Green sea turtles are famous for crossing oceans, but a group tracked by satellite in the Galápagos Islands did something researchers did not expect: none of them left the Galápagos Marine Reserve while their tags were transmitting. The peer-reviewed study in Frontiers, published Aug. 27 in Frontiers in Amphibian and Reptile Science and promoted by the publisher in late September, followed nine adult-sized yellow-morph green turtles tagged between 2015 and 2018.

These turtles belong to a genetically distinct form thought to have Indo-Pacific roots. Because yellow-morph turtles are not known to nest or mate in the Galápagos, scientists expected at least some to head toward distant breeding beaches. Instead, the tracking data showed strong loyalty to shallow coastal waters near the islands.

The practical takeaway concerns protection. If individual turtles rely on waters around several islands, safeguarding one favored feeding area is not enough. The researchers say habitat quality needs to be maintained across the whole archipelago.

Two Kinds of Green Turtle Share One Archipelago

Green sea turtles differ from the six other living sea turtle species because adults are mainly herbivores, grazing on seagrasses and algae, as NOAA Fisheries notes in its species profile. In the Pacific, scientists recognize two forms. Black-morph green turtles are associated with the eastern Pacific, while yellow-morph turtles are thought to have Indo-Pacific affinities.

The Galápagos is the only known place where both forms share the same waters, according to the publisher's summary of the research. There, they mingle and feed on similar marine vegetation. Young yellow morphs also tend to grow faster than young black morphs, hinting at physiological differences scientists have not fully explained.

"We expected them to migrate to distant beaches in the western Pacific to reproduce," said John W. Rowe, a biology professor at Alma College in Michigan and the study's corresponding author. Instead, he said, none of the satellite-tagged turtles even left the marine reserve.

Tracking Data Reveal Strong Ties to Home Waters

The team captured the turtles by hand in shallow water at four islands: Española, Floreana, Isabela and San Cristóbal. Seven were males, and two were females. Each received a transmitter that relayed locations through the Argos satellite system. Tracking lasted between 45 and 418 days, ending when a tag detached or stopped transmitting. Captures took place from August 2015 through November 2018.

Five of the nine stayed mainly around a single island. Four moved between islands, including a female named Ainoa who traveled from San Cristóbal to Santa Cruz and then to Isabela, the most extensive movement recorded. All of the inter-island travel took place between April and October, the cooler season in the Galápagos.

Home ranges varied enormously, from about 24 square kilometers (9 square miles) to more than 27,000 square kilometers (about 10,500 square miles). The middle value among the nine turtles was about 1,500 square kilometers (about 580 square miles). For comparison, the authors note that juvenile green turtles tracked in the Florida Everglades used areas averaging roughly 1,000 square kilometers, while most green turtle studies elsewhere report average home ranges below 85 square kilometers.

Limits That Shape the Headline Finding

The study is small, and the authors are explicit about its limits. Nine turtles is a modest sample, and tracking periods ranged from about six weeks to just over a year. The authors cautioned that their results are not evidence that the turtles "do not undertake trans-oceanic reproductive migrations."

Several factors could explain the stay-at-home pattern. Some turtles may not have been ready to breed during tracking, and some may have been near-mature rather than fully adult despite their size. If yellow morphs breed only every few years, a year of data could miss a migration entirely.

Coauthor Juan Pablo Muñoz-Pérez, a professor at Universidad San Francisco de Quito in Ecuador, said that because females of this form are not known to nest in the Galápagos, "we believe that they will eventually leave the area" to return to natal beaches in the western Pacific.

Argos positions also carry errors ranging from about 250 meters to more than 1.5 kilometers, which the authors say can inflate home range estimates. The largest range came from Ainoa, whose tag transmitted for only 45 days.

Conservation Stakes Across the Islands and Beyond

The Galápagos Marine Reserve, established in 1998, together with the Hermandad Marine Reserve created in 2022, covers nearly 200,000 square kilometers (about 77,000 square miles) of protected ocean, according to the study. The findings suggest the waters between islands may work as movement and foraging corridors that deserve attention alongside known feeding grounds.

Rowe said the quality of foraging habitat "should be maintained intact across all islands, and not allowed to degrade anywhere."

The work has U.S. ties beyond Alma College. Coauthors include a researcher from Turtle Island Restoration Network, based in Galveston, Texas, and the study drew logistical support from the Galápagos Science Center, a partnership between Universidad San Francisco de Quito and the University of North Carolina at Chapel Hill. The Galápagos National Park Directorate issued the research permits.

Green turtles have recovered in some regions, and the IUCN reclassified the species globally as Least Concern, down from Endangered, in 2025. The study's authors note that the species still faces many human-caused threats throughout its life cycle, and a global listing does not describe the status of every regional population.

What Readers Want to Know

What did the Galápagos turtle study find?

Nine satellite-tagged yellow-morph green sea turtles stayed within the Galápagos Marine Reserve for the entire time their tags transmitted, which ranged from 45 to 418 days.

Why did scientists expect the turtles to leave?

Yellow-morph green turtles are not known to nest or mate in the Galápagos, so researchers expected them to travel to distant breeding beaches, likely in the western Pacific.

Does this mean these turtles never migrate?

No. The authors caution that tracking periods may have been too short and some turtles may not have been ready to breed, so long migrations could still occur.

How many turtles were tracked?

Nine turtles, seven males and two females, were tagged at four islands between August 2015 and November 2018.

Why does the finding matter for conservation?

Some turtles used waters around several islands, so researchers say coastal habitat and the routes between islands need protection across the archipelago, not just at single feeding sites.

Are green sea turtles still endangered?

The IUCN reclassified green turtles globally from Endangered to Least Concern in 2025, but the species still faces many human-caused threats, and regional populations can differ.