structural:summarization
Navigation

Below the surface, the sensory cues available for navigation change dramatically. Light availability decreases quickly with depth, and is refracted by the movement of water when present, celestial cues are often obscured, and ocean currents cause continuous drift. Most sea turtle species migrate over significant distances to nesting or foraging grounds, some even crossing entire ocean basins. Passive drifting within major current systems, such as those in the North Atlantic Gyre, can result in ejection well outside of the temperature tolerance range of a given species, causing heat stress, hypothermia, or death. In order to reliably navigate within strong gyre currents in the open ocean, migrating sea turtles possess both a bicoordinate magnetic map and magnetic compass sense, using a form of navigation termed Magnetoreception. Specific migratory routes have been shown to vary between individuals, making the possession of both a magnetic map and compass sense advantageous for sea turtles.

A bicoordinate magnetic map gives sea turtles the ability to determine their position relative to a goal with both latitudinal and longitudinal information, and requires the detection and interpretation of more than one magnetic parameter going in opposite directions to generate, such as Magnetic field intensity and Inclination angle. A magnetic compass sense allows sea turtles to determine and maintain a specific magnetic heading or orientation. These magnetic senses are thought to be inherited, as hatchling sea turtles swim in directions that would keep them on course when exposed to the magnetic field signatures of various locations along their species' migratory routes.

Natal homing behavior is well described in sea turtles, and genetic testing of turtle populations at different nesting sites has shown that magnetic field is a more reliable indicator of genetic similarity than physical distance between sites. Additionally, nesting sites have been recorded to "drift" along with isoline shifts in the magnetic field. Magnetoreception is thought to be the primary navigation tool used by nesting sea turtles in returning to natal beaches. There are three major theories explaining natal site learning: inherited magnetic information, socially facilitated migration, and geomagnetic imprinting. Some support has been found for geomagnetic imprinting, including successful experiments transplanting populations of sea turtles by relocating them prior to hatching, but the exact mechanism is still not known.