Loggerhead sea turtles (Caretta caretta) are widely distributed in tropical and subtropical waters around the world. The species is considered endangered by the International Union of Nature and Natural resources (IUCN), quoted in the Red Data Book and commence is prohibited in those countries that have signed the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Loggerhead sea turtles are highly migratory, which makes their survival dependent on the conservation of widespread marine habitats (including migratory corridors, coral reefs, feeding grounds and nesting beaches).

A loggerhead sea turtle equipped with a satellite transmitter. The loggerheads can be up to about a meter long and weigh about 80 kg (Photo: With the permission from Dr. Flegra Bentivegna, Stazione Zoologica, Napoli).

On their migratory routes sea turtles are especially vulnerable to commercial fisheries using long lines and drifting nets. This type of fishing often takes place along the front systems of the oceans where big ocean current systems meet. Typically, algae, jellyfish and zooplankton accumulate along the front systems attracting bigger sea animals like fishes and sea turtles. An unknown number of sea turtles are caught as by-catch by the above mentioned type of fishery and their faith are often lethal or they become badly wounded.

The feeding grounds and migratory routes of adult loggerhead sea turtles are well defined. But for young (juvenile) loggerheads research has so far been limited. It is known that, juvenile loggerheads are conducting a pelagic existence far from the coast, but knowledge of this stadium is scarce.

By using the newest satellite transmitters it is possible to enlighten this relatively unknown part of the life cycle of loggerhead sea turtles. The Danish Environmental Research Institute, The Danish Aquarium and Shell are cooperating in a scientific project where the migrations of 11 juvenile loggerhead sea turtles in the Northeast Atlantic are followed by satellites. 10 of the 11 sea turtles will be caught off the Azores; a Portuguese Acapulco in the middle of the Atlantic Ocean at the same latitude as Lisbon. The last sea turtle comes from the Danish Aquarium. It has been living here for more than four years after it stranded at the Danish west coast back in 1999.

The juvenile loggerhead sea turtles around the Azores are known to originate from one of the biggest loggerhead nesting populations, located at the eastern coast of Forida, USA. After reaching the sea, these juvenile loggerheads are believed to be carried around the Northeast Atlantic gyre system for up to ten years, perhaps by drifting passively in association with rafts of sargassum weed. But their actual migration routes and navigational skills are not well documented.

One of the few places in the Northeast Atlantic where American juvenile loggerhead sea turtles are regularly seen is at the Princess Alice Bank off the Azores. Here, they seem to gather in spring and summer time.

Banks and Islands at the Azores

Apparently, juvenile sea turtles forage at Princess Alice Bank before they leave in the autumn to continue along the current system encompassing the Sargasso Sea. What triggers the departure from the bank and the duration of their stay in the area is not known.

Eventually, they will find a suitable foraging ground at some distance from their original nesting beach. Here, they will eat and grow into maturity. At this time they will swim towards their nesting beach and along this route they will mate. The loggerhead life cycle is completed when females return to lay their eggs, sometimes only a few meters or on top of the location where they themselves hatched 15 – 40 years ago. A new generation of loggerhead sea turtles is ready to begin a long journey.

Map showing the Northeast Atlantic sea current system encompassing the Sargasso Sea, including the north going Gulf stream and the south going Canary Stream.

Method

Juvenile sea turtles are frequently caught for scientific purpose from Princess Alice Bank, off the Azores. In cooperation with scientists from the University of the Azores and local fishermen, it is the plan to catch ten juvenile loggerhead sea turtles from this area. Satellite transmitters will be attached to the carapace of the sea turtles and they will be released shortly after capture. By using satellite telemetry it is possible to track the sea turtles for up to 450 days along their migration routes in the Northeast Atlantic gyre system (actual tracking length depends on battery durability of the transmitter). Tissue- or blood samples for mtDNA analysis will be taken from the 10 sea turtles, as well as measurements of carapace length and determination of gender. The turtles will also be tagged with plastic tags for eventual later identification.

Collaboration with the Danish Aquarium

The Danish Aquarium is planning a special exhibition called "An Ocean of Technique", which is expected to open 17 July 2004. Sea turtles have a central role in the exhibition focusing on a loggerhead sea turtle which is currently held in one of the basins of the Aquarium. Due to limited space at the Danish Aquarium, they have decided to release the loggerhead sea turtle. The turtle is named "Lucky" because of its peculiar life story.

In December 1999, "Lucky" stranded at the west coast of Denmark. For unknown reasons, the sea turtle must have lost its orientation, and was swept thousands of kilometres away from its normal geographical distribution range. Several factors indicate that "Lucky" lost its track not far from the Azores. First, when "Lucky" was found at the west coast of Denmark she was about the same size (43 cm) as the juvenile loggerheads leaving the Azores in the autumn. Furthermore, not far from the Azores the sea current system bifurcate into the north going Gulf Stream and the south going Canary Stream. In most cases sea turtles follow the Canary Stream but sometimes things go wrong and a few individuals are carried north by the Gulf Stream. The faith of these individuals is lethal in most cases and the survival of "Lucky" is, as its name says, pure luck.

"Lucky" will be released together with the ten wild loggerheads from this scientific research project proposal, and it will also be equipped with a satellite transmitter. Perhaps, by comparing "Lucky`s" journey by the migration routes of the ten wild juvenile loggerheads, it will tell us whether the behaviour of "Lucky" is somewhat distorted. Hereby it may be possible to give a qualified judgement of the justifiability to release sea turtles that have been kept in captivity.

Intermediary coverage

The Danish television station, TV2, will broadcast the entire progress, starting with 10-15 two-minute programmes during the "TV2 weather forecast", describing the stranding and migration patterns of sea turtles and other marine migratory species in comparison with the global patterns of sea currents.

Furthermore TV2 will cover "Lucky’s" journey from the Danish Aquarium to the Azores, the equipment of the satellite transmitter, as well as the release of "Lucky" and the other ten wild loggerhead sea turtles.

TV2 will hereafter follow up on the incoming satellite data from all 11 sea turtles showing their journeys in the Atlantic Ocean. Finally, it is the plan of TV2 to display the Azores for Danish tourists by portraying the Islands in one or two documentaries.

Project aims

• Improve the knowledge of the migration patterns of juvenile loggerhead sea turtles in- or along front systems in the North Atlantic Gyre system.
• Contribute to efficient management strategies for the conservation of the endangered loggerhead sea turtles in the North Atlantic Ocean. Including, measures to prevent juvenile sea turtles ending up as by-catch in commercial fisheries along the front systems.
• Extrapolate the results to other loggerhead populations and other threatened sea turtle species with similar life cycles, like the green turtle (Chelonia mydas), characterized by long, complex migration patterns along current systems.
• Improve knowledge of the dynamics of sea current systems and their use as "migratory highways" for marine animals.
• Contribute to the discussion of the justifiability of releasing animals that have been kept in captivity.
• Promote basic scientific research to a broader group of people than scientists – through television, web-site information and the exhibition at the Danish Aquarium.

In September 2004, the ten loggerhead sea turtles will be caught at the Azores and together with "Lucky" they will be released with satellite transmitters attached at their carapace. Shortly after, the first incoming results of their positions will be received. It will be possible to follow their migrations on this homepage (www.dmu.dk) and at the homepage of the Danish Aquarium (www.akvarium.dk). It is also possible to follow the sea turtles at the homepage of Shell (www.shell.dk).