Telemetry Research

Harness image 2   Over the last decade, the Marine Turtle Program at SWFSC has employed wildlife telemetry as a standard research tool to address information gaps identified as priorirties in the Pacific Sea Turtle Recover Plans. This research has focused on all five species occurring in the Pacific Ocean and has yielded substantial information on population (stock) identity, long-distance migration, dive behavior, and habitat use. Among the greatest advances have been the discovery of leatherback migratory corridors that cross the Pacific and an understanding of their habitats. The scientists at the SWFSC have identified the origin of leatherbacks that utilize foraging grounds at the west coast of North America as the turtles from western Pacific nesting beaches (Benson et al. 2007a, 2007b). We have been pleased with these data, as this information has been vital for management purposes and will lead to better management of fisheries in habitat that is important for leatherbacks. . Because the leatherback carapace is soft and covered with skin, transmitters cannot be attached with glue (a common technique utilized to attach transmitters to sea turtles with a hard shell). To solve this challenge, a custom-fitted soft harness with a corrodible link mechanism that limits the attachment duration was developed (Eckert and Eckert, 1986). This technique has been used for nearly 20 years, deployed on leatherbacks around the world. However, we recognize the need for improving this attachment technique. With this in mind, our research strategy with respect to leatherback telemetry deployment has been based on the following four principles. (Photo: Scott Hansen)

1. Does the harness have lasting effects on leatherbacks?

To maximize the safety of these harnesses on leatherbacks, we use a system that has a corrodible link that dissolves over time in the sea water, allowing the turtle to shed the harness after approximately two years. We use antifouling paint to reduce biofouling (barnacle and algae attachment), which increases the weight and drag of the harness system, and soft vinyl tubing at the shoulders to minimize chaffing. Leatherbacks equipped with harnesses and transmitters have been re-sighted at coastal California foraging areas and at nesting beaches after having shed these systems, with no apparent lasting effects (re-sighted turtles have been robust, appeared healthy, and deposited eggs at their nesting sites). During situations when leatherbacks have been re-sighted after two years or less, the harness system has been removed from the animal by biologists at-sea or at the nesting beaches. (Photo: Scott Hansen)  Harness image 3

2. Measure the effect of harness presence on at-sea behavior

flipper tag image 2  

To address this question we have conducted studies on dive behavior of harnessed and non-harnessed turtles at a nesting beach in the Caribbean (Eguchi et al. unpubl. data). A total of ten nesting female leatherback turtles were equipped with time-depth recorders (TDRs), of which five were equipped with a harness and another five without. Preliminary analysis indicated there was no statistical difference in the mean dive duration, mean dive depths, maximum dive durations, and mean dive durations between the two groups. A complete analysis is underway to examine the possible difference between the diving behavior of the two groups. In addition, there have been other studies examining the effects of harness attachment (Fossette et al. 2007; Sherril-Mix and James 2008), and our efforts will complement these studies. (Photo: Tomo Eguchi)

3. Continuously develop new attachment techniques and smaller transmitters

We continue to find better, smaller transmitters, and to innovate more efficient attachment techniques. Over the last 10 years, scientists at SWFSC have worked with several wildlife instrument companies to provide advice on the development of smaller, more efficient tags, which allow for less invasive attachment mechanisms. In a collaborative effort with Dr. James T. Harvey (Moss Landing Marine Laboratories), we began developing and deploying suction-cup mounted TDRs and VHF transmitters in 2004 to study short-term diving behavior and movements of leatherbacks relative to prey fields along the central coast of California. The use of suction cup tagging does not require physical capture of turtles, thereby eliminating the behavioral effects from handling. This technology has also been used to attach video systems to leatherbacks (Reina et al. 2005). In addition to suction-cup techniques, there have been efforts to develop direct attachment to leatherbacks without the use of a harness (Fossette et al. 2007; Witt, Coyne, and Godley unpubl. data), and we look forward to the results of these efforts. In 2006 we reported on the use of a flipper tag mounted micro TDRs for leatherbacks (Eguchi et al. 2006), and this is a technology deserving of further applications. (Photo: Scott Hansen)    Suction cup image 1

4. Hold turtle health as the most important aspect of any study

 Harness image 1  

Biologists from SWFSC continue to set the bar high when it comes to ensuring the health of their study subjects. For example, all capture efforts for leatherback turtles along the central coast of California are accompanied by veterinarian or a veterinarian assistant that monitors respiration and heart rates of captured leatherbacks. We will continue with this protocol for as long as we conduct in-water captures of leatherbacks, and we hope that researchers at other institutions will do the same. (Photo: Scott Hansen)