region Sea Turtle Stranding and Salvage Network

•  Leatherback sea turtle energetics and thermal biology in the northwest Atlantic: University of North Carolina, Wilmington

•  Leatherback sea turtle 3-dimensional movements and behavior during the inter-nesting interval, St. Croix, USVI: University of Wales, Swansea and West Indies Marine Animal Research and Conservation Service

All leatherback research is conducted under the authority of NMFS Permit Number 1557-03

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