Green Sea Turtles

What do green sea turtles and cows have in common? Food.

Adult green sea turtles are completely herbivorous (the only sea turtles who are). That's probably why this species is sometimes called the "cows of the ocean"—not to be confused with manatees and dugongs, whom some people have dubbed "sea cows." Hatchling and young adult green sea turtles eat an omnivorous diet of worms, aquatic insects, and ocean plant life. Once these turtles reach 8 to 10 inches in length, however, they switch to an herbivorous diet and stick with it for the rest of their lives.

A green sea turtle's finely serrated jaws are well-equipped to tear vegetation such as sea grasses and algae, which they digest with the aid of special bacteria in their intestines. The turtle is named for its green body fat, which is visible underneath the shell—or carapace—on its back. The high algae content of their diet is believed to be responsible for the color of their body fat. A green sea turtle's carapace can range in color from dark green to brilliant brown yellow, gray, or black.

The green sea turtle is the largest of the Cheloniidae family, which includes all sea turtle species except the leatherback, a member of the family Dermochelys. Green sea turtles, on average, measure 36 to 40 inches in length and weigh 300 pounds. However, green sea turtles weighing over 500 pounds are not uncommon. The largest specimen ever found was 5 feet long and weighed 871 pounds. Adult male and female green sea turtles exhibit sexual dimorphism, meaning the two genders have physical characteristics that make them easily distinguishable. Males have long, thick tails, while females have short, thinner ones.

Green sea turtles are distinctive from other sea turtle species in several ways. For instance, they are the fastest, with the ability to travel up to 300 miles in 10 days. They also look different: they have a flatter oval body. And unlike other sea turtle species, which all have two pairs of scales in front of their eyes, green sea turtles make do with just a single pair.

Atlantic vs. Eastern Pacific

Although they are rarely seen in the open ocean, green sea turtles are highly migratory. Some feed off the coast of Brazil and nest nearly 1,400 miles away on Ascension Island. The species is found in all temperate and tropical waters around the world. However, there are two sub-species that are found in different geographic locations: The Atlantic green sea turtle (Chelonia mydas) is found in the Atlantic Ocean, and Eastern Pacific green turtle (Chelonia mydas agassizii) is found in the eastern Pacific Ocean.

Atlantic green sea turtles roam as far south as Argentina and South Africa. They are commonly seen around Cape Verde and the Cayman Islands. Up until the 18th century, they could be found in the millions from North Carolina to Argentina. The Eastern Pacific green sea turtle is sometimes called the black sea turtle because of its black carapace. This subspecies has been seen from Alaska to the coast of Chile, and hibernates in the northern Gulf of California. The color of its shell is not the only thing to differentiate the Eastern Pacific from other green sea turtles: The carapace is elevated and has steeper sides, and the head is smaller.

Green sea turtles prefer habitat near the coastline around islands and protected shores. They feed on the abundant submerged vegetation found in crevices in shallow waters. Since their diet consists mainly of plants low in vitamin D, green sea turtles occasionally bask on quiet beaches, soaking up the sun's natural vitamin D. Basking is also thought to be a way for green sea turtles to avoid predation by sharks and to boost their body temperature and metabolism. The green sea turtle diet is also low in protein, which is thought to account for the species' relatively late reproductive maturity (at 20 to 30 years of age).

Nesting

Green sea turtles nest between the months of June and September, depending on geographic location. Nesting sites are found in the U.S. Virgin Islands, Puerto Rico, and the east coast of Florida. The most significant Atlantic green sea turtle nesting site is Tortuguero, Costa Rica; the primary nesting site for the Pacific green turtle is at French Frigate Shoals, Hawaii. Green sea turtles nest every two to three years. They spend the years between nesting seasons preparing for their long trip from foraging to nesting grounds, which may be more than 1,000 miles apart.

Nesting occurs 3 to 5 times per season at approximately 12-day intervals. Each green sea turtle nest, on average, contains 115 eggs, which incubate for 45 to 60 days before the hatchlings emerge. The sand temperature during incubation will determine the sex of the hatchlings: A low temperature means a male, and high temperature means a female.

Sea Turtle Threats

A serious threat to green sea turtle populations is Fibropapilloma, a contagious, fatal illness affecting green turtles worldwide, but particularly those off the coast of Florida and Hawaii. Fibropapilloma causes bulbous tumors to grow on the soft tissue of the body and on vital internal organs; these tumors spread until they eventually cover the turtle's entire body, and the animal dies.

The cause of Fibropapilloma is unknown, although researchers suspect marine pollution, a virus, or parasites. Green sea turtles in Hawaii have suffered from Fibropapilloma since the1980s, but its prevalence has greatly increased in recent years. In some areas, such as Florida's Indian River, nearly 50% of the green turtle population has been infected with Fibropapilloma.

Once the most abundant of the sea turtle species, the green sea turtle is in serious decline. The turtle has a history of exploitation by humans for its flesh, fat, and eggs. Turtle soup is made out of the species' body fat. These turtles were used extensively for subsistence purposes by the pre-Columbian cultures of the Caribbean. When Columbus arrived, green sea turtles were abundant, and Europeans who settled throughout the Caribbean quickly took them as a source of protein. Soon, settlers began trading in sea turtles and products derived from them, creating a huge market for the creatures.

Despite the mass harvesting, Caribbean mariners once noted that green sea turtles were so numerous in fishing waters that, at times, it was impossible to maneuver nets or even navigate boats. By the 1800s, however, many sea turtle populations had been devastated. These populations have not recovered to this day.

Unfortunately, green turtle harvesting has increased in recent years due to the profitability of sea turtle products, particularly meat. They are stuffed and used as wall décor, and their carapace is manufactured into trinkets and jewelry.

One of the most important green sea turtle habitats, Hawaii, is still a major trouble spot for the species. During the early 1970s, mass harvesting of green sea turtles occurred annually in Hawaii for profit and for personal consumption.

In 1974, Hawaii passed legislation to protect sea turtles; however, the law was not strictly enforced, and sea turtle populations continued to plummet. Hawaiian sea turtles didn't gain meaningful protection until 1978, when a listing under the U.S. Endangered Species Act made it illegal to hunt, injure, harass, or capture sea turtles without a license. Unfortunately, Hawaii's populations face the threats of destructive fishing techniques, loss of habitat, and Fibropapilloma.

It is estimated that there are less than 200,000 green turtle nesting females worldwide. The species is listed on Appendix I of the Convention on International Trade in Endangered Species, which prohibits all legal trade in green sea turtles, their eggs or any products derived from them. The species is also listed as endangered under the U.S. Endangered Species Act.