Our trips to sea are not just to see whales and dolphins they are also trips into the open ocean where we seek other pelagic marine life of interest. Often we encounter sea turtles, especially Loggerhead turtles Caretta caretta but very occasionally Leatherback turtles Dermochelys coriacea too. Both these species are pelagic. Once they have hatched and left their nesting beaches they spend the rest of their lives at sea. Only the females will return to land to lay their eggs, often on the very same beachwhere they were hatched. 

A Leatherback turtle surfaces close to a whale watching boat. 

Leatherbacks are the largest turtles, most are between 1-2m long but some grow to 3m and these can weigh up to 960kg. Of the sea turtles they occur inthe coolest waters (to 4.5 °C), they also dive the deepest (a depth of 1200m has been recorded) and swim the fastest (one was recorded swimming at 22mph!). They feed predominantly on jellyfish and lack a bony carapace like the other sea turtles. Little is known about their social and breeding behaviour at sea. Most of the Atlantic population hatch from breeding beaches in Suriname, French Guiana, Trinidad and Tobago, the Caribbean and Gabon. The females lay up to 9 clutches per season and are not always faithful to the same beach. Each clutch can comprise 110 eggs. Here in the Azores they are always seen alone (not including their usual entourage of pilot fish) and offshore in deep water.

This year on 6thJuly, south of Pico we encountered one Leatherback turtle that behaved very strangely. It repeatedly spun, rolled and inverted itself on the surface, flipper slapping like a Humpback whale. Eventually it dived away as normal but I have no idea what caused this behaviour.

 

Three photos illustrating some strange surface behaviour shown by a Leatherback turtle during a recent encounter. 

Loggerhead turtles are the second largest species of turtle. The largest can measure around 2m long. Most weigh between 80-200kg but the heaviest recorded was 545kg. They prefer warmer waters than the Leatherbacks(13°C– 28°C) but also feed on jellyfish. We sometimes see them feeding on the Portuguese man-o-war Physalia physalis. Most of the Atlantic population hatch from nesting beaches located between Virginia on the east coast of North America to Brazil in South America.  Some, however, also come from the Cape Verde islands in the east Atlantic. Females lay on average 4 clutches of eggs per season.

 

The distinctive prefrontal scales on the head of this turtle help to identify it as a Loggerhead turtle. 

Once at sea the Loggerhead turtles drift around the Sargasso sea current and can be encountered around the Azores at any time of year. We see both young and old Loggerheads,sometimes close to land, even during shore dives. They typically range in size from around 25cm to nearly 100cm long. Interestingly the carapace of the young turtles have distinctive serrations (perhaps to protect them from predation).

 

Portuguese man-o-war are a favourite food.

The serrations on the back of this young Loggerhead turtle may deter predators.