9 tagged Galapagos sea turtles never once left the marine reserve

Nine adult green turtles carried satellite transmitters around the Galápagos for as long as 418 days, and not one of them crossed out of the Galápagos Marine Reserve. Biologist John W. Rowe of Alma College, who led the work, said the result ran against what the team expected. The researchers had anticipated long trips to distant western Pacific beaches to reproduce, he said, yet none of the satellite-tagged turtles even left the Galápagos Marine Reserve over the three years of the study.

The animals are yellow-morph green turtles, a color form of the species whose breeding grounds have never been located inside the archipelago, which is why the researchers watched for a long-distance departure at all. The study followed them from four islands and recorded where each one went.

The nine tagged turtles, from four islands

The roster comes from the paper in Frontiers in Amphibian and Reptile Science, whose first listed author is Juan Pablo Muñoz-Pérez of Universidad San Francisco de Quito in Ecuador. The team tagged seven males and two females between August 2015 and November 2018 at Española, Floreana, Isabela and San Cristóbal islands. The paper identifies all nine by name: Ainoa, Bernardo, Cristian, Jason, John, Leandro, Mike, Roberto and Sara. The transmitters were Wildlife Computers SPOT5 and SPOT6 units, plus KiwiSat S202 tags, all reporting through the Argos satellite system.

Tracking time differed a great deal from animal to animal. Cristian was followed for 367 days, Roberto for 296, Mike for 324 and John for 378, according to the paper, with the whole set spanning 45 to 418 days and averaging about 281. Funding came from the DOW Foundation, MIGRAMAR and Turtle Island Restoration Network, and Universidad San Francisco de Quito granted the ethics approval.

Tracking windows of 45 to 418 days behind the “never left” result

The paper’s wording is that “despite extended tracking durations, no individuals exhibited movements beyond the archipelago.” Rowe’s version, quoted by Discover Wildlife, adds the expectation that went unmet: the team anticipated the turtles would travel to distant beaches in the western Pacific to reproduce. The claim belongs to the tracked animals and their tracking periods. It covers nine turtles followed for between 45 days and about 14 months each, and the three years in Rowe’s quote refers to the span of the fieldwork, not to a continuous record on every animal.

Inside the reserve, the turtles used ground that varied enormously. The mean home range, measured as the 95 percent utilization distribution, was 1,498 square kilometers, with a spread of plus or minus 2,914 and individual values from 23.9 to 27,316 square kilometers. The authors describe “strong coastal site fidelity, with core areas concentrated in shallow nearshore habitats.” The largest range is about 1,140 times the smallest, so the average of 1,498 square kilometers hides one animal that barely left a patch of coast and another that covered a range larger than any single island in the archipelago, and the very large standard deviation is the paper’s own signal that the nine behaved differently from one another. Staying inside the reserve, in other words, did not mean staying put.

Inter-island moves between April and October

Some did travel between islands. The paper records Leandro moving between Isabela and Española, Bernardo and Sara between Isabela and San Cristóbal, and Ainoa across San Cristóbal, Santa Cruz and Isabela. It adds that every inter-island movement recorded took place between April and October, which it ties to the cooler season in the Galápagos.

The finding sets these animals apart from other Galápagos green turtles. The Charles Darwin Foundation notes that the East Pacific green turtle nests across more than 100 beaches in the archipelago, and that after nesting season turtles travel to feeding grounds as far as Nicaragua and Chile. The foundation’s account of the two morphotypes says the black morph nests in the islands while the yellow morph is found only at feeding sites and is thought to migrate to the Indo-Pacific region to reproduce.

Against that background, a negative result carries weight. NOAA Fisheries describes the green turtle as a highly migratory species that nests in more than 80 countries and turns up in coastal waters of more than 140, so a set of animals that spends most of a year inside one reserve, some of it within a single island’s shallows, departs from what the species is known for. The paper reports no tracks that headed for the open Pacific, in any season, from any of the four tagging islands.

The authors state that neither female nor male yellow-morph turtles are known to reproduce in the Galápagos. Where these nine would eventually breed, and whether the two tagged females would ever head west, remains unanswered by tracks that stopped at 418 days at the longest.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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