Scientists expected these Galápagos sea turtles to wander. They stayed put.
The research followed yellow-morph green sea turtles in the Galápagos, and discovered they stay close to a few islands throughout their lives instead of wandering far across the open ocean. Published in Frontiers in Amphibian and Reptile Science, the findings show the turtles seldom travel beyond the Galápagos Marine Reserve.
What the Turtles Did Instead
These creatures are renowned for their lengthy oceanic migrations. To guide themselves, they rely on the planet’s magnetic field, the sun, and ocean currents. They travel great distances in search of sustenance, then return to the very sites of their birth to breed.
The yellow-morph green sea turtles did not follow the usual pattern. Across three years of satellite tracking, none of the tagged turtles left the Galápagos Marine Reserve. Instead, most remained within a few kilometers of a single island.
“Here we show that ‘yellow-morph’ green sea turtles – one of two genetically distinct forms – occupy individual foraging areas which span one or more islands in the Galápagos,” said Dr. John W Rowe, a professor at Alma College and the study’s corresponding author. “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.”
Two Kinds of Turtle, One Place
Young green sea turtles eat a mix of plants and animals, but the adults switch to a vegetarian diet. As the turtles mature, their meals change from small creatures and vegetation alike to seaweed and algae alone. Green sea turtles are the only living sea turtle species where the adults eat mostly plants.
Two genetically distinct forms of green sea turtle exist, and the Galápagos is the only known place where both coexist. Yellow morphs are generally found across tropical and subtropical parts of the western Pacific, while black morphs occur in the eastern Pacific west of the Americas and south of southern California.
This is the only place where the two forms coexist, eating from the same marine vegetation and mixing among themselves in shared waters.
How the Turtles Were Tracked
In 2015, Rowe and his colleagues caught nine adult turtles in shallow water near four islands. Seven were males and two were females. The team gave the turtles nicknames — Bernardo, Sara, Leandro, Ainoa — and attached electronic transmitters that sent location signals to the low orbit Argos satellite network.
For as many as 418 days, the turtles were tracked. The monitoring usually came to an end when a tag either detached itself or stopped transmitting signals.
The findings pointed toward a clear preference for waters close to land. Nearly all turtles kept close to the shore, rarely moving more than a few kilometers offshore, with some going as far as 25km from the islands. Out of the group, five of the nine individuals were found to spend the majority of the study period near a single island.
Leandro went between Isabela and Española, while Bernardo and Sara went between Isabela and San Cristóbal. Among the four, Ainoa did the longest journey, going from San Cristóbal to Santa Cruz and then on to Isabela.
A Seasonal Pattern
The scientists observed turtles traveling between islands solely during the cooler months, from April through October. The average home range for each turtle spanned 1,498 square kilometers, yet the size of these territories varied widely among individual animals.
These turtles appear to stay close to where they were tagged, according to the tracking data. Still, the researchers stress that their findings cover just a short stretch of the animals’ lives. The data do not rule out longer journeys taking place at other points in time, which might simply have fallen outside the study’s window.
The researchers believe that female yellow-morph green sea turtles will eventually leave the Galápagos beaches to return to their natal beaches in the western Pacific, because these females are not known to lay eggs there. That possibility holds special weight for females.
Dr. Juan Pablo Muñoz Pérez, a professor at the Universidad San Francisco de Quito in Ecuador, said that “In contrast, some female black-morph green turtles do nest in the Galápagos: depending on the individual, those may be year-round residents in the archipelago, travel to other nearby oceanic islands, or even to feeding grounds off Central and South America,”.
What the Findings Mean for Conservation
How the turtles are protected could depend directly on these findings. Since certain turtles travel between several islands, guarding just one preferred feeding spot might fall short.
The scientists stressed the need to safeguard the coastal waters and channels linking islands that the turtles rely on as they travel across the archipelago.
Rowe said “Since individual turtles may rely on waters around multiple islands, the quality of habitat that is available for foraging should be maintained intact across all islands, and not allowed to degrade anywhere,”.
Key Facts Box
- Study: Movements of yellow-morphotype green turtles
- Publication: Frontiers in Amphibian and Reptile Science
- Authors: Juan Pablo Muñoz-Pérez, Daniela Estefania Alarcón-Ruales, Lyndsey K. Tanabe, Catherine E. Hart, Maike Heidemeyer, Todd Steiner, Randall Arauz, Carlos A. Valle, John W. Rowe
- Tracking period: Up to 418 days per turtle
- Distance traveled: Up to 25km from shore
- Home range: Average 1,498 sq km
- Islands tracked: Isabela, San Cristóbal, Española, Santa Cruz
The turtles’ behavior was unexpected, and the study’s authors admit as much. But the data are clear: these turtles stayed close to home, season after season, island after island. The surprise is real, and the science backs it up.
Researchers were surprised by what the turtles ended up doing, and the tale they tell about it is a good one.
Source material: “Scientists expected these Galápagos sea turtles to wander. They stayed put,” ScienceDaily.
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