The Grunion Run is a unique natural event where small, silvery fish called grunion come ashore on sandy beaches to spawn. Unlike most fish, grunion completely leave the water to lay their eggs directly in the wet sand. This mass beaching draws observers to Southern California and Baja California beaches, creating a mesmerizing display as thousands of fish cover sections of the shore, making it a popular wildlife viewing opportunity.
The Unique Biology of Grunion Spawning
The California grunion (Leuresthes tenuis) adapts its spawning to precise tidal and lunar cycles. These fish, typically five to six inches long, rely on the highest tides of the month, occurring after new and full moons, to access the upper reaches of sandy beaches. Spawning takes place on four consecutive nights following these peak tides, one to three hours after the high tide begins to recede. This timing allows eggs to be deposited above subsequent lower tides, protecting them from immediate wave action.
As a wave recedes, female grunion are carried onto the sand. Each female arches her body, using her tail to dig into the semi-fluid sand until she is half-buried, head up, creating a nest. She then deposits between 1,600 and 3,600 eggs. Simultaneously, one or more males, often up to eight, curve around the female and release milt (sperm), which flows down her body to fertilize the eggs. This entire process can take as little as 30 seconds, though some fish may remain on the beach for several minutes before returning to the ocean with the next wave.
The fertilized eggs remain buried in the moist sand, incubating for 10 to 12 days. Hatching is triggered by the agitation and inundation of the next series of high tides, freeing the larvae to be washed out to sea.
Predicting and Finding a Grunion Run
Predicting a grunion run involves understanding their reliance on the lunar cycle and specific tidal conditions. Grunion runs occur from March through August, with peak spawning activity from late March to early June. The California Department of Fish and Wildlife (CDFW) publishes schedules of expected runs, available through their website. These schedules provide two-hour intervals when spawning may occur, starting after high tide. The second and third nights of a four-night spawning period are usually the most active.
While CDFW does not recommend specific beaches due to changing conditions, grunion runs can happen on most open, gently sloping, sandy beaches in Southern California and Northern Baja California. Popular locations include beaches in San Diego, Orange, and Los Angeles counties, such as Cabrillo Beach, Huntington Beach, and Santa Monica Beach. For local information on recent runs, contacting state and county beach lifeguards can be helpful. Check local curfews and regulations for specific beaches before planning a visit, as some areas may have restrictions on access during late-night hours.
Observing and Protecting Grunion
Observing a grunion run requires patience and guidelines to avoid disturbing the fish and their spawning process. Arrive quietly and avoid sudden movements, as grunion are sensitive to light and vibrations. Using red-filtered flashlights is recommended, as white lights can disorient the fish and deter them from coming ashore. Remain at a respectful distance to allow grunion to complete their natural behavior.
Regulations protect grunion populations. A California fishing license is required for individuals 16 years and older who wish to collect grunion during the open season. Grunion may only be taken by hand; digging holes or using any tools, including nets, to entrap them is prohibited. The daily bag limit is 30 grunion per person.
There is also a closed season for grunion from April through June, during which observation is permitted, but taking fish is not allowed. This closed period aligns with their peak spawning time, ensuring the species’ continued health. Adhering to these regulations and leaving the beach undisturbed helps preserve this unique natural spectacle for future generations.