Quirks & Quarks

Researchers solve the mystery of loggerhead turtle's lost years

Loggerhead sea turtles breed in Japan, but some cross the ocean to feed in Mexico. Now, researchers know how they make that trip — and why some stay behind.

Loggerhead sea turtles breed in Japan, but some cross the ocean to feed in Mexico.

By tagging 200 North Pacific Loggerhead Sea Turtles and following them for 15 years, researchers were able to find out how they travel more than 9000 kilometers from their breeding grounds to their foraging grounds. (Ralph Pace)

By satellite tagging hundreds of loggerhead sea turtles — and creating the largest data set of its kind — researchers now have a new understanding about the mysterious migrations of these endangered turtles.

The breeding grounds for the North Pacific Loggerhead sea turtle are on the beaches of Japan. Once they hatch, the turtles disappear into the ocean for decades before ultimately returning to breed. Scientists referred to this time as their 'lost years' because it was unclear where they went. 

"For a long time we've known that the loggerhead sea turtles are on both sides of the Pacific," Dana Briscoe told Quirks & Quarks host Bob McDonald. "But we thought that there were two entirely separate, distinct populations because it seemed unimaginable that such a small creature could cross an entire ocean basin that's greater than 9000 kilometres in distance."

By tagging 200 sea turtles and tracking them for 15 years, the team was able to confirm that these are indeed the same turtles. They were also able to solve the mystery of why only some turtles cross the ocean, while others stay behind.

Satellite tracks of 231 juvenile North Pacific loggerhead sea turtles (light gray), including six (various colors) that migrated to the coastal waters of Baja California. (Dana Briscoe, et al. / Frontiers in Marine Science)

They found that during years where the ocean is warmer due to El Nino or marine heatwaves, a 'thermal corridor' opens up allowing turtles to easily make their way across.

"If a turtle happens to be at the right spot at the right time in the eastern Pacific, they're essentially queued up to take advantage of these corridors that may open under certain ocean conditions," said Briscoe.

The study was published in the journal Frontiers in Marine Science.

Dana Briscoe is a marine scientist with the Stanford Woods Institute for the Environment, and the Cawthron Institute in New Zealand. You can listen to her full interview with Bob McDonald at the link above.


Produced and written by Amanda Buckiewicz

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