Galápagos 'Yellow' Sea Turtles Surprise Scientists by Staying Put

Sea turtles are famous wanderers, guided by Earth's magnetic field, ocean currents and the sun as they roam for food before returning to their birth region to breed. So scientists were surprised by a Galápagos population that barely leaves home.

The animals are "yellow-morph" green sea turtles (Chelonia mydas), one of two genetically distinct forms of the species, according to a new study in Frontiers in Amphibian and Reptile Science. "We expected them to migrate to distant beaches in the western Pacific to reproduce, yet interestingly, none of our satellite-tagged turtles even left the Galápagos Marine Reserve over the three years of our study," said Dr. John W. Rowe of Alma College, the study's lead author.

Green sea turtles are the only one of seven sea turtle species that is mainly vegetarian as adults, eating seagrasses and algae. Yellow morphs live in the tropical western Pacific, while black morphs live in the eastern Pacific below Southern California. The Galápagos is the only place both coexist, sharing the same food plants, and yellow morphs grow faster than black morphs when young — hinting at unexplained physiological differences.

In 2015, Rowe's team caught seven adult males and two adult females off four islands in the Galápagos Marine Reserve and tracked them by satellite for up to 418 days. The turtles stayed in shallow coastal water. Five of the nine stayed near a single island, while others moved between islands, only in the cooler months from April to October. Average home range was 1,498 square kilometers, varying by turtle.

Co-author Dr. Juan Pablo Muñoz Pérez of Ecuador's Universidad San Francisco de Quito said female yellow morphs are not known to nest on Galápagos beaches, so they are expected to leave for natal beaches in the western Pacific, unlike some female black morphs, which do nest there and may stay year-round. The team said habitat quality must stay intact across every island turtles use.