The Turtles That Didn’t Go Home: What Nine Tagged Galápagos “Yellow Morph” Green Turtles Reveal About a Missing Migration
Satellite tracking reveals that these little-known turtles depend on the Galápagos Marine Reserve for food, shelter—and connections between islands.
If you’ve ever snorkeled the coves of the Galápagos or dived the waters of Cocos Island National Park in Costa Rica, you have probably seen a green sea turtle drifting past, dark and almost black-shelled. But scattered among these familiar black-morphotype turtles is a rarer, paler cousin: the yellow-morphotype green turtle. We have long known it exists, but little else.
Yellow-morph green turtles are normally found in the warm waters of the western Pacific and Indo-Pacific, far from the colder temperatures found around the Galápagos. While thousands of green turtles nest in the Galápagos, yellow-morph turtles have never been seen nesting there or anywhere else in the Eastern Pacific.
A new study by a team of scientists (including TIRN founder Todd Steiner) is shedding light on one of the rare residents of the Galápagos Islands: the yellow-morph green turtle (Chelonia mydas). Published in Frontiers in Amphibian and Reptile Science, the study tracked nine adult-sized yellow-morph green turtles (seven males and two females) using satellite transmitters. The turtles were captured and tagged around four Galápagos islands and monitored for periods ranging from 45 to 418 days.
Home is Close to Shore
While four of the turtles moved between different Galápagos islands, the other five remained in the shallow waters near the island where they were tagged, and none left the boundaries of the Galápagos reserve.
The turtles’ movements also varied enormously. Their estimated home ranges averaged about 1,498 square kilometers, although individual ranges varied from just 24 square kilometers to more than 27,000 square kilometers.
Perhaps the most important finding is that all nine turtles remained within or near the Galápagos Archipelago during their tracking periods, even turtles monitored for more than a year. None traveled beyond the archipelago during the study.
Clearly, the Galápagos Marine Reserve functions as an important coastal foraging and mixing habitat for yellow-morph green turtles.
That makes protecting not only individual feeding areas, but also the connections between coastal habitats and islands, critically important.
Green turtles are long-lived and may not reach sexual maturity until 20 to 50 years of age. Yet they are known to return to the same nesting beaches where they hatched, even after long migrations of hundreds to thousands of miles from their foraging grounds.
Yellow-morph green turtles remain poorly understood and are a missing piece of the green turtle puzzle.
Unlike the more familiar black-morph green turtles of the Eastern Pacific, their reproductive ecology remains unresolved. Neither males nor females of this morphotype have ever been found breeding in the Galápagos, and where they ultimately come from—and where they go to reproduce—remain unknown.
There is still much to learn, and solving the mystery of where yellow-morph turtles go to nest may have to wait for longer battery life and better attachment technology. Currently, satellite transmitters last only a year or two, while green turtles may spend many years feeding and growing before leaving their foraging grounds for their natal nesting beaches.
For now, the message is clear: the Galápagos Marine Reserve is more than a boundary on a map. For yellow-morph green turtles, it is a living network of coastal feeding grounds and travel corridors.
Protecting the quality and connectivity of those waters is essential to ensuring that these remarkable turtles continue to thrive. With better knowledge, we will hopefully also be able to protect their migration corridors when they leave the protected Galápagos reserve.
The study, “Movements of yellow-morphotype green turtles (Chelonia mydas) in the Galápagos Marine Reserve,” was authored by Juan Pablo Muñoz-Pérez, Daniela Estefania Alarcón-Ruales, Lyndsey K. Tanabe, Catherine E. Hart, Maike Heidemeyer, Todd Steiner, Randall Arauz, Carlos A. Valle and John W. Rowe.
