Mobs of tuna crabs descend on Southern California waters. What’s going on?

Little red crustaceans pepper the shallow depths by the San Diego shoreline. The tuna crabs are back.

Tuna crabs, named after their most common predator — the tuna fish — have been seen by the thousands in Southern California in recent months. Charlotte Seid from Scripps Institution of Oceanography told NBC 7 San Diego that while this migration used to happen once every few years, according to the National Oceanic and Atmospheric Administration, it has been happening far more often in recent years.

Seid told NBC 7 that this could be due to a heat wave down south caused by El Niño and the changing tide that carries them up north from Baja, Mexico.

“It’s not that the crabs are deliberately making their way to us,” Seid told the outlet. “They live in those waters and get swept up sort of like birds outside of their migration route.”

That’s because these crabs are not great swimmers, according to National Geographic.

While the red pinchers have been making more frequent visits, they never stick around long.

“The crabs start to die because the local waters are much cooler,” research scientist Michael Shane told ABC News in 2015.

According to CBS8, this is a great opportunity for divers and snorkelers to get a glimpse of the swarms not far from the beach.

Anyone who wants to see them should hurry. They’ll likely be gone by June.

But, experts warn people not to eat them, according to CBS8. They contain toxins that may be harmful to humans.

This story was originally published May 17, 2024 at 11:26 AM with the headline "Mobs of tuna crabs descend on Southern California waters. What’s going on?."