Ten weeks ago two green sea turtles were released off the coast of Australia carrying satellite trackers. One of these immediately headed east for 47 days almost directly towards Tonga. Then, very suddenly, she pulled a 180 and noped her way out of there. The next day, the Hunga Tonga-Hunga Ha'apai volcano erupted, setting off the tsunami and rain of ash that has devastated nearby islands.
Jennifer Gilbert of the Cairns Turtle Rehabilitation Center (CTRC) told IFLScience it is “speculative” to declare that Tilly the turtle knew what was coming, but the map of her journey certainly doesn't look like a coincidence. Moreover, as she was heading back towards the Great Barrier Reef a small earthquake struck north Queensland, It wasn't large enough to do damage, but coincided with Tilly diverting her path once again.
“I'm going to do an observational paper,” Gilbert told IFLScience. “There has been nothing done on turtles and seismic detection previously.” On the other hand, Gilbert said, studies have been published on the capacities of whales, dolphins, seals, and even goats to detect seismic activity before it occurs, so Tilly may have had some swifter company on her return journey.
Tilly's course changes are the latest twist in a film-worth life story. Volunteers checking the success rate of a turtle nest found most either never hatched, or made it out of the nest for the terrifying dash for the sea highlighted in a thousand nature documentaries. However, two green sea hatchlings were exhausted by their failed attempts to scramble up from the bottom and would have died without human intervention.
The two were brought to CTRC and named Tilly and Sammy, although Gilbert told IFLScience sex can not be identified until they are at least 20 years old. “It was very touch and go for a while” whether the pair would survive, Gilbert told IFLScience. Eventually, both flourished. Traditionally rescue turtles are released when they reach 45 centimeters (18 inches) in size, but by the time that happened COVID-19 impeded trips to the continental shelf, where rescue turtles are released.
By the time the release occurred the turtle twins were three years old and considerably larger, allowing the CTRC to put more powerful trackers on them. Even before the eruption, Gilbert hoped this would prove scientifically useful. Flatbacks aside, sea turtles who survive their journey through the shallows head for the continental shelf, not coming close to shore until they are 5-10 years old. “We call them the lost years,” Gilbert said. “We don't really know what they do then.”
One thing researchers had not expected was for a 3-year-old turtle to head straight over deep water, apparently, in a quest for reefs thousands of kilometers away, rather than the much more convenient outer Great Barrier Reef. “Those waters are full of predators,” Gilbert said. “She was definitely heading for the Soloman Islands or New Caledonia, but we don't know why.” Even in the light of Aesop's fable about Testudines' unexpected territory-covering capacity, the fact Tilly has clocked up 3,000 kilometers (1,800 miles) in 73 days astonished Gilbert.
Unfortunately Sammy's tracker stopped working 10 days after his release, which could have been an equipment malfunction or an unfortunate encounter with a shark. The CTRC had no other turtle trackers in the area at the time, and Gilbert said apparently the same was true of other Australian research institutes, so we don't know if other turtles were similarly prescient.
Much as it might have benefited the people of Tonga to have known of the eruption when Tilly apparently did, Gilbert told IFLScience, “I don't think you could use turtles as a prediction device. You can't tell a turtle where to go, or even predict what they will do. They have a mind of their own.”