Sea Turtle Tracking: Results of 1994 and 1995 Migration-Tracking of Florida Green Turtles

Results of 1994 and 1995 Migration-Tracking of Florida Green Turtles

During the 1994 sea turtle nesting season, researchers Barbara Schroeder with the Florida Department of Environmental Protection’s Marine Research Institute, Dr. Llewellyn Ehrhart with the University of Central Florida and George Balazs with the National Marine Fisheries Service attached satellite transmitters to three green turtles that nested in the Archie Carr National Wildlife Refuge. The three turtles — named Honu, Fairly and Keya — became part of a unique research project designed to help discover the unknown migratory patterns of green turtles nesting in Florida.

After attaching the transmitters, researchers studied locational data sent back through the Argos satellite system. At the 1995 Sea Turtle Symposium in Hilton Head, South Carolina, the preliminary findings were presented by Schroeder in a paper coauthored by Ehrhart and Balazs. The following short summaries of each turtles’ movements are based on data presented at the symposium:

Fairly – Tag #22127

Tagged on July 23, 1994, Fairly’s transmitter sent signals until October 15. On August 13, she was seen nesting again in the Archie Carr Refuge (green turtles are known to nest 3 or 4 times a season). After having nested again, signals located her off the coast of Ft. Lauderdale. After another 13 days, she had made it to an area off the lower Florida Keys known as Coffins Patch Reef, where she stayed approximately 50 days until signals were no longer received. The habitat in this area is characterized as patch reef with fragmented seagrass meadow.

Keya – Tag #22128

Tagged on July 22, 1994, signals were received from Keya until late October. From July 22 through Sept. 5, all of Keya’s signals were sent from the vicinity of the Archie Carr Refuge. On Sept. 8, her signal began to illustrate a southward migration, and by Sept. 16 she had reached the coastline near Key Largo, Florida. Her final signal, received Oct. 21, showed her stationary off the Marquesas Keys located at the southern tip of the Florida Keys. The habitat here is also characterized as patch reef and seagrass meadow.

NOTE: Keya was seen nesting again on 13 August, 2000.

Honu – Tag #22129

Tagged on July 21, 1994, Honu’s transmitter did not function long enough to document any movement away from her nesting beach. Signals ceased after 30 days, during which time she stayed in the immediate vicinity. The last signal was received Sept. 9, 1994.

After the study, the research team made a preliminary hypothesis that Florida green turtles utilize reefs and seagrass meadows around the Florida Keys as their primary feeding grounds. However, because of the short duration in which signals were received, more study was needed.

A similar experiment was conducted during the 1995 nesting season. This time, the turtles’ movements were tracked for longer periods of time, and the results provided new insight into the migration of Florida green turtles. Some of the turtles tracked during 1995 followed a similar course toward the Florida Keys. However, at least one green turtle migrated to the Bahamas and travelled throughout the islands until her transmitter stopped working.

STC was very interested in seeing this research continue and tracked four green sea turtles in 1996 with the assistance of Snapper, Inc., the Educational Foundation of America, the Geraldine R. Dodge Foundation, the Blue Planet Foundation, University of Central Florida, and the Florida Department of Environmental Protection. STC would like to thank Barbara Schroeder at the National Marine Fisheries Service, Andrea Mosier at the Florida Marine Research Institute and Dr. Llewellyn Ehrhart and his students at the University of Central Florida for funding, tagging the sea turtles and providing the location maps. See the results of the 1996 tracking.


Results of 1995 Migration-Tracking Research in the Caribbean

The new technology of satellite telemetry has made it possible for researchers to study effectively for the first time the migratory habits of male green turtles in the Caribbean.

Because males do not leave the water (except occasionally — to chase a fleeing female through the surfline!), they don’t readily lend themselves to observation, and they are rarely tagged. Consequently, next to nothing is known about their movements and biology.

Tagging studies at Tortuguero conducted by STC have produced a large and valuable body of data about the reproductive biology and migrations of the female green turtle. However,rough and turbid sea conditions throughout most of the nesting season have discouraged investigations in the waters off the nesting beach. Until recently, most of the information on Tortuguero males has been gleaned by Costa Rican scientists during visits to the turtle slaughterhouse in Limon.

Since 1990, STC associates Peter and Anne Meylan have been studying the green turtles that pass seasonally through the waters of Bocas del Toro Province, Panama, approximately 150 miles southeast of Tortuguero. Locals in Bocas have traditionally fished for green turtles for centuries. The timing of the appearance of turtles in Bocas, the recovery of Tortuguero tags in Bocas and of Bocas tags in Tortuguero, and genetic data, all suggest that the green turtles the Meylans catch each year are members of the Tortuguero population.

The migrants are caught in large-mesh tangle nets, measured, tagged and released. Although there have been more than a dozen long-distance recoveries of turtles tagged in Bocas, the actual routes and schedules of migrations of the turtles tagged there have remained unknown.

In July 1995, two breeding males captured in Bocas were outfitted with satellite transmitters. The ST6 units, made by Telonics, were fiberglassed directly onto the back of the carapace, behind the head, where the unit’s small flexible antenna can break the surface and transmit when the turtle comes up to breathe. The transmitters send information to passing satellites about the position of the turtle, the number of dives during the last 12 hours, the length of the last dive, and the temperature. The satellite re-transmits the data to France, where it is relayed to the United States and can be accessed by computer. The coordinates can then be plotted on maps, and the position and travel route of the turtle can be determined.

Analysis of the satellite data suggests that these two males did not behave as researchers expected. Current life history models predicted that they would proceed to Tortuguero with the females, and remain there for mating purposes in the near shore waters. They would eventually head back to their resident feeding grounds, which in the case of migrants captured in Panama, would be in the direction of South America. Neither turtle followed the model. The Meylans are now evaluating other hypotheses to explain the movements. The plotted movements of both turtles can be seen at right.

One of the turtle’s (the blue track on the map) transmitter continued to send signals until around the end of September, when data began showing no more dives below the water’s surface. Eventually, it was determined that the signals were coming from a remote section of the Panama coast, where extensive net fishing for turtles is known to occur. After a very interesting search, the transmitter was recovered from the fisherman who had caught the turtle, and it was confirmed that the turtle had been butchered.

The other turtle (the red track on the map) was tracked until the end of November. After moving a short distance offshore, the turtle moved north and seemed to circle off the Costa Rican coast near Tortuguero –probably searching for females. Eventually, the turtle traveled still further north to the well-known green turtle feeding grounds at the Miskito Cays off Nicaragua.

The project was funded last year by the Wildlife Conservation Society; technical support was provided by the U.S. Fish and Wildlife Service. With the help of STC, the Meylans are working to plan and fund additional research to be conducted later this year on turtles around Bermuda. As the project proceeds, the migration data will be posted and regularly updated on a map at this web site. We invite you to check back regularly to watch the movements of these and other turtles being tracked by satellite.