Hermes Heads West

Sea Turtles can be caught, incidentally, in longline fishing gear throughout the world. Understanding the impacts of capture on their physiology and movements will help us develop methods to reduce interactions with long line gear and incidental capture, thus improving survivorship. Since 2005 PIFSC’s Yonat Swimmer of the International Fisheries Program has been collaborating with partners in the Southwest Mediterranean Sea to compare blood biochemistries and movements of turtles that had been caught and released from fishing gear to a control group that had been free-swimming prior to capture. The global collaboration includes scientists from NOAA Pacific Islands Fisheries Science Center, Alnitak, Kai Marine Services, Submon, and University of North Carolina Wilmington. A Norwegian fishing vessel, Toftevaag, was retrofitted to serve as a platform for sea turtle and marine mammal research in the Mediterranean Sea. The Toftevaag was skippered by Kai Marine Service’s Ricardo Sagarminaga van Buiten.

Figure 1. Location of Hermes while satellite tag was active.

Figure 1. Location of Hermes while satellite tag was active.

On July 19, 2012, a loggerhead turtle was spotted on the surface of the water and brought on board the Toftevaag by Ricardo and crew. The turtle, named “Hermes”, measured 74 cm curved carapace length (CCL). It was released at the same day with satellite transmitter affixed to the carapace. Satellite communication through the Sea Turtle Analysis Tracking Tool (STAT) confirmed Hermes location 89 days after its initial release (Figure 1). The last transmission received was on October 16, 2012. At the time the team though all further information from Hermes was at an end. On April 29, 2014, more than a year and half after its last transmission (actually 565 days), Hermes (Figure 2) was found entrained into the Florida Power & Light St. Lucie Nuclear Power Plant intake canal in St. Lucie County, Florida. Biologists with Inwater Research Group found Hermes after it had made the journey out of the Mediterranean across the Atlantic and into the Florida power plant’s intake canal (Figure 3).

Figure 2. Hermes with nonfunctioning satellite tag still attached upon capture in Florida.

Figure 2. Hermes with nonfunctioning satellite tag still attached upon capture in Florida.

St Lucie Nuc power plant

Figure 3. St. Lucie nuclear power plant and intake canal.

The St. Lucie power plant commonly entrains sea turtles that frequent the nearby reefs and nesting beaches adjacent to the plant’s intake canal. Biologists working for Inwater Research Group (IRG) remove turtles from the canal, assess their health, take body measurements and note any distinguishing marks that could aid in recognizing them in future, and tag the animals before safely releasing them. Since 1976, the project has captured nearly 16,000 sea turtles. Upon capture at the intake canal, Hermes appeared healthy and measured 78.6 CCL, suggesting a growth of ~ 2.6 cm in a 21 month period. New flipper tags and a passive integrated transponder or PIT tag were applied to Hermes and it was released back into the ocean to continue its journey. Loggerheads in the same size class as Hermes are commonly captured at the power plant throughout the year. They are frequently sighted by divers and fisherman in the coastal waters of Florida and are the most common species in the region. Many of these loggerheads will migrate seasonally along the Atlantic seaboard of the U.S. from as far north as Massachusetts, south to the Florida Keys and northern Caribbean. As hatchlings, loggerheads leave the beaches of Florida and enter the North Atlantic gyre following the Gulf Stream up the Atlantic coast of the U.S., across the Labrador current and then south along the coast of Europe (Figure 4). They’ll spend many years and cross many miles of ocean in this pelagic environment until eventually migrating to shallower coastal waters that provide benthic developmental habitat where most will stay until they reach maturity. Tags from other turtles in this study have shown loggerheads leaving the Mediterranean Sea to spend several months on the east side of Gibraltar feeding on the shelf. Hermes is unique because this is the first record of a turtle coming from the Mediterranean Sea and making the transatlantic crossing before being captured in Florida. This represents the longest known migration of a sea turtle captured at the power plant’s intake canal.

General turtle migratory path

Figure 4. General migratory paths for marine turtles in the Atlantic (BBC 2008)

Hermes, if a female, with a straight carapace length (SCL) of 72.5 cm might be a bit small to be nesting on a Florida beach because loggerheads of this size class are rarely reproductively active. However, according to University of Central Florida (UCF) assistant professor Dr. Kate Mansfield there are records of females as small as 69.0 cm SCL nesting on beaches in this region. Kate and her team at UCF’s Marine Turtle Research Group will look for Hermes as they monitor nesting activity at the Archie Carr National Wildlife Refuge this summer. As for Hermes’s transatlantic crossing, at a minimum, the distance represents a track of 7130 km (Figure 5) over the course of 18 months. It will be interesting to further explore Hermes’ movements in the context of Atlantic Ocean current patterns and assumed turtle migratory routes (Figure 4). This will help generate hypotheses on the likely route and timing on Hermes’ voyage.

transatlantic route

Figure 5. A theorized trans-Atlantic direct route

This July, Kai Marine scientists and a group of Spanish fishermen, will join US government scientists on a trip to Florida to see hatchling loggerhead turtles emerge from nests on a beach not far from where Hermes was captured. The trip is an effort to thank fishermen for their efforts to reduce sea turtle bycatch in longline fishing gear by switching to deep sets and using mackerel bait. This will also provide an opportunity to link resources, such as sea turtles, between the US East Coast and the Mediterranean, as Hermes has already done.

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