Sex on the beach is best in the dark. Grunion knows that. Every spring and summer, a few days after a full moon or new moon, the small, silvery fish wash ashore to spawn in their thousands on the beaches of Southern California.
Like the swallows’ annual return to San Juan Capistrano or the California gray whale migrations offshore, grunion races remind us that wildlife survives in a vast million-strong city. Although unknown to many, grunion races are a local fixture. Coastal Indians once relied on them for food. In the 1960s, Frank Zappa wrote and recorded an instrumental song called “Grunion Run”, which contained the sound of a guitar connected to a fuzzbox.
On a recent evening, about 100 visitors to Cabrillo Beach in San Pedro were voyeurs to the mating dance that takes place shortly after high tide. It unfolds like a clockwork. One moment the beach is empty. Then a wave crashes in and deposits the wildly teeming fish on the wet sand to lay and fertilize countless eggs before retreating into the ocean.
Basically, the females dig nests with their tails and lay eggs in the sand. Up to eight males attempt to mate with each female by curling their bodies around her. Spleen flows down through the female’s body to fertilize the eggs. During the night, more grunion glide up the beach and merge over the surf line.
How the grunion knows when to run is still a mystery. It can be the draft of the tide or the position of the moon. The eggs develop over 10 days and hatch with the next high tide. Most of the chicks are eaten by other fish and shorebirds higher up in the food chain.
The fish are unique to southern California and northern Baja. They are essentially odorless. Most nights, people are legally only allowed to see the fish. Open nights take place during the season and people with a valid fishing license can catch an individual limit of 30 fish in hand. Beach erosion and coastal development threaten the fish’s spawning habitat, although experts say the species currently appears to be viable.
The next grunion race is expected to take place in San Pedro on June 16th.