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Marine Life of Midway Atoll

Hawaiian Green Turtle / Chelonia mydas

	Description Adult carapace (shell) can be 3-4 ft in length and vary in color from black to greenish or brown. Bold streaks and/or spots, algal growth common. Small, round head. Long prehensile tail in sexually mature males. May weigh up to 400 lbs (178 kilos). Common name comes from the color of their body fat.
Hawaiian green turtle Photo credit: Robert Shallenberger

Distribution

Found throughout the Hawaiian archipelago. Though subadults and adults are common, the number of green turtles living and foraging within Midway's lagoon is undetermined at this time. Many of Midway's turtles have been tagged, providing a useful tool for monitoring the population.

Feeding

Juveniles, sub-adults and adults forage on sea grasses and macro algae "pastures". Foraging grounds restricted to depths where sunlight, substrate and nutrients are conducive to plant growth, usually 3-10 meters in depth. Forage on macro algae species in the Northwestern Hawaiian Islands include Caulerpa, Turbinaria, Spyridia, Codium, and Ulva.

Breeding

Adults migrate from foraging grounds throughout the Hawaiian Islands to breeding grounds. Males appear to migrate every year, arriving ahead of the females. Females only migrate every 2- 4 or more years. Copulation occurs in shallow waters near nesting beaches.

The first successful nest ever recorded at Midway Atoll was in 2006 on Spit Island and the second nest hatched on Sand Island in September 2007, encouraging hopes that Midway will become a sea turtle refuge for nesting.

Ninety percent of all Hawaiian green turtles breed and nest at French Frigate Shoals (FFS), a cluster of sand islets located at the approximate midpoint of the Hawaiian Archipelago. Nesting at FFS occurs from late April through September with a peak in June-July. Each female deposits 1-5 egg clutches (average 1-2) at 11-18 day intervals.

Hatchlings emerge en-masse, usually at night, from a sandy 2-ft deep nest after about 60 days. Hatchlings move down the beach and into the ocean. They become sexually mature between 10-60 years of age, (average age= 25 years).

Mortality

Tiger sharks are primary predator. Entanglement in marine debris and nets, as well as the ingestion of plastics, are a serious problem.

Conservation

Disturbing turtles basking on the beach may result in them avoiding those beaches as they do not feel "safe". As they mature, sea turtles will not nest at beaches where they have been disturbed in the past. Rules at Midway require all to stay at least 100 feet away from any basking sea turtle.