Turtle-cams

A turtle’s underwater life has long been a mystery for science. Modern equipment such as GPS loggers give a lot of interesting insight into the turtle’s life, but there are things that GPS loggers simply cannot register. To learn more about the behaviour of turtles on a fine spatio-temporal scale, scientists resort to different technologies.

In 2005 Dr Richard Reina from Monash University collaborated with National Geographic to study the behaviour of female leatherbacks during their nesting season. The researchers attached video cameras to the carapace of female leatherbacks using suction caps. The cameras were automatically released from the turtle after several hours and the researchers then relocated the devices using a VHF transmitter. The footage presented an interesting view of underwater life from a turtle’s perspective and provided new insight into the private life of leatherbacks:

  • The video showed that the females turtles did not feed during the nesting season (which can span several months!).
  • The footage also exposed the aggressive and harassing behaviour of males wanting to pair with the females. Some males would repeatedly strike and bite the females. Others would even try to prevent the females from returning to the surface.
  • The video also revealed that some females seemed to actively avoid the males.

The results of this study were published in the Journal of Experimental Marine Biology and Ecology.

Using the turtle-borne camera has therefore given the researchers a great perspective on what the turtles do in their natural environment. New research published last month in Frontiers in Ecology and Evolution studied the feeding behaviour of leatherbacks off the coast of Nova Scotia. In the following video you can see a leatherback looking for its favourite meal!

Video courtesy of the Canadian Sea Turtle Network

Long-distance migrations

Most sea turtles come back to nest on the beach where they were born. How they do this, is still a mystery.

In their breeding years turtles will migrate from their feeding grounds to their nesting grounds. Before modern technology was available, scientists could only guess how far or where the turtles would go. Nowadays, GPS tags allow us to study the migrating behaviour of sea turtles.

The most common practice is to tag a nesting female turtle by placing a satellite tag on her shell. Out in the ocean, the GPS calculates the geographic position of the turtle every time she surfaces to breath. This information is relayed to the researcher’s computer via satellite. The turtle can be tracked for as long as the tag works, which can be weeks, months, and sometimes even years.

A green sea turtle returning to the sea with a satellite tag on her carapace (photo couretesy of Nicole Esteban)

A green sea turtle returning to the sea with a satellite tag on her carapace
(photo courtesy of Nicole Esteban)

Thanks to satellite telemetry studies, we now know where nesting turtles have their feeding grounds. For example, we now know that some of the turtles nesting on Ascension Island migrate to their feeding grounds in Brazil. This migration is quite a feat, considering that the trip from Brazil to Ascension Island is over 2000 kilometres and the turtles’ destination is a remote island less than twenty kilometres across.

Science has yet to find out how turtles navigate such vast distances. One hypothesis is that they use Earth’s magnetic field for navigation. In fact, a turtle’s ability to navigate the oceans of the world is one that amazed Charles Darwin himself, as shown in his Letter to Nature in 1873:

“Even if we grant to animals a sense of the points of the compass, of which there is no evidence, how can we account, for instance, for the turtles which formerly congregated in multitudes, only at one season of the year, on the shores of the Isle of Ascension, finding their way to that speck of land in the midst of the great Atlantic Ocean?”

Recently, the longest ever published migration for an adult cheloniid (a hard-shelled marine turtle) was recorded: a green turtle swam almost 4000 kilometres from its breeding grounds in Diego Garcia to its feeding grounds off the coast of Somalia!