The grunion are running

 

Photo by Gary Florin, CMA

LONG BEACH,  California - Grunion are small, silver fish that live in the ocean off the coast of southern California and northern Baja California (a state in Mexico).  They swim in the sea and use their gills to breathe just as other fish do.  So why do crowds of people brave dark, chilly nights to see them?  Because unlike other fish, grunion come completely out of the water and onto land to reproduce. 

Between March and August, the grunion run ashore a few nights after the new and full moons, when high tides are higher than normal.  Usually between 10 p.m. and 1 a.m., high tide washes the fish onto several California beaches.  There, females dig their tails into the sand while males curl around them to fertilize the eggs the female fish are laying.  When the process is finished - in as little 30 seconds - they all catch the next wave back into the ocean. 

The eggs remain buried in the sand and incubate for 10 to 14 days until the next new- or full-moon high tide comes in and washes them out to sea.  The churning motion of the waves bursts the protective membrance of the eggs and the tiny fish are hatched. 

The Cabrillo Marine Aquarium in Long Beach and the Birch Aquarium in San Diego both offer public programs for viewing grunion.