Sensing the Seasonal Change—Leatherback Sea Turtles Reveal A Sixth Sense

As a migratory species, Leatherback Sea Turtles (Dermochely coriacea) are a rare oddity of nature that spend their lives mostly in travel, between their breeding grounds in open ocean and their tropical places of birth. Travelling back and forth between the tropics and their hunting grounds to the north, the unique species follows the cool waters, as they flow throughout the oceans they inhabit. But that doesn't even begin to unravel their mysterious origins or how they know to traverse the seas.

In a new study published in the upcoming issue of the Journal of Experimental Marine Biology and Ecology, a collaborative team of researchers throughout the UK sought to discover how it is that these rare migratory creatures know how and when to leave their tropical summer homes in search of cooler waters. Taking a look into the distinct physiological anomalies of the rare species of sea turtles, which are unlike other sea turtles in that they do not have a hard outer shell, researchers suggest that they have discovered another sensory organ, which acts as a "third eye" to monitor changes in sunlight. Known as the pineal, or "pink spot", the irregular crown on the top of the species' heads was once thought of as a mere birthmark, however, researchers now believe that the patch allows changing seasonal light to indicate migration time directly in the minds of the specie.

"Our study showed that the skeletal structures underlying the pink spot in juvenile and adult turtles are compatible with the idea of a pineal dosimeter function, that would support recognition of environmental light stimuli" lead researcher John Davenport says.

With a thin underlying layer of the skull residing just beneath the distinct pink markings, researchers believe that the pineal acts as a "skylight", wherein day length and light intensity give phonological cues for leatherback migration. Though the researchers have indicated a complex reasoning behind why the lack of pigment and thin skull region would support a biological clock run by exposure to the sun, the research begun on Dermochely coriacea is far from over. As the only species within its genus, and the most widely distributed sea turtle species on Earth, Dermochely coriacea has long been the topic of conservation efforts worldwide, with supporters in every major government agency. Now that tracking can be better monitored, the researchers hope to reveal even more secrets of the elusively unique reptiles, which will help contribute to their further protection and continued migratory quests.