The California grunion (Leuresthes tenuis) is a small, silvery fish known for a unique reproductive ritual. Unlike nearly all other fish, the grunion leaves the water entirely to spawn on sandy beaches. This event, known as a “grunion run,” involves thousands of fish riding the waves ashore to deposit and fertilize their eggs in the wet sand.
The Critical Timing
The grunion run is a predictable event, occurring exclusively at night during the spawning season (March through August). The timing is governed by the lunar cycle and associated tides. Spawning runs occur for three to four consecutive nights following the full and new moons, which generate the highest tides.
The fish must deposit their eggs high enough on the beach to remain undisturbed by the ocean. Runs begin only after the highest tide of the night has peaked and the water level is starting to recede. This placement ensures the eggs are covered and protected by the sand until the next major tide series. Runs generally start shortly after the peak high tide and can last for one to three hours.
If the grunion spawned on an ascending tide, the eggs would be washed out prematurely by the subsequent rising water. By utilizing the highest tides of the month, the fish guarantee the eggs are buried deep enough to incubate in the moist sand for approximately ten days, safely above the reach of normal daily tides.
The Spawning Mechanism
Once carried onto the beach, the spawning process begins rapidly on the wet sand. The female fish swims or flops as far up the shore as possible, then arches her body and uses her tail to excavate a small nest. She twists tail-first into the soft sand until she is partially buried, with only her head visible above the surface.
The female then deposits her clutch of eggs, which can number between 1,600 and 3,600, a few inches below the sand’s surface. Simultaneously, one or more male grunion wrap themselves around the female’s exposed body. The males release their milt, which flows down the female’s body and into the sand to fertilize the eggs.
This entire process of egg deposition and fertilization can take as little as thirty seconds. Once the eggs are fertilized, both the males and the female wriggle free from the sand and ride the next incoming wave back to the ocean. The eggs remain buried, protected from drying out and predators, until the next series of extremely high tides returns to wash them out and trigger their hatching.
Geographic Range and Observation Rules
The natural geographic range of the California grunion extends from Point Conception in Santa Barbara County, California, southward to Punta Abreojos in Baja California, Mexico. The most reliable viewing opportunities occur along the sandy beaches of Southern California. Observers seeking to witness a run should consult official schedules published by state agencies, which predict the two-hour window when spawning is most likely.
A valid California recreational fishing license is required for those aged sixteen and older who wish to catch grunion. The open season is restricted to March, July, and August; April, May, and June are closed to protect the peak spawning period. During the open season, the daily bag and possession limit is thirty grunion per person.
Grunion may only be taken by hand; the use of any appliance, such as nets, seines, or buckets for scooping, is prohibited. Furthermore, observers are not permitted to dig holes in the sand to entrap the fish. All participants should minimize light disturbance and noise to allow the fish to complete their spawning ritual with minimal disruption.