Leatherback tracking in the Western Atlantic

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Author: Karen Eckert, Ph.D.

Affiliation: WIDECAST: Wider Caribbean Sea Turtle Conservation Network
 
The Leatherback Sea Turtle (Dermochelys coriacea) is the largest living reptile, and one of the most migratory of all marine creatures. The NE Atlantic population journeys (generally biannually) from subarctic and temperate foraging grounds to warm Caribbean waters to mate and lay eggs, all the while facing many threats both in nearshore waters and on the nesting beach. Steep population declines over the course of the 20th century resulted in the species being listed on the U.S. Endangered Species Act, several international conservation treaties, and the IUCN “Red List of Threatened Species.”
 
Members of the Wider Caribbean Sea Turtle Conservation Network (WIDECAST), a Regional Activity Network of the UNEP Caribbean Environment Programme, have been working together for more than 30 years to ensure safe passage to Leatherbacks, and all sea turtles, in Caribbean waters. The network is comprised of scientists and educators, natural resource officers, and community-based conservation leaders in 43 Western Atlantic nations and territories – and as a result of this collaboration, sea turtles are fully protected by law in more than 80% of all Caribbean countries; in addition, most major nesting beaches enjoy managed or protected status.
 
Much of what we know of these elusive reptiles comes from painstaking data collection on the nesting beach – or from the use of Argos satellite transmitters to track nesting females during and after the nesting season to determine high use areas and delineate migratory corridors to distant foraging grounds. When questions arose concerning the extent of overlap between the marine habitats used by iteroparous Leatherbacks during the 5 month nesting season and seismic operations planned by Repsol Aruba B.V. off the Dutch Caribbean island of Aruba, WIDECAST (including its local affiliate, Turtugaruba) and Repsol Aruba B.V. turned to Argos satellite-derived location data for help.
 
Because marine turtles hear well underwater, and their hearing sensitivity lies within the envelope of sound produced by seismic sources, the temporal and spatial patterns of habitat use are highly relevant in developing mitigation schemes to avoid impacting the turtles or their inter-nesting habitats. We sought to understand habitat use and high use areas, so that we could evaluate the potential effects on the turtles by seismic exploration in Aruba’s territorial waters. Our methods included the deployment of VHF transmitters and GPS-equipped satellite platform transmitter terminals (PTT) on gravid Leatherbacks when they came ashore to nest on the island’s beaches. This combination of instrumentation allowed both real-time detection of Leatherback locations, as well as high resolution long-term monitoring of movements and habitat use. 
 
With a range of 2.000 m for the transmitters, Repsol developed response protocols requiring all seismic operations to cease if a turtle approached the vessel to within 500 m, (as determined by detection of VHF transmissions) – and to remain so until the turtle cleared the area.  In addition, seismic surveys were avoided within 100 m of the 50 m depth contour around the island, and around all subsurface features that rise to a depth of 50 m from the surface.  Argos satellite telemetry data was then used to evaluate inter-nesting high use areas in territorial waters, and to advise marine resource managers on critical habitats. The objective was to avoid exposing turtles to harmful levels of acoustic sound from the air guns on the acoustic survey vessel, and to avoid displacing turtles from critical habitats, including nesting beaches.
 
Effective mitigation requires that we know where sea turtles are in relation to potential sources of anthropogenic impact, such as during seismic surveys, as well as understand the geography of high-use and other sensitive habitats critical to their survival. Location data from Argos satellite tags are invaluable in this context. The results of the research were presented to the SPE International Conference and Exhibition of Health, Safety, Security, Environment, and Social Responsibility in Stavanger, Norway, in April 2016. When all satellite transmitters have expired, the full extent of the data collected will be prepared for peer-reviewed publication by the research team.