Migrating Sea Turtles Actually Have A Pretty Poor Sense Of Direction

'Has anybody seen the Sargasso Sea? I'm sure I left it here.' – Disorientated sea turtle, 2022. Image credit: Rich Carey/Shutterstock.com

Hawksbill sea turtles will migrate long distances to reach foraging and nesting sites, but how do they know where they’re going? According to new research, they probably don’t.

The travel routes of migrating hawksbills (Eretmochelys imbricata) were mapped using GPS in a new study published in the Journal of the Royal Society Interface. Using models, the authors hoped it could try and solve the “long-standing enigma,” as they describe it, as to how some animals navigate their way across the ocean.

Looking at distances of tens to thousands of kilometers, they sussed out what the most likely routes between sites of interest would be if some kind of mapping system was used to work it out. They then compared this to the actual movements of wild hawksbill sea turtles traveling after mating season.

The sea turtles’ routes were often found to be circuitous paths: long and complicated ways of traveling from point A to point B. This meant they were traveling considerably longer distances than a bee-line route between two points, with one turtle swimming 1,306.2 kilometers (811.6 miles) when the fastest way would have only clocked 176.4 kilometers (109.6 miles).

“The navigational imperfection of turtles was evident right at the start of their oceanic migration, with their initial departure directions tending not to be target orientated, as is often the case with birds,” wrote the study authors.

Geomagnetism has been floated as a way in which turtles might reach isolated destinations while swimming in the oceans. However, based on their methodology the authors of this new paper suggest instead that the turtles have only basic map sense while using cues to correct and redirect themselves.

“It appears that turtles have a crude map with a resolution of many tens or even a few hundred kilometres and often it is only when they are well off track that they reorient,” they write. “Sea turtles locate isolated targets through a roughly target-oriented ocean crossing, open ocean course corrections and then localized search closer to the target.”

The complex and challenging life cycle of a turtle demonstrates how their ability to navigate between food and breeding sites is just one of many battles they face in surviving to adulthood.

While traveling over seven times the necessary distance between two points (like our aforementioned 811-mile turt) might not seem terribly adaptive, there could be some benefits to the approach. One, the authors suggest, is that these navigational imperfections might lend themselves well to coping with the influence of climate change on coastal habitats.

Sea-level rise associated with the climate crisis threatens present-day nesting beaches, but a more trial-and-error approach to seeking suitable nesting sites might enable sea turtles to find new beaches in place of lost ones. The same approach might make it easier to stumble across undiscovered foraging sites.

Hawksbill turtles might only have a “relatively crude map sense in the open ocean,” say the authors, but what they lack in navigational skills they may make up for in target searching. This flexible approach means they sometimes take the excessively scenic route, but they might just track down life-sustaining habitats on the way.

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