California grunion are small, silvery fish known for a unique spawning ritual. These slender marine creatures come entirely out of the ocean onto sandy beaches to reproduce. This remarkable behavior occurs predictably along their coastal habitats.
Understanding Grunion
California grunion ( Leuresthes tenuis ) are slender, silvery fish, typically measuring five to seven inches long. They possess large eyes and primarily feed on tiny crustaceans and zooplankton. Grunion have a relatively short lifespan, generally living for about three to four years.
They inhabit nearshore coastal waters and bays, remaining in shallow areas near the surface. Their natural habitat extends along the Pacific coast, predominantly from Point Conception in California south to Punta Abreojos in Baja California, Mexico.
The Grunion Run Phenomenon
Grunion are renowned for their unique spawning behavior, known as a “grunion run,” where they intentionally leave the water to reproduce on sandy beaches. This occurs from late February or early March through August or early September. This unusual method helps protect their eggs from marine predators. The runs are precisely timed, taking place on the nights of the highest tides, typically following a new or full moon.
Spawning runs usually occur on the second, third, fourth, and fifth nights after the new or full moon, with the third and fourth nights often being the most active. The process unfolds after the high tide has begun to recede, ensuring eggs are deposited high enough on the beach to remain undisturbed. A female grunion rides a wave onto the sand, then burrows herself tail-first into the wet sand to create a nest. While she is partially buried, one or more male grunion will curve around her to fertilize the eggs she deposits.
After laying eggs, both male and female grunion return to the sea on the next receding wave. The eggs remain buried in the sand for approximately 10 days. Their hatching is triggered by the mechanical action of waves from the next series of high tides, releasing the larvae into the ocean. Females can spawn multiple times, up to six times in a season, with each event occurring approximately every two weeks.
How to Observe Grunion Runs
Observing a grunion run can be a memorable experience, typically occurring from March through August. Peak spawning activity generally takes place between late March and early June. Runs can occur along many sandy beaches from San Diego to Santa Barbara, with Orange and Los Angeles counties often experiencing frequent activity.
To enhance your viewing experience, plan to arrive about an hour before the predicted run time, as fish may appear earlier or later. Bring warm clothing, a blanket or chair, and a flashlight, preferably with a red filter, as bright white lights can startle the fish. When grunion appear, minimize light and noise, giving the fish ample space to complete their spawning ritual. Avoid shining lights directly on the water or the fish to prevent disturbing them.
Protecting Grunion and Their Habitat
Protecting grunion and their sandy beach habitats is important for the species’ existence. Grunion eggs, buried in the sand, are vulnerable to disturbances from human activities like recreational beach use, vehicle traffic, and beach grooming. Coastal development, erosion, and pollution also contribute to habitat loss, directly impacting grunion populations.
To help conserve grunion, specific regulations are in place for their recreational take in California. A California sport fishing license is required for individuals 16 years and older who wish to collect grunion during the open season. Grunion may only be collected by hand; nets, traps, or digging holes to entrap them are prohibited. A daily bag and possession limit of 30 grunion per person is also in effect.
The grunion spawning season has a designated closed period from April 1 through June 30, during which no grunion may be taken or handled. During this closed season, observation is permitted, but touching or disturbing the fish is not allowed. Responsible viewing, which includes respecting regulations and minimizing disturbance, contributes to the long-term health of grunion populations.