June 17, 2015 4:55 PM EDT

Beachgoers in southern California expecting the typical pristine shores may have been surprised to find the coast dotted with thousands of tiny red crabs in recent weeks.

Scientists say that the tuna crabs, typically around three inches in length, are typically found further South in waters adjacent to Mexico. They likely made their way North as a result of unusually warm water in the Pacific Ocean, in part due to the El Niño weather pattern. Because they spend time swimming through the water, rather than on the seafloor, they’re affected by winds and currents that may push them to shore.

This isn’t the first time tuna crabs have appeared on California shores, but it’s certainly not a regular occurrence. Warm currents from the South every five years may be the cause, according to the Los Angeles Times.

Write to Justin Worland at justin.worland@time.com.

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