Tropical sea turtles discovered nesting in California for the first time in recorded history

By Laura Paddison, CNN

(CNN) — Sea turtles usually found in the tropics have been spotted nesting on California beaches — a historical first, according to officials.

Olive ridley sea turtles are one of the smallest of the sea turtles and have distinctive olive-green, heart-shaped shells. They are typically found in tropical parts of the Pacific, Indian and Atlantic Oceans. But this month, two have come ashore in California.

An olive ridley turtle was seen digging a nest near Seal Beach National Wildlife Refuge in northwest Orange County last week, according to the US Fish and Wildlife Service.

A few days later, a nesting olive ridley was spied near the Huntington Beach Pier, also in Orange County. Originally, it was believed they were the same turtle, but an expert analysis of body shapes and unique shell patterns confirmed these were two different turtles.

The sightings mark “the first-ever documented natural sea turtle nesting on the US West Coast,” the National Oceanic and Atmospheric Administration said in a social media post.

Olive ridley turtles are known for mass nesting, called “arribada,” where thousands come ashore at the same time to lay their eggs on a certain beach — a phenomenon that’s been observed in countries such as Costa Rica and Mexico. But it’s more common for the turtles to nest in a solitary way, which is what appears to have happened in California.

Scientists are still working to understand what pushed the turtles northward and whether this is an anomaly or potentially a more long-term expansion of their range as the human-driven climate crisis warms the oceans.

Their behavior was very likely influenced by the current super El Niño weather pattern, which has driven up ocean temperatures, said Jeffrey Seminoff, leader of the Marine Turtle Ecology & Assessment Program at NOAA.

But this is likely not the only reason. Sea turtles navigate the oceans “using multiple internal and environmental cues, including their own internal compass — sort of an on-board GPS — as well temperature, wave direction, time of year, etc.,” Seminoff said.

He believes a confluence of factors, including sustained warm water and “malfunctioning GPS,” likely led them to think they were coming ashore at nesting beaches in Mexico.

Another theory is that Pacific storm activity could have pushed the turtles off course. The Pacific Ocean has been particularly busy recently as the exceptionally warm water brought by El Niño supercharges its hurricane season.

“Nothing is off the table in terms of causation. It will be so hard to unravel the specific reasons,” Seminoff said.

Each olive ridley nest usually contains around 100 eggs, and the sex of the baby turtles is affected by temperature. Warmer temperatures tend to produce more female turtles. For olive ridleys, temperatures around 87 degrees Fahrenheit and above will mean almost all hatchlings will be female.

An interagency team will monitor the California nests for the next 45-60 days, the typical incubation period. The nest sites have already been fenced off and people are being asked to give them space and avoid disturbing them, to give the baby turtles the best chance of hatching. In the US, sea turtles are protected under the Endangered Species Act.

“As animals adapt in unexpected ways to changes in their natural world, humans will need to adapt and make space to ensure endangered and threatened species are given a fighting chance,” said Jeff Flocken, president and CEO of the Aquarium of the Pacific, a non-profit institution, in a statement.

“If they successfully hatch, these baby turtles will likely one day return to nest to carry on future generations on these very same beaches, giving us a remarkable opportunity to help a species expand its range and thrive.”

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