NOAA scientists have studied the coastal habitats and nesting beaches of sea turtles for decades. Concern for loggerheads — which are threatened around the world — has spawned hundreds of conservation groups and volunteer networks that watch over nesting areas and help baby turtles make their way to the oceans. But until now, little has been known about their oceanic habitats and long-distance migratory pathways once they get there.
Turtle biologists and oceanographers at NOAA Fisheries' Honolulu Laboratory are just discovering what the turtles have known for millions of years about their movements and habitats once they leave the shore. These scientists have recently uncovered a trans-Pacific "highway" traveled by juvenile loggerhead turtles as they migrate from the nesting beaches of Japan to Baja, Mexico. This information is critical to helping NOAA understanding the habitat of turtles in the open oceans as we find new ways to avoid incidental catches of sea turtles in fishing gear.
In 1997, biologists George Balazs and Denise Parker from NOAA's Honolulu Laboratory initiated a program to begin satellite tracking of turtles that were caught and released from commercial longline vessels. Observers on the commercial longline vessels attached satellite transmitters to turtles that were caught and released alive.
At the same time, another group of Honolulu Laboratory scientists — Jeffrey Polovina, Michael Seki, Evan Howell, and Donald Kobayashi — were developing approaches to use physical and biological data from various NASA and NOAA satellites and oceanographic surveys from the NOAA ship Townsend Cromwell, to study the longline fishing grounds in the central North Pacific.
Polovina and Balazs combined the data from the two studies and learned that in the open ocean, physical features such as zones of surface convergences (boundaries between different water masses) create turtle habitat and foraging opportunities that are as productive as the more familiar coastal habitats like sea grasses and wetlands.
Using a device that measures surface chlorophyll from space, NOAA scientists were able to compare monthly composites of surface chlorophyll with daily positions of the juvenile loggerheads estimated from the satellite. They observed that the turtles were moving westward along the boundary separating the high surface chlorophyll in the north from the low surface chlorophyll waters in the south. The boundary between the northern and southern areas is called the "Transition Zone Chlorophyll Front" (TZCF).
We see in June that the TZCF has moved north and the turtle is again moving westward along it. Finally, in July the chlorophyll front has moved rapidly north to about 40°N latitude and the turtle travels directly north with this shift.
From the tracks of all 26 loggerheads, it was clear that in all seasons there were some turtles moving along the TZCF.
Without the TZCF, it would be difficult for sea turtles to forage in the open ocean. From examining stomachs of loggerheads that have died in fishing gear, scientists know they feed primarily on floating prey, various gelatinous organisms and animals that grow on floating objects, especially gooseneck barnacles. The high chlorophyll on the north side of the TZCF consists of cool water pushed south by the westerly winds, while the low chlorophyll water on the south of the TZCF is warm water pushed north by the trade winds. Therefore, the TZCF marks a zone of surface convergence where the cool and denser water on the northern side sinks beneath the warm and lighter water on the southern side. This surface convergence concentrates floating prey for the loggerhead turtles.
While oceanographers have long known of the presence of these high and low chlorophyll regions, the boundary between the two received little attention until the turtle "fleet" showed that it is an important forage and migratory pathway. Since this finding, scientists have observed that the TZCF also coincides with the fishing ground for juvenile albacore tuna and is a foraging region for albatrosses from Hawaii.
NOAA scientists have used other satellite oceanographic data, including altimetry, to estimate ocean currents. These data, when merged with the loggerhead movements, indicate that the turtles are not just passively drifting with the currents, but seem to know their location in the ocean and have an internal "map" of their foraging and nesting sites.
All six species encounter human impacts in their nesting environment as well as in the marine environment. Impacts to the nesting environments include egg poaching, erosion of nesting beaches, compaction of beaches by heavy machinery and off-road vehicles, and fortification of beach front property, which results in loss of a dry nesting beach. Impacts in the marine environment include habitat destruction from dredging, turtle consumption of marine debris such as plastic and Styrofoam, which interferes with metabolism), and marina and dock development, which causes foraging habitat to be destroyed or damaged.
