Unveiling the Enigmatic Ritual: Witnessing the Astonishing Spawning Behavior of Grunion Fish on California’s Beaches

These fish are famous for their remarkable spawning behavior, which evokes an “I don’t believe it!” response from people seeing or hearing about it for the first time.

Grunion leave the water at night to spawn on beaches during the spring and summer months. For four consecutive nights, beginning on the nights of the full and new moons, spawning occurs after high tides and continues for several hours. As waves break on the beach, grunion swim as far up the slope as possible. The female arches her body and excavates the semi-fluid sand with her tail to create a nest. She twists her body and digs into the sand until she is half buried, with her head sticking up. She then deposits her eggs in the nest. Males curve around the female and release milt. The milt flows down the female’s body until it reaches and fertilizes the eggs. As many as eight males may fertilize the eggs in a single nest. After spawning, the males immediately retreat toward the water while the female twists free and returns with the next wave. While spawning may only take 30 seconds, some fish remain stranded on the beach for several minutes.

Spawning occurs from March through August, and occasionally in February and September. Peak spawning is late March to early June.

Eggs are deposited during the highest tides of the month and incubate in the sand during the lower tides, when they will not be disturbed by wave action. The eggs are kept moist by residual water in the sand. They hatch about 10 days later, during the next high tide series, when they are inundated with sea water and agitated by rising surf.

While grunion spawn on many beaches in southern California, the California Department of Fish and Wildlife does not recommend any particular beach because of changing safety conditions and local curfews. One of the best ways to find out which beaches have had recent runs is to call the state and county beach lifeguards who can often tell if spawning has taken place. There is a grunion program offered to the public at Cabrillo Beach in San Pedro on several nights of the season. Visit the Cabrillo Marine Aquarium for more information.

Frequently asked questions, information on volunteer programs, and other information may be found at www.grunion.org.