Southern California grunion have their moment in the sand

Find the right beach this weekend and you could be treated to the site of thousands of small, silvery fish, wriggling around in the sand. It's the annual running of the grunion.

"This is the only place in the world where you can see them," says Karen Martin, a professor of biology at Pepperdine University.

The sardine-sized fish have a unique spawning ritual. During high tide, the females swim up on the beach, dig their tails into the sand and lay their eggs. Males wrap themselves around the female as they deposit their sperm.

When they're done, the adults return to the water — but their eggs stay on beach, under the sand. At the next set of high tides, the water washes the eggs out into the ocean, where they hatch.

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The grunion season lasts from March to August, generally peaking in April or May, when it's illegal for people to catch or take the fish.

"Usually, this is the best time of year to go," Martin says. "They can run undisturbed, so they won't be frightened away by what people are doing on shore." 

So how can you find the grunion of Southern California?

First, you need to know when to go. 

The ideal time is at night. Grunion spawn for the four consecutive nights beginning on the nights of the full and new moons. The California Department of Fish and Wildlife has handy charts listing the best dates and times to see them. Martin adds that the best window of time to see them is 15 minutes before high tide until about two hours after.

Even then, be prepared for uncertainty.

"We never know what's going to happen. We never know how long it's going to go. No one knows but the fish what's going to happen," Martin says. 

Now, you have to find a beach.

"Where people surf is usually a good choice," Martin says. "It's the same kind of wave that the fish like. They're the original surfers."

Grunion have been spotted from San Diego all the way up to Tomales Bay north of San Francisco, but their prime breeding ground is Southern California. They're happy to do it on any "open, gently-sloping, sandy, wave-swept beach in southern California," according to the Department of Fish and Wildlife. 

Martin and her fellow contributors to Grunion.org won't recommend specific beaches — aside from urging grunion seekers to find a beach where they feel safe at night and to not cross private property or do anything illegal.

One more piece of advice: Respect the grunion. 

"They're just great Californians," Martin says. "They love the beach. They love the surf. They like all the things we like. It's the California lifestyle."