Eye to the Sky

Leatherback sea turtles migrate vast distances – sometimes thousands of miles – between their cool-water, summer feeding grounds in the north and warmer tropical and subtropical breeding/nesting areas. But how do they know when to begin their journey south to breed?

Research by British biologist John Davenport and his colleagues in 2014 studied the leatherback’s pineal spot (or “pink spot”) on the top of their head (shown above). Underneath this area of skin (which can be pink or white), the bone of the skull is much thinner. So, light is able to pass through the skin and bone directly to the brain’s pineal gland which can detect changes in long wavelengths of light. Furthermore, by analyzing a database of endangered Atlantic leatherback sightings around Great Britian, the researchers discovered that they began their migrations south around the late summer equilux – the day when sunrise and sunset are exactly twelve hours apart. Davenport and his colleagues found that day length is a more reliable indicator of seasonal change than changes in water temperature or intensity of light.

More recent research provides insights into the migratory routes that Atlantic leatherbacks follow as they head south to their breeding and nesting habitats and what they eat during their journey. Over a five-year period, scientists from NOAA Fisheries and their partners placed satellite tags on 52 Atlantic leatherbacks and studied their movements. They discovered many of the tagged turtles feeding near southern New England in late summer and early fall which coincided with an abundance of jellyfish (a favorite prey). Additionally, they found some of the tagged leatherbacks foraging offshore of New Jersey during high concentrations of sea nettles (another favorite food). This important research identifies the critical feeding grounds that these endangered Atlantic leatherback sea turtles use as they migrate along the east coast of the U.S. so these areas can be protected. In the future, the researchers hope to learn more about how and why leatherbacks choose their foraging areas and what is the impact of the threats they face as they travel along the Atlantic migration corridor.

Sources:

• ScienceDirect: “Pink Spot, White Spot: The Pineal Skylight of the Leatherback Turtle (Dermochelys coriacea Vandelli 1761) Skull and its Possible Role in the Phenology of Feeding Migrations” by John Davenport, T. Todd Jones, Thierry M. Work, and George H. Balazs (December 2014)
• Smithsonian Magazine: “Why the Leatherback Turtle Has a Skylight in its Head” (January 2015)
• NOAA Fisheries: “Where the Leatherbacks Roam” (March 2024)