How satellite tracking revealed the migratory mysteries of endangered Atlantic loggerhead turtles

In a paper in the journal Current Biology, Dr Brendan Godley and an international team describe how they used satellite tracking systems to follow the journeys of ten turtles from Cape Verde, West Africa, which is one of the world's largest nesting sites for loggerheads and a hotspot for industrial fishing. What they found could turn current conservation strategies upside down, as the team discovered the turtles adopted two distinct approaches to finding food, linked to their size.

Previously it was thought that hatchlings left the coastal region to forage far out at sea before returning, later in life, to find food closer to shore. However the new findings show that the oceanic habitats contained far larger animals than was previously thought. The team tracked the turtles as they left nesting sites, following them for up to two years over ranges that covered more than half a million square kilometres.

Dr Brendan Godley, of the University of Exeter, said: "We were surprised to find such large turtles looking for food out in the open ocean, as it was previously thought that animals of this size would have moved back to forage in coastal zones. This means there are much greater numbers of the breeding population out at sea and far more that are vulnerable to the intensive longline fishing effort that occurs in that region."

He added: "From the information collected, we have been able to determine how much time these animals are spending within the sovereign boundaries of each country in the region. This research highlights how complicated the migration of marine vertebrates really is and how sophisticated our conservation efforts must be to safeguard these animals. Given the range these reptiles can cover an international cooperative effort in seven African states is needed to create a strategy that would protect them."

Research* shows that in 2000 1.4 billion hooks were cast into the world's oceans through industrial fishing. It's thought that globally more than 200,000 loggerhead turtles were incidentally caught by fisherman scouring the waters for other species such as tuna and swordfish. Of these, tens of thousands are thought to die as a result. 37% of this fishing effort was in the Atlantic and a major hotspot for fishing is found off West Africa, the region where the Cape Verdean turtles reside.

In recent years marine turtle researchers have been using satellite telemetry to track turtle migrations. Satellite transmitter tags are attached to the shell of the turtle so that every time the turtle surfaces to breathe, the tag transmits the turtle's position, as well as other information (e.g. depth and duration of dives), to satellites orbiting above, which then relay the data by e-mail to the computer of the scientist who attached the tag. For more information about tracking sea turtles, visit www.seaturtle.org/tracking

Source: University of Exeter