HiguInfo- Home of Sea Turtles

In Wangan, Penghu, mating of green turtles usually occurs between March and April, while females generally nest between May and October, with peak nesting occurring in July and August. The number of nests, or “clutches”, laid by females varies from one to nine, with an average of five nests, containing approximately 110 eggs per nest.

The eggs will be incubated for approximately 50 days before hatching. Like many reptiles, sex determination of sea turtles is dependent on the sand temperature during the third week to the fifth week of incubation. Temperatures higher than the “pivotal temperature” produce female hatchlings, while lower temperatures produce males. At the pivotal temperature, a sex ratio of 1:1 is produced.

Green turtle hatchlings are only 4-5 cm in carapace length. In most cases, all turtle eggs hatch at the same time, and 3 to 7 days after hatching, all hatchlings will slowly scramble their way up to the surface. To avoid predators, they usually emerge from the sand during nightfall or dawn. Their emergence is gauged on a cooling sand temperature. When hatchlings emerge from the sand, they look for the brightest horizon, which should be the seaward horizon, with or without the moon. As they reach the seawater, they will swim offshore for at least 24 hours nonstop, dodging every predator imaginable. They have many predators, thus survival rate is low. It is estimated that less than one in a thousand hatchlings will make it to the adult stage.

Before hatchlings grow to become juveniles of 20-30 cm in length, they live a pelagic life, taking shelter in floating sargassum mats, feeding on planktons. When green turtles reach the juvenile stage, they will return to coastal waters, start their benthic life in an area where seagrass and algae are abundant to feed on, and continue to mature. These areas usually co-occur with coral reefs, thus we may often find them in coral reef areas. Matured adult green turtles are usually more than 90 cm in length.

Studies indicate that green turtles that have reached sexual maturity do not mate nor breed every year. Interval between nesting seasons is from 3 to 5 years. Males and females will migrate from their foraging ground to nesting areas to breed. One female will mate with multiple males, and store the sperm in its body for later fertilization. This is why females nest multiple clutches during a nesting season. Only females will come ashore to lay eggs, usually in the same area where they were born.