Scientists have been using tracking sensors to follow the long treks of individual leatherbacks, then overlaying their routes with sea state data, including near-real time maps of ocean currents gathered by satellites including ESA's ERS-2 and now Envisat.
These giant reptiles - known to reach 2.1 metres in length and weigh in at 365 kg - briefly come ashore to lay their eggs on beaches across French Guiana and neighbouring Suriname, the turtles' last remaining major nesting sites in the Atlantic Ocean. Around nine weeks later the hatchlings emerge en masse and head into the sea, one day to return when they reach maturity and lay eggs themselves.
However each turtle's return is by no means certain. While in open water the turtles have been known to dive as deep as 1,230 metres in search of food, most of the time they do not venture deeper than 250 metres down, leaving them vulnerable to the hooks of longline fishermen – hundreds of thousands of such hooks are deployed daily across the Atlantic.
A paper was recently published in Nature summarising the work done so far in tracking leatherbacks through the Atlantic, submitted by a team of researchers from France's National Centre for Scientific Research in Strasbourg, neighbouring Louis Pasteur University, the French Guiana Regional Department of the Environment and the company Collecte Localisation Satellites (CLS) in Ramonville, specialising in satellite-based systems for location-finding, data collection and Earth Observation.
Pacific leatherbacks follow narrow migration corridors. Researchers hoped that if their Atlantic counterparts acted in the same way then fishing could be restricted across these zones.
Starting in 1999 individual turtles were tracked using the CLS-run Argos system, based on radio-emitting tags whose position can be tracked worldwide to a maximum accuracy of 150 metres. Six American NOAA spacecraft currently carry Argos receivers, with ESA's MetOp series due to join the system following their initial satellite launch next year.
The turtles' tracks were then overlaid with maps of sea level anomalies obtained by merging data with the radar altimeter aboard ESA's ERS-2 with another aboard the NASA-CNES satellite TOPEX-Poseidon.
ERS-2, like its successor Envisat, is part of the select group of satellites equipped with a Radar Altimeter (RA) instrument. By firing thousands of radar pulses off the surface of the sea every second extremely precise ocean height measurement is made possible. Height anomalies detected by this type of sensor are often indicators of the presence of ocean currents and eddies: warm currents can stand up to a metre above colder waters.
By merging multiple radar altimeter results together, the result is a more frequent and higher resolution measurement of sea level anomalies than any one spacecraft could achieve. For example, now that ERS-2's global mission is over, results from Envisat's RA-2 instrument are being combined with similar data from the joint French-US Jason spacecraft and the US Navy's GFO.
Unlike their Pacific relations, the Atlantic leatherbacks do not follow narrow migration corridors but disperse widely - to begin with, the leatherbacks carry out long nearly straight migrations either to the north or to the Equator, swimming across currents as they encounter them. One made it to within 500 km of West Africa before turning back, another came close to Nova Scotia.
Full story can be found
here.
Related stories:
Coral reefs found growing in cold, deep ocean
Imagine descending in a submarine to the ice-cold, ink-black depths of the ocean, 800 metres under the surface of the Atlantic. Here the tops of the hills are covered in large coral reefs. NIOZ-researcher Furu Mienis studied the formation of these unknown cold-water relatives of the better-known tropical corals.
Flying Underwater, Staying Dry
Rutgers physical oceanographer Scott Glenn and his students are flying a submersible robot glider, the Scarlet Knight, across the Atlantic – very slowly, underwater, and without getting wet.
Research around the North Pole
The German research vessel Polarstern has returned today to Bremerhaven from the Arctic Sea. It has cruised as the first research vessel ever both the Northeast and the Northwest Passages and thereby circled the North Pole. The third part of the research vessel's 23rd Arctic expedition, operated by the Alfred Wegener Institute in the Helmholtz Association, started its journey on August 12th in Reykjavik and ended it on October 17th in Bremerhaven.
Climate: New spin on ocean's role
New studies of the Southern Ocean are revealing previously unknown features of giant spinning eddies that have a profound influence on marine life and on the world's climate.
Signals from the Atlantic salmon highway
For years scientists have struggled to understand the decline and slow recovery of Atlantic salmon, a once abundant and highly prized game and food fish native to New England rivers. Biologists agree that poor marine survival is affecting salmon in the U.S. and Canada, but specific causes are difficult to determine in the ocean. Small acoustic tags and associated technology may provide some answers.
Successful series of measurements in Arctic sea ice
The German Research Vessel Polarstern had to prove its ice breaking capabilities in Arctic waters to gain data on two series of long-term research measurements. After working in regions up to latitude 82° N, Polarstern of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association will enter port in Reykjavik (Iceland) on August 10th.
Isthmus of Panama formed as result of plate tectonics
Contrary to previous evidence, a new University of Florida study shows the Isthmus of Panama was most likely formed by a Central American Peninsula colliding slowly with the South American continent through tectonic plate movement over millions of years.
Penguins setting off sirens over health of world's oceans
Like the proverbial canary in the coal mine, penguins are sounding the alarm for potentially catastrophic changes in the world's oceans, and the culprit isn't only climate change, says a University of Washington conservation biologist.
