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In this brief note, we report on the effect of a prolonged harness deployment on a leatherback turtle, which returned to nest after a two-year period with the harness still attached. We also provide recommendations for future leatherback telemetry studies using harnesses as the transmitter attachment method.

On June 7, 2003, a nesting leatherback was fitted with a harness and KiwiSat transmitter on Tortuguero Beach, Costa Rica, as part of a collaborative project between Hubbs-Sea World Research Institute (HSWRI), Caribbean Conservation Corporation (CCC) and the University of Central Florida (UCF) (see front cover). The harness used in this project was based on one long used by S. Eckert (Eckert 1998; Eckert & Sarti 1997; Ferraroli et al. 2002; James et al. 2005a) and others (e.g. James et al. 2005b). The essence of the design involves two vinyl covered straps made of webbing that lace over the shoulders and are connected to a strap that encircles the turtles midsection (= “waist strap”). The end of the straps meet dorsally at a central elastic ring equipped with D-rings for ease of adjustment. The straps, transmitter platform and transmitter were painted with anti-fouling paint of the brand Interlux UltraKote (copper level 76%). While the harness was based on the Eckert design and built by individuals trained by Eckert, this harness had some dissimilar features, in particular, the reduced size of the dorsal elastic ring and the type of connector inside the elastic ring.

The female was encountered on the 9th April 2003, approximately 1 km north of Jalova lagoon at the southern end of Tortuguero National Park, Costa Rica and the satellite tag attached. The turtle renested again approximately 65km south of the release site before beginning a northerly migration. The final transmission was received on January 25, 2004 when the turtle was located off the northeastern seaboard of the USA. A map showing the movements of the turtle named “Chica Tica” following release is available at <http://www.cccturtle.org/sattort_chica-tica.htm>.

Almost two years later, on April 2, 2005 the leatherback nested again at Parismina, Costa Rica, approximately 7 km south of the transmitter attachment location. Nesting behavior was normal and the turtle deposited 77 normal eggs and 14 yolkless eggs. Excavation of the nest after hatchling emergence revealed that nine eggs produced hatchlings that emerged from the nest, 24 eggs had partly or completely developed embryos but did not hatch, 10 eggs died without producing visible embryos and the remaining 34 eggs were depredated. The emerged hatchlings and embryos show that the still attached harness had not impeded the female leatherback from successfully mating prior to emerging to nest.

Asociación Salvemos las Tortugas coordinates sea turtle monitoring and conservation efforts in Parismina. Their staff observed the harnessed leatherback and quickly informed their team leaders who arrived to observe the turtle. Portions of the harness were covered in ectobiota, mainly barnacles but also small crabs and algae. The transmitter and transmitter platform (1/4” plexiglass plate) were almost completely covered with ectobiota and had shifted slightly to the right from its original position. The webbing was significantly less affected by ectobiota and it remained similar to the original attachment position. The central hub of the harness, which is made up of elastic cord covered by silicon tubing, was embedded into the central carapace ridge at two places, to depths of approximately 8 cm and the waist strap and stainless steel rings used to attach the strap to the central hub had become encrusted into the skin. The waist strap had cut into the turtle several cm at the lateral ridges. Once the harness was detached by cutting the silicon tubing and elastic cord, it was easily removed. Soft tissue and skin fragments were exposed where the harness had pushed against the carapace. The vinyl tubes which encase the shoulder straps, and to which the transmitter platform was attached had rubbed against the skin on the shoulders and front flippers and caused callusing. Detailed observations of the turtle and harness were made possible by A. Díaz-Merry, J. Ordoñez and J. Taylor, who encountered the animal on the beach and documented its condition. After completing nesting, the turtle returned to the sea. Once the ectobiota had been removed from the transmitter, it resumed functioning, though the unit was not re-deployed.

