Hawaiian Green Turtles (Chelonia mydas)

This is a portrait of Zeus, the largest Hawaiian green turtle that we see regularly at the Turtle House.

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The following material is reproduced verbatim from:

Hawaiian Sea Turtles

A pamphlet published and distributed by U.S. National Marine Fisheries Service in cooperation with Center for Marine Conservation, Mauna Lani Resort, Inc. and the U. H. Sea Grant Extension Service (August 1991)

Permission for use graciously granted by the U.S. National Marine Fisheries Service.

Biology of a Sea Turtle

Sea turtles are graceful saltwater reptiles, well adapted to life in their marine world. With streamlined bodies and flipper-like limbs, they are able to swim long distances in a relatively short time.

When they are active, sea turtles must swim to the ocean surface to breathe every few minutes. When they are resting, they can remain underwater for as long as 2 1/2 hours without breathing. Green turtles often rest in caves or under ledges in deep water.

Although sea turtles live most of their lives in the ocean, adult females must return to land in order to lay their eggs. Scientists believe that nesting female turtles return to the same beach on which they were born. Often, sea turtles must travel long distances from their feeding grounds to their nesting beaches. Just how sea turtles find their nesting beaches is unknown.

Some are Long-Distance Travelers

Hawaii's green turtles migrate up to 800 miles from their feeding areas near the coast of the main islands to nesting beaches in the Northwestern Hawaiian Islands. The males accompany the females in this migration and mate with them offshore from the nesting beaches.

Females often come ashore to nest several times in a season, but wait two or three years before nesting again. Green turtles nest only at night and can be frightened away by lights or movement. It is not easy for these turtles to find a suitable nesting site on land, where they no longer have the buoyancy of water to support their heavy bodies. While on land, these animals shed large, sticky tears which remove excess salt from the body and prevent the eyes from being covered with sand.

When a female finds a suitable nesting site, she uses her flippers to dig a body pit about her. She then digs a flask-shaped egg cavity with her rear flippers. This arduous nesting effort generally lasts all night. After depositing about 100 eggs, the female covers the nest with sand and returns to the sea, leaving the eggs to incubate during the next two months.

After hatching, the tiny, one-ounce turtles take several days to emerge from their nest. A single hatchling would not be able to emerge from the nest by itself. Working as a team, hatchlings scrape sand off the roof of the nest cavity and pack this sand on the floor. In doing so, the hatchlings raise their nest toward the surface of the beach. When they are about an inch from the surface, the topmost hatchlings cease their activities if the sand is hot. Cool sand indicates that it is night or an overcast day: the hatchlings then emerge from the nest, thereby avoiding the sun's heat and perhaps predatory birds.

Once out of the nest, the hatchlings race to the water and swim constantly for the next 36 to 48 hours. They are then probably carried by currents to favourable areas in the open ocean, where they grow for several years until they join adult and juvenile turtles at the coastal feeding grounds. While in the open ocean, young green turtles are probably carnivorous and feed on invertebrates such as jellyfish.

Only a Few Hatchlings Per Nest Will Survive To Adulthood

Some hatchlings never reach the ocean and are snatched up by hungry crabs. Hatchlings may also be disoriented or impeded by obstacles and die from the sun's heat. Once in the ocean, sharks and possibly other carnivorous fish eat hatchlings.

Due to their size and swiftness in the water, adult sea turtles have only two predators: sharks and people. Tiger sharks regularly feed on all sizes of green turtles.

Hawaiian Green Turtles Are Slow Growers

The life span of sea turtles is unknown. Hawaiian green turtles seem to grow very slowly in the wild and may take 10 to 50 years (average 25 years) to reach sexual maturity.

Male and female green turtles look alike until they are mature. Then, the male develops a long tail extending beyond the hind flippers. A female's tail extends only a short distance beyond the end of her shell.

Generally, only female sea turtles leave the ocean after entering it as hatchlings. But in the Northwestern Hawaiian islands male and female green turtles crawl onto beaches and lie motionless in the sunlight for hours. Turtles may bask in order to increase their body temperatures or to avoid tiger sharks.

Sea Turtles Facing Extinction?

Six of the seven species of sea turtles are listed as endangered or threatened under the federal Endangered Species Act. An endangered species is in immediate danger of extinction; a threatened species is one that is likely to become endangered in the near future.

Once there were tens of millions of green sea turtles around the world. Now there may be fewer than 200,000 mature females. In Hawaii, the green turtle is a threatened species. Only 100 to 350 females nest each year, principally at French Frigate Shoals in the Northwestern Hawaiian Islands.

To help restore Hawaii's sea turtles to their former abundance, the National Marine Fisheries Service, the U.S. Fish and Wildlife Service, and the State of Hawaii's Department of Land & Natural Resources have formed a Recovery Team. This team will identify research, management, and enforcement needs and will promote conservation through public education programs.

Protection

All sea turtles in Hawaii are fully protected under state law and under the federal Endangered Species Act. These laws prohibit harassing, harming, killing, or keeping sea turtles in captivity without a permit allowing these activities for research or educational purposes. Divers should be aware that riding turtles is illegal and puts these animals under stress.

When returning from foreign countries, U.S. citizens may not enter the United States with any sea turtle products. Violators may receive penalties of up to one year in prison and a $20,000 fine.