![]() One unifying aspect of sea turtle migrations is their ability to return to specific nesting sites over vast areas of ocean year after year. This is thought to be an anti-predator adaptation - there are simply too many eggs for the predators to consume. Both species of ridley sea turtle nest in large aggregations, arribadas. Green sea turtles and hawksbill sea turtles shuttle between fixed foraging and nesting sites. Kemp's ridley sea turtles, loggerheads and flatback sea turtles migrate between breeding areas and a series of coastal foraging areas. Satellite tracking of leatherbacks showed that they tended to stay within relatively food-rich areas of the ocean during their migration. Leatherbacks and olive ridley turtles roam widely and unpredictably before returning to specific breeding sites. Adult sea turtles can be divided into 3 categories according to their movements. Juveniles often reside in coastal feeding grounds, as with green sea turtles and loggerheads. Adult turtles may learn aspects of the magnetic field and use this to navigate in a learned rather than innate way. These responses are inherited rather than learned since the hatchlings tested were captured before reaching the ocean. For example, when exposed to fields characteristic of a region at the edge of the gyre they responded by orienting in a direction which would keep them within the gyre. It has been shown that loggerheads use the magnetic field to stay within the gyre. Hatchling loggerheads mature within the North Atlantic Gyre and it is important that they stay within this current system since here water temperatures are benign. The ability to head in a given direction without reference to landmarks, is called a compass mechanism and where magnetic cues are used to achieve this it is called a 'magnetic compass'. Further offshore the Earth's magnetic field is used to maintain an offshore direction and therefore head towards the open sea. This means they swim offshore, since close to the shore, wave crests run parallel to the beach. Loggerhead and green turtles can detect the orbital movement of waves and use this information to swim perpendicular to the waves crests. Hence, the use of moonlight by turtle hatchings as a navigational cue can be considered an ' evolutionary trap'. This navigational mechanism becomes a handicap if nesting sites are affected by artificial lighting since this can mean that hatchlings head towards the artificial lights rather than offshore towards the moonlit sea. Studies of loggerhead and leatherback hatchlings have shown that moonlight reflected from the sea is an important visual cue in guiding movement from the beach to the sea. The first part of the hatchling migration is called the 'frenzy period' which involves almost continuous swimming for the first 24–36 hours. ![]() Therefore, sea turtle hatchlings move offshore as an innate behaviour. Hatchling migration Įfficient movement of hatchlings away from the beach and shallow coastal waters is important in reducing the length of time that they are vulnerable to predators, which target the hatchlings on the beach or in shallow waters. There is evidence for this ability in juvenile green sea turtles. Some have suggested that juvenile and adult turtles might use the Earth's magnetic field to determine their position. The ability of adult sea turtles to travel to precise targets has led many to wonder about the navigational mechanisms used. Although the foraging movements of leatherbacks seem to be determined to a large part by passive drift with the currents, they are still able to return to specific sites to breed. Instead, they forage in the open sea in complex movements apparently not towards any goal. Others such as the leatherback sea turtle and olive ridley sea turtle do not show fidelity to any specific coastal foraging site. The loggerhead sea turtle uses a series of foraging sites. Some such as the green sea turtle shuttle between nesting sites and coastal foraging areas. Several main patterns of adult migration have been identified. The feeding and nesting sites of adult sea turtles are often distantly separated meaning some must migrate hundreds or even thousands of kilometres. ![]() They then maintain an offshore heading until they reach the open sea. Sea turtle hatchings emerge from underground nests and crawl across the beach towards the sea. Sea turtle migration is the long-distance movements of sea turtles (superfamily Chelonioidea) notably the long-distance movement of adults to their breeding beaches, but also the offshore migration of hatchings. ![]() The green sea turtle migrates between its nesting sites and its coastal foraging areas. ![]()
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