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Hawaii - The Big Island to Kure Atoll
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Hawaiian Green Sea Turtles
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Green sea turtles get their name from the green-colored fat tissue in its body.
The green sea turtle's Latin name is Chelonia mydas. In Hawaii, the green sea turtle is known as Honu (pronounced hoe-new).
PHYSICAL DESCRIPTION:
Green sea turtle hatchlings weigh about one ounce and have a carapace (shell) length of 2 inches. Subadults average about 200-350 pounds, with a carapace length of at least 2 1/2 feet long. Adults can grow to 4 feet and weigh up to 400 pounds. The carapace is a mottled dark brown on top and creamy white below. The carapace often will be covered in green algal growth. It is very difficult to distinguish between the sexes, except as mature adults, when males have a longer thicker tail than females. Males will also develop a single mating claw on the trailing edge of their fore flippers.
DISTRIBUTION AND RANGE:
Green sea turtles are found throughout the world’s oceans, with major populations in the United Statues found off Florida’s east and west coasts, in the Caribbean, and off the Pacific coast of Mexico. The Hawaiian population of green turtles appears to be genetically isolated from other populations in the Pacific, as they remain within Hawaiian waters throughout their lives. The main Hawaiian Islands serve as a feeding area for subadult and adult green sea turtles; 90% of this population migrate to the Northwestern Hawaiian Islands for mating and nesting.
FEEDING:
Green sea turtles get their name from the color of their body fat, which is green from the algae or limu that they eat. Adult green sea turtles are primarily herbivorous, feeding on nearshore limu pastures around the main Hawaiian islands. However, as juveniles, green sea turtles are omnivorous, feeding on plankton, jellyfish and fish eggs floating near the surface of the open ocean. This juvenile period is termed the “lost years” and lasts about 3-7 years. From the time that the hatchlings enter the water to the time that the turtles show up in the main Hawaiian Islands, it is unknown exactly where the turtles go and what they’re feeding upon.
REPRODUCTION:
Hawaiian green sea turtles do not reach sexual maturity until they are about 25 years old, sometimes taking up to 50 years! Once sexually mature, adults migrate from the foraging grounds to the nesting grounds, primarily at French Frigate Shoals, located 800 miles northwest of the main islands. Males appear to migrate every year, arriving ahead of the females. Females only migrate every 2-4 years. It is believed that females return to the same birth where they were born. Mating starts in March and occurs in the waters adjacent to the nesting beaches. Nesting occurs from late April through September, with a peak in June and July.
Nesting occurs at night, with each nesting female coming ashore to lay eggs as many as five times, at 11 to 18 day intervals. The female digs a broad pit with its fore flippers and an egg chamber with its rear flippers, and then deposits a clutch of 100 to 120 ping-pong ball sized eggs. The female then gently covers the nest by flinging dirt over it with its flippers. The temperature of the eggs during incubation determines the gender of the hatchings: lower temperatures produce males, while higher temperatures produce females.
Hatching occurs at night, after about 60 days of incubation. Working as a group, hatchlings dig to the surface of the nest. They head to the ocean immediately, attracted to the light reflected off the ocean. Seabirds, crabs and fish are often waiting nearby, ready to grab a hatchling as an easy meal. After reaching the water, the hatchlings disappear and are not seen by humans until they appear as juveniles in the nearshore waters of the main Hawaiian Islands.
LIFESPAN:
It is believed that green sea turtle can live up to 80 years of age. Unfortunately, because humans have hunted sea turtles for so long, we have not yet allowed populations to recover fully to track their natural lifespan.
PREDATORS:
The only natural predators of adult green sea turtles are tiger sharks. Hatchlings may fall prey to fish, crabs, birds, or perhaps cats or dogs. Of course, humans are the main non-natural predator of sea turtles, killing them for their eggs, meat, oil, and shell. Because sea turtles are slow-growing and reproduce at such a high age, many populations were decimated to the point of near-extinction.
OTHER THREATS:
The most significant threat to green sea turtles is entanglement in fishing gear, and death from incidental bycatch in commercial fisheries. Sea turtles can be inadvertently caught and downed in trawl nets pulled by fishing vessels harvesting shrimp. The United States has reduced sea turtles deaths by requiring U.S. shrimp trawlers to use turtle excluder devices (TEDs) to reduce turtle drownings; however, mortalities from foreign shrimp vessels may still be substantial. In addition, thousands of sea turtles become entangled in fishing line, discarded nets and plastics floating in the ocean. Plastics are very detrimental when ingested by sea turtles, as they are block the digestive system and are toxic. Cigarette butts are also extremely harmful, as turtles cannot digest the filters which contain toxic ingredients. Noise, lights and beach obstructions are disruptive to nesting areas and threaten the reproductive cycle of green sea turtles.
Up to 50% of green turtles in the main Hawaiian Islands have a disease called fibropapilloma (FP). FP causes tumors as large as a grapefruit to grow over a turtle’s eyes, mouth, neck or flippers. The tumors are not deadly until they block the sight, breathing, or feeding activities of the turtle. The cause of FP is not known, though it occurs more so in areas highly impacted by human activities. It is perhaps related to pollutants, blood parasites, or habitat change.
STATUS:
Listed as a threatened species and protected in Hawaii under state law, the federal Endangered Species Act, and listed under the Convention on International Trade of Endangered Species (CITES), making it illegal to import or export turtle products. It is illegal to kill, capture, or harass sea turtles.
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