Leatherback Turtles: Hatchlings the Roam the Shores

Sea turtles instinctively use the moon and natural light as a guide to the water when they hatch. They can tell the difference between the darker shore and the brighter skies above the water, even as the hatchlings can not see the water.

Hatchlings usually emerge from their eggs in a large group and crawl toward the lowest and brightest horizon, which happens to be water.

However, not all sea turtle hatchlings can easily make their way to the beach.

Researchers recently looked into why baby leatherback sea turtles become disoriented, sometimes circling the sands when trying to find the sea.

Samantha Trail, a Ph.D. student at Florida Atlantic University and the lead author of the study, explained that the goal of their research was to better understand the visual capabilities of leatherback sea turtles in comparison to other species, and animal behavior is a factor.

Leatherback turtles are the furthest apart of all the extant sea turtle species.

Trail believed that those capabilities could differ significantly from those of others.

Trail went on to say that sea finding is a critically essential and conserved behavior with conservation implications, so understanding how it is affected by different conditions or sensory thresholds is an important part of their research.

Which Path to Choose?

Most sea turtle hatchlings follow a straight path from their nests to the shoreline, according to the researchers.

Leatherback (Dermochelys coriacea) hatchlings, on the other hand, frequently wander in circles.

Leatherbacks have been observed to exhibit orientation circles, or tight crawls in a complete circle, more frequently than other species in previous observations, though the reason for this is unknown.

The scientist explained that for turtles, circling wastes energy as it takes longer for them to enter the ocean.

Circling also puts them at an increased risk of danger from predators like crabs and birds.

To figure out why some hatchlings circle, and why this behavior is so common in leatherback turtles, the researchers had to first figure out how photosensitive the turtle hatchlings were.

Their research revealed that leatherbacks were found to be 10 to 100 times less sensitive to light wavelengths than as compared to loggerhead hatchlings.

They also discovered that there were no structural differences that could help with vision in low-light situations.

According to the team, there were no larger corneas or lenses to help gather light.

These findings raised the possibility that circling behavior was related to the amount of light on the beach during the hatchlings' journey from the nest to the sea.

The team then compared how the two species acted in the bright light of a full moon compared to when only starlight during a new moon is the source of light.

According to Trail's research, circling is associated with new moon conditions, when light levels are low.

Although still below, these light levels are much nearer to the visual perception tolerances of leatherbacks than other species.

Discrimination thresholds, on the other hand, imply that leatherbacks might be unable to distinguish the shore from the landward direction at least at some wavelengths, according to Trail.

New Moons and Longer Trips

Although leatherback hatchlings often have trouble determining the horizon over the sea, they eventually get there, even if they had to crawl and stop during the low light of a new moon, Treehugger reported.

Trail explained that it takes leatherback hatchlings longer because they stop occasionally to circle, which suggested that they re-evaluate, and eventually confirmed the correct crawl direction.

The team believes that other visual differences aid the turtles in locating mates, prey, or habitats in the open ocean.

These are significant findings, according to Trail, because of the implications for conservation efforts. Artificial lighting may make leatherbacks more susceptible to disorientation.

The different visual capacities of sea turtles that share the same nesting beaches can also be considered an area of interest, according to the scientist.