Biology
Distribution
Threats
Relevant Web Sites
LOGGERHEAD SEA TURTLE TRACKING: Grays' Reef Satellite Tagging Project
Loggerhead Turtles: Gray's Reef National Marine Sanctuary
Research in the Flower Garden Banks
Caribbean Conservation Corporation
Media Contact:
August 13, 2002 — It's 1 a.m. on a dark, warm night in July as the mammoth, 40-year-old sea turtle makes her way down the beach toward the ocean. She has just finished nesting in the sand dunes, laying eggs to ensure the future of her dwindling species. In eight weeks, hundreds of her hatchlings will emerge from the nest and, driven by the instinct for survival, will attempt their own journey toward the open sea. Few will make it to adulthood, becoming victims of predators, the environment and human activity (i.e., coastal development, increased human use of nesting beaches, pollution and shrimp trawling). The mother turtle does not look back; her babies are on their own now.
The figure to the right (Click image for larger view.) shows a turtle traveling westward from March through July 2002. The red circles represent the turtle's daily positions, and the background represents the surface chlorophyll estimates. The TZCF is marked with a black line as the sharp boundary between the high chlorophyll values shown as green and yellow and the low chlorophyll values shown as purple and blue. In March, the turtle is located at the TZCF at about 153°W longitude and 35°N latitude. In April and May, the turtle travels westward along the TZCF, although its positions toward the end of May suggest that the animal is then moving north of the front.
This turtle study is a pioneer in showing the value of combining animal movements and oceanographic data from satellite remote sensing. NOAA Fisheries is now expanding this work to include olive ridley and leatherback sea turtles. These results are being used to provide a basis for management action that restricts longline fishing in specific times, areas and depths to reduce the incidental catches of sea turtles. NOAA scientists have just initiated work as part of NOAA's Ocean Exploration Program to attach electronic tags to tunas, sharks and marlins to describe their dive and migration patterns. The scientists will combine these movement data with satellite oceanographic data to see what can be discovered about their oceanic habitats.
Sea Turtles
Turtles are saltwater reptiles, well-adapted to life in their marine world. Although sea turtles live most of their lives in the ocean, adult females must return to land in order to lay their eggs. Sea turtles often travel long distances from their feeding grounds to their nesting beaches. Six species of turtles (Green, Hawksbill, Kemp's Ridley, Leatherback, Loggerhead and Olive Ridley) are currently listed as endangered or threatened under the Endangered Species Act.
Loggerhead Sea Turtles (Caretta caretta)
Loggerheads are the most abundant species in U.S. coastal waters and have been listed as threatened throughout its range—since July 28, 1978 (43 FR 82808), and its status has not changed.
Adults and sub-adults have a reddish-brown carapace. Scales on the top and sides of the head and top of the flippers are also reddish-brown, but have yellow borders. The neck, shoulders and limb bases are dull brown on top and medium yellow on the sides and bottom. The plastron is also medium yellow. Adult average size is 92 cm straight carapace length; average weight is 115 kg. Hatchlings are dull brown in color. Average size at hatching is 45 mm long; average weight is 20 g. Maturity is reached at between 16-40 years. Mating takes place in late March-early June, and eggs are laid throughout the summer.
Loggerheads are circumglobal, inhabiting continental shelves, bays estuaries, and lagoons in temperate, subtropical and tropical waters. In the Atlantic, the loggerhead turtle's range extends from Newfoundland to as far south as Argentina. During the summer, nesting occurs in the lower latitudes. The primary Atlantic nesting sites are along the east coast of Florida, with additional sites in Georgia, the Carolinas and the Gulf Coast of Florida. In the eastern Pacific, loggerheads are reported as far north as Alaska, and as far south as Chile. Occasional sightings are also reported from the coast of Washington, but most records are of juveniles off the coast of California. Southern Japan is the only known breeding area in the North Pacific.
The most significant threat to Loggerhead populations is coastal development, increased use of
nesting beaches by humans, and pollution. Shrimp trawling has also had a devastating impact on the
populations.
Gordon
Helm or Susan Buchanan, NOAA Fisheries,
(301) 713-2370