The same turtle was observed a second time in Parismina, on April 12, approximately 3.6 km to the south of the April 2 nest site. The turtle had already nested when encountered and returned to the water at midnight. The beach patrollers recorded the flipper tag numbers and also noted that the turtle presented scarring on the central ridge and on the lateral ridges. They did not observe any open wounds, ten days after the harness had been removed. By her third nesting (depositing 85 normal and 35 yolkless eggs on May 1, 2005, north of the Pacuare river, and approximately 15 km south of original transmitter attachment location) no injuries were recorded by the observers so it is probable that the harness injuries had healed rapidly.

Leatherbacks and other species of sea turtle are classified as Endangered or Critically Endangered on the IUCN Red List (IUCN 2004), Critically Endangered in the case of the leatherback, and any researcher working with these species must be extra careful in considering the well being of the individual animals. We believe there are several lessons about attaching instruments to leatherbacks to be learned from this long-term return. It is possible that the harness had been applied too snugly, that the elastic ring was too small to accommodate the subsequent weight increases characteristic of these animals during non-breeding seasons (James et al. 2005b), that the strapping material used for the belly and shoulder straps had constricted over time, and/or that there were design problems in the flexible hub and the link used to hold the hub together. The hub on this particular harness did not include a link designed to corrode over time; however the effects of the harness were observed within the planned lifetime of harnesses designed to fall off after approximately two years. It is possible that superficial carapace damage is difficult to avoid completely when harnesses remain attached to leatherbacks for long periods of time. A total of five leatherback turtles were fitted with the same type of harnesses in Caribbean Costa Rica in 2003 and 2004. Given the normal remigration interval of 2-3 years, we expect these turtles to return to nest during the 2006 and 2007 nesting seasons. Additional lessons regarding the effect of the harness may be learnt from observing these animals when they return to the nesting beach.

A variety of steps have been taken to eliminate the potential problems in harness attachments. The original designer of such harnesses (S. Eckert) has been consulted to help determine if differences in this harness design and/or application may have contributed to the problems observed, and whether other leatherbacks encountered after long-term harness attachments have exhibited similar conditions. These consultations have led to increases in harness flexibility and a lengthening of the elastic ring to reduce tension and pressure on the carapace as well as to allow for growth by the turtle; a change in antifouling paint to Interlux Micron 66 for more effective coatings and better application to all the straps, transmitter platform and transmitter; the use of a corrodible link to limit retention and more detailed guidelines and criteria on harness application procedures for others who may wish to adopt the harness technology. The platform used to mount the equipment has been widened to further avoid impact to the dorsal ridge. S. Eckert is producing a review of his harness use on leatherbacks encompassing the last 20 years, which will include the more detailed guidelines, so that such experience can be shared with others.

Recommendations: To make sure leatherback turtles are only harnessed when absolutely necessary, we recommend that research projects have clear and feasible research and conservation objectives that will be met by the information generated from the telemetry study. We also believe that rapid and transparent reporting of any events where leatherback turtles have been injured by research methods of all types is absolutely paramount so that other researchers are aware of the potential pitfalls and designers can work to improve application protocols.

Comparison of the short and long-term effects of transmitter harnesses with other attachment techniques, such as carapace drilling and bone screws, is desirable so that the least damaging method for attaching transmitters to leatherback turtles can be determined.

On a positive note, the harness and transmitter attachment to “Chica Tica” did not impede the turtle from migrating to the North Atlantic (minimum return distance 9,000+ km), successfully foraging, mating, and returning to lay fertile eggs at least three times with normal renesting intervals at her usual nesting site within a conventional two-year remigration interval. Also, based on the subsequent observation of this individual on April 12 and May 1, 2005, the damage sustained by the female appears to have quickly begun healing once the harness was removed. We believe that any permanent damage to the turtle from the harness and transmitter is unlikely in this case. However, if the female had not been recaptured and the harness removed, her ability to migrate, forage and mate could have been affected.

Acknowledgements: Hubbs-Sea World Research Institute (HSWRI) provided the funding for the transmitter, harness and satellite time for this project. Carlos Drews (WWF), Andy Myers and an anonymous reviewer provided useful comments on draft versions of this contribution.

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