Fish Have Sex on the Beach? Grunion's Quirky Mating Method Attracts a Crowd

Eric Wittman's flickr page/via

If you enjoy moonlit walks, then spring can be one of the happiest times of the year in southern California, especially if you are a grunion! California beaches are packed with people during the warm spring and summer days, but few people stick around to watch the fish that replace the sunbathers at night.

The California Grunion are small, silvery fish, related to smelt, with an unusual mating habit. The grunion "run" or spawn out of the water and on the sand. Grunion runs are timed with the tides. During some runs only a few fish come out of the water. But if you are lucky and pick a good night and location, then the sight of thousands of fish slithering in the moonlight is a magical experience that awaits you.

The Grunion’s Run and Range

The grunion can be found along Pacific beaches from Point Abreojos, Mexico, to Santa Barbara, California. The fish do not migrate, they carefully choose a beach to spawn on from March through August each year. The entire cycle is based on the tides. Grunions run on four consecutive nights when the tides are highest during new or full moons. Spawning occurs after high tide and continues for several hours.

A Marvelous Night for a Moondance

Usually a lone fish scout comes out to check if the coast is clear. If it is, the female begins the moondance spawning ritual by twisting and digging the bottom part of her body into the sand until she is half buried. She then deposits her eggs in her newly excavated cylinder, shaped hole. The male circles and wraps himself around the female, and then bodies entwined, fertilizes the eggs. As waves break on the beach, grunion swim as far up the slope as possible. After spawning, most of the adult fish make it back to the ocean.

Mature grunion may spawn during successive runs, with females spawning up to six times each season. Females can lay up to 3,600 eggs during one spawn. The eggs are kept moist by residual water in the sand. The lower tides that follow for several days after the run allow the eggs to develop, and the sand protects them. They hatch about nine days later, when the next high tide series washes over them, agitating them and causing them to hatch.

Grunion Hunting Season

If just watching the fish in wonder isn’t enough, you can also capture the fish during open season. Open season takes place during the months of March, June and July. All that is needed is a valid California fishing license if you are 16 years or older. The only catch is no gear or nets are allowed, you can’t even dig a hold to entrap them, so people catch the slimy, slithery fish with their bare hands and then place them in pails.

Despite the hunting, the grunion population seems to be maintained at a fairly constant level. The more critical issue is the loss of spawning habitat caused by beach erosion, harbor construction, and pollution. Beach construction, such as shoreline armoring, can eliminate grunion spawning grounds. Beach maintenance, such as the use of bulldozers or rakes to groom the sand can be deadly to grunion nests

Grunion Conservation Efforts

Grunion Greeters is a citizen monitoring group, made up of trained volunteers who stand on the beach during the first few months of the run season, observing the fish activities and recording them for NOAA records.

Recommended Beach Viewing Spots

Some of the best beaches to view the runs are: Will Rogers, Zuma, Mother's Beach, White's Point, Salt Creek, Crescent Bay, Doheny State Beach, San Clemente State Beach, and Newport Beach. Some locals insist the beach needs to be a south-facing beach. Others recommend a full moon instead of the new moon. If you go, let us know which worked best for you.

Grunion Led Tours

Cabrillo Marine Museum has an educational program approximately once a month during the season that begins at 9pm, followed by a guided observation at the beach. April 8th is their next scheduled program. Remaining dates for the season are: April 23, May 7, June 5, June 21 and July 20, 2012.

If you go with a guided tour or on your own, don’t forget warm clothing and a flashlight.

Tags: Beaches | California | Conservation | Fish

Best of TreeHugger