This Shore Thing Isn’t Always a Sure Thing
Many Turn Out to Watch Grunion Fish Spawn on La Jolla Beaches

Shannon Casey | April 14, 2008

An adventurous crowd of kids and adults stayed up well past their bed time April 7 in hopes of witnessing a late-night, ocean wonder — the mysterious grunion run.

One of the Grunion Run participants points to the spawning fish.

The night marked the 2008 season launch of Birch Aquarium at Scripps’s naturalist-guided grunion runs, and the grunion — and humans — were out in full force. The participants were there to learn more about the unusual mating habits of the small, silvery fish and to try to catch a first-hand glimpse of a grunion run in action.

During this unique mating ritual, female grunion bury themselves in the sand and deposit up to 3,000 eggs each, while males protectively wrap themselves around the females to fertilize their eggs. When the dance is complete, both flip and flop their way back to the water where they can ride a wave back to sea.

The grunion can be picky about where they spawn, and sometimes choose not to appear on nights that would otherwise seem perfect for the fish, said naturalist Chelsea Rochman. The nights when grunion runs are most probable follow the highest tide after new and full moons along dark, sandy beaches in Northern Baja California and Southern California.

Last week, the Birch Aquarium’s program began with a presentation about grunion spawning behavior, during which participants watched grunion eggs in tiny cups of sand and saltwater hatch right before their eyes.

Following the presentation, dozens of hopeful, flashlight-clad grunion watchers anxiously wound their way through the darkened Scripps Institution of Oceanography campus to the beach below to experience the run. The nocturnal spawners didn’t disappoint; the observers arrived just after 11 p.m. to a shoreline glittering with hundreds of tiny fish.  Many said it was an incredibly exciting and beautiful natural phenomenon well worth a little lost beauty sleep.

Birch Aquarium at Scripps will be hosting additional late-night grunion lectures and beach excursions April 21, May 6, May 21 and June 4. The cost is $12 for adults and $9 for children ages 6 to 13. Reservations are required. Please call (858) 534-7336 for more details, or visit http://aquarium.ucsd.edu