Ask Dr. Universe: Two questions about sea turtles

  • Sat Feb 8th, 2020 1:30am
  • Life

Dear Dr. Universe: Why won’t a female sea turtle lay her eggs in the ocean? How do baby turtles know where the ocean is when they hatch from their eggs? — Jasmine and Shereen, 8, Gainesville, Florida

Dear Jasmine and Shereen,

Sea turtles spend almost their entire lives in the ocean. Even as babies, sea turtles’ bodies have special traits for living at sea, helping them glide and paddle through the water. After emerging from their eggs, baby sea turtles (called “hatchlings”) scramble to the ocean to live the rest of their lives. Only female sea turtles return to land as adults, to lay eggs and begin the cycle again.

I talked with my friend Frank Paladino to learn more about sea turtles. He completed his Ph.D. at Washington State University. Today he is a professor at Purdue University-Fort Wayne and former president of the International Sea Turtle Society. He is especially interested in leatherbacks, the largest living turtle.

I learned that a female sea turtle must return to the beach to lay eggs, even though she is most comfortable in the ocean. This is because her eggs can only survive on land.

Baby sea turtles breathe through their eggs before hatching. Oxygen passes through the eggshell and membrane, a thin barrier surrounding the turtle. Even buried in sand, the turtle can still breathe through the egg. But they cannot breathe if the egg is in the water.

Sea turtle eggs also need warm temperatures to grow properly. Beaches provide the right conditions to help eggs develop. Mother sea turtles bury their group of eggs (called a “clutch”) in sandy nests to protect them until they are ready to hatch.

But when lots of humans are around, a beach can be a difficult place to lay eggs. “Normally, female turtles do not lay their eggs in the water. But if disturbed when on the beach and distracted multiple nights from returning to the nest, they will dump their clutch in the ocean,” Paladino said.

Humans can also cause problems for hatchlings as they leave the nest and head toward the ocean.

To find the ocean, hatchlings follow the brightest light source. Have you ever noticed how a pond or lake sparkles in the sun? This is because light bounces off the surface of the water. Under natural conditions, the ocean is brighter than the beach because it reflects light from the sun and the moon.

But when humans are around, other light sources can confuse turtle hatchlings. “Lights from houses and hotels on turtle beaches distract them. Instead of going to the sea, they will head toward the house lights which are the brightest horizon,” Paladino said.

Light pollution can be dangerous for hatchlings, so some places have created rules to protect them. Paladino told me that turtle nesting beaches in Florida have shields to block human sources of light. There are even special street lights designed not to confuse hatchlings looking for the ocean.

Sea turtles follow their instincts, in a cycle that takes them from the land to the ocean. Although humans pose challenges to sea turtles, science can help them live alongside each other.

Sincerely,

Dr. Universe

“Ask Dr. Universe” is a science education project based out of Washington State University. Send questions to Dr.Universe@wsu.edu.