Deft diving turtle tactics

How do turtles survive long trips across the ocean? At the Society for Experimental Biology conference on Friday 12 April Ms Corinne Martin (University of Wales Swansea) will present evidence of energy-saving diving patterns adopted by green turtles to survive long ocean trips.

The turtles breed at Ascension Island, undertaking long-distance migrations greater than 2 300 km between the island and their feeding grounds on the Brazilian coast. During their trip across the ocean they don’t feed, relying on limited fat reserves to keep them going. In order to avoid running out of fuel the turtles appear to have evolved cost-efficient diving behaviour. By attaching diving computers to five female turtles Ms Martin and colleagues were able to show that the turtles descend fast to save energy and then rise passively using buoyant lift generated by lung deflation

Green turtles dive with inflated lungs, and because of lung compression with depth, their buoyancy changes dramatically during the course of a dive. By descending fast near the surface, they minimise the time spent fighting up-thrust and, therefore, minimise the energy cost of descent, until lungs have become sufficiently compressed with depth. Thus turtles optimise their diving behaviour to ensure limited oxygen stores are used in a cost-efficient way, maximising their time at depth.

“Green turtles are remarkable divers,” says Ms Martin. “They are protected by law in many countries because they are an endangered or threatened species. But, because marine turtles spend over 99% of their lifetime underwater, the scientific knowledge of their at-sea biology is crucial for any conservation programme aiming at protecting this species.”