Kids ask: Sea turtles emerge with shell, but fate of hatchlings uncertain
"How do sea turtles get their shells?" asked Emily Bronswick, 9, a fourth-grader W.C. Petty Elementary School in Antioch.
Incredibly slow-moving on land as it struggles to haul its immense body weight across sand, the sea turtle sheds its slow image when its takes the plunge into ocean water. Sea turtles are sleek and adept at swimming and diving in the deep ocean water despite their oversized forms.
There are seven species of sea turtles. The smallest is the Pacific ridley weighing in at 90 pounds. The gigantic leatherback can weigh as much as 1,100 pounds and is the largest of all turtles and tortoises. Marine biologists and zoologists know what kind of food they eat, how they reproduce, how long they can live and how they evolved. But sea turtles haven't let on about their habits as youngsters. No one really knows for sure how sea turtles survive their first few years in the ocean.
Sea turtles are very large reptiles. Like all reptiles, sea turtles hatch from eggs. Inside the egg shell is a baby turtle with a hard shell.
"A turtle's shell is developed in its egg during incubation and is considered part of its skeletal system," said Thad Dirksen of SeaWorld San Diego. "While there are many types of sea turtles, the incubation period for a sea turtle egg is approximately two months. When a turtle hatches, its shell is already part of its body and grows in size as the turtle grows."
The shell is a complex structure. Dirksen said, "The turtle's upper shell is called a carapace, and it is composed of about 50 to 60 bones. The lower shell, called the plastron, has evolved from the turtle's collarbones and the ribs. Joining the carapace and the plastron is a bony structure called the bridge."
One species of sea turtle does not have a hard shell - the leatherback sea turtle. Instead it has a leather covering with seven ridges called keels. Its leather covering and oily skin are insulators that allow leatherbacks to command colder water than other sea turtles.
Female sea turtles may swim for hundreds of miles in the ocean, but when it's time to lay their eggs, they find the beach where they were born. They use their flippers to dig a pit for the eggs, placing as many as 150 eggs in different clutches along the beach.
You might think that all those eggs would mean the world is full of sea turtles, but unfortunately, only about one in 100 hatchlings survives. Predators nab the eggs and hatchlings. As well, development along beaches has limited the space where female sea turtles can lay their eggs.
Humans also have limited the sea turtle population and all species are threatened. The turtles are accidentally caught in fishing nets and die. In some areas of the world they are fished for their meat, shell and flippers.
Scientists fear that global warming might change the gender outcome of hatchlings. When eggs rest in temperatures above 85 degrees, they become female sea turtles. Too many female sea turtles could mean an end to the species altogether.
Governments around the world have enacted treaties to protect this species.
Check these out
The Antioch Public Library suggests these titles on sea turtles:
• "All About Turtles," by Jim Arnosky
• "(Up Close) Reptiles," by Paul Harrison
•"Reptiles," by Melissa Stewart
• "Turtles," by Mervin F Roberts
• "I Wonder Why Snakes Shed Their Skin and Other Questions About Reptiles," by Amanda O'Neill
On the Web:
oaklandzoo.org/animals/reptiles
kids.yahoo.com/animals/reptiles
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