Where little sea turtle hatchlings drift in ocean currents determines their migrations and selection of feeding sites as adults, new research shows.
When they breed, adult sea turtles return to the beach where they were born. After breeding, adult sea turtles typically migrate several hundreds to thousands of kilometers to their feeding habitats.
There’s been little information about how turtles choose their feeding sites, though. For example, some turtles migrate to feeding habitats thousands of kilometers away, while other turtles don’t migrate or feed in the open ocean.
The study looks at what habitats the turtles would have experienced as juveniles. Newborn hatchling sea turtles are too small to track with satellite tags. However, when they emerge from their eggs, they head to the ocean and drift with ocean currents to their juvenile development habitats.
The researchers combined all the available satellite tracking data on adult turtles with models of how the world’s seawater moves past nesting sites to study where the hatchling sea turtles drift.
By comparing global patterns in the migrations of all satellite tracked sea turtles with global hatchling drift patterns, they showed that adult sea turtle migrations and foraging habitat selections were based on their past experiences drifting with ocean currents.
“Hatchlings’ swimming abilities are pretty weak, and so they are largely at the mercy of the currents,” says Rebecca Scott, leader of the study in Ecology.
“If they drift to a good site, they seem to imprint on this location, and then later actively go there as an adult—and because they’re bigger and stronger they can swim there directly.
“Conversely, if the hatchlings don’t drift to sites that are suitable for adult feeding, you see that reflected in the behavior of the adults, which either do not migrate or they feed in the open ocean, which is not the normal strategy for most turtle species,” explains Scott, who is based at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany.
Many animal groups undertake great migrations, and the process of learning where to go on these travels can take several forms. For example, some juvenile whales and birds learn migration routes by following their mothers or more experienced group members, while other bird and insect species seem to be born with the information or a map sense that informs them where they should migrate.
However, neither of these strategies works for turtles. Once the adult female has laid her eggs on a beach, her involvement in her offspring’s development ends. When the hatchlings crawl down the beach into the water, they are on their own; there is no experienced turtle to follow, and they go where the ocean takes them.
“Although it is known that ocean currents have a large influence on the dispersion of small planktonic organisms, these findings reveal ocean currents also directly shape some the migrations of some of the largest, most powerful long distance migrants in the animal kingdom,” adds Bob Marsh of the University of Southampton, who was Scott’s supervisor and coauthor of the study.
Smith’s NERC PhD studentship and a postdoc position funded by The Future Ocean Cluster of Excellence supported the work.
《Ontogeny of long distance migration》, Published on Journal 《ESA Ecology》in May 2014.