A grunion run is a natural event where small, silvery fish called California grunion come ashore on sandy beaches to spawn. This occurs on specific nights along the California coast, drawing observers. Unlike most fish, grunion temporarily leave the water. This phenomenon highlights a specialized reproductive strategy adapted to the dynamic intertidal zone.
The Grunion Spawning Phenomenon
The California grunion, Leuresthes tenuis, leaves the ocean to lay eggs on the beach. These fish come ashore at night, following the highest tides associated with new and full moons. As waves recede, female grunion ride them onto the sand, twisting their bodies tail-first to dig into the wet substrate until partially buried.
Once the female is nestled in the sand, she deposits her eggs, while several males may curve around her to release milt, which fertilizes the eggs. This process can take as little as 30 seconds, though some fish may remain on the beach for several minutes before returning to the sea with the next wave. Females can lay between 1,600 and 3,600 eggs in a single spawn and may repeat this process up to six times in a season. The eggs then incubate in the moist sand for about 10 days, safe from aquatic predators, until the next series of high tides washes them out to sea, triggering them to hatch.
Finding and Observing Grunion Runs
Grunion runs occur seasonally in California, from March through August, with peak spawning from late March to early June. The California Department of Fish and Wildlife (CDFW) publishes schedules of predicted run dates, based on lunar cycles and tide charts. Runs are not always guaranteed even on predicted nights, as environmental factors can influence their appearance.
To observe a grunion run, plan for dark, moonless nights and arrive after the high tide has begun to recede. Common locations along the Southern California coast include beaches in San Diego, Orange, and Los Angeles counties, such as Cabrillo Beach, Santa Monica State Beach, and Malibu. Observers should use flashlights sparingly, as bright lights can deter the fish, and patience is often required since runs can be unpredictable.
Rules for Grunion Observation and Collection
For individuals aged 16 and older, a valid California sport fishing license is required to collect grunion. Grunion may only be taken by hand; nets, traps, or other equipment are prohibited, and digging holes to entrap them is not allowed. A closed season for grunion collection runs from April 1 through June 30, during which observation is permitted but handling or taking the fish is forbidden.
During the open season (March, July, and August), a daily bag and possession limit of 30 grunion per person is in effect. Prioritize responsible viewing and minimize disturbance to the spawning fish, especially during the closed season, to support conservation efforts for grunion populations.