Kategorie: News
New Study Shows Remarkable Site Fidelity
Green sea turtles are considered long-distance travelers of the oceans - guided by the Earth’s magnetic field, ocean currents, and the sun, they typically traverse vast stretches of the oceans and return to their birthplace only every few years to reproduce. Researchers were all the more surprised when they discovered a population on the Galápagos Islands that shows remarkably little interest in long-distance travel.
The Galápagos Islands are the only known place in the world where two genetically distinct color forms of the green sea turtle coexist: the “yellow” form, which is actually native to the western Pacific, and the “black” form from the eastern Pacific. Once fully grown, both feed primarily on a vegetarian diet of seagrass and algae and share the same feeding grounds around the islands.
Nine turtles, 418 days, hardly any movement
In 2015, a team led by John W. Rowe (Alma College, USA) and Juan Pablo Muñoz Pérez (Universidad San Francisco de Quito) fitted seven adult males and two females of the yellow form with satellite transmitters and tracked their movements for up to 418 days. The results surprised even the researchers: None of the animals left the Galápagos Marine Reserve during the entire study period - even though the scientists had actually expected the animals to migrate to the distant western Pacific to reproduce.
Five of the nine tortoises remained near a single island throughout the study. The others occasionally moved between two or three islands - but only during the cooler months from April through October. A turtle named Ainoa traveled the farthest: originally tagged off San Cristóbal, she later moved on to Santa Cruz and finally to Isabela. On average, a single turtle’s range covered about 1,500 square kilometers, though there were significant differences between individual animals.
Site fidelity with an open-ended future
Nevertheless, the animals are unlikely to remain completely sedentary forever. Since female green sea turtles of the yellow form have not yet been observed laying eggs on Galápagos beaches, researchers assume that they will eventually return to their hatching beaches in the western Pacific - presumably every few years. The picture is more nuanced for the black form: Some females do lay eggs in the Galápagos and remain in the archipelago year-round, while others migrate to neighboring islands or even as far as feeding grounds off the coasts of Central and South America.
This finding has practical implications for conservation:
Since individual tortoises may rely on habitats spanning multiple islands, the researchers emphasize that water quality and migration corridors between the islands must be preserved throughout the archipelago - a single well-protected stretch of coastline is not enough if neighboring areas are left to deteriorate.
Sources:
Frontiers in Amphibian and Reptile Science
Alma College