Group greets grunion

By Will Parson

Birch Aquarium program fleshes out the biology of the silvery sand-spawning species

Dozens of adults and children learned the ways of the grunion on March 28 at the first of several events hosted by the Birch Aquarium at the Scripps Institution of Oceanography.

Attendees absorbed the intricacies of the small and gregarious fish species, famous for its late night spawning behavior, before heading down to Scripps Beach for the start of the grunion’s peak spawning season, which spans April and May.

The group got the chance to hatch their very own grunion larvae when volunteers passed out small cups containing eggs collected two weeks prior. After adding a little seawater and a shake of the wrist to simulate the rising tide that releases wild grunion eggs from sandy shores, families hunched over their cups to watch the larvae burst from their eggs in a motion that takes just a fraction of a second. Volunteers later led the group down to the beach to release their newly hatched grunion into the waves.

Karen Martin, a marine biologist at Pepperdine University and executive director of the statewide Grunion Greeters project, gave a special presentation to the group about the biology and conservation efforts concerning the California grunion, which is labeled a species of special concern by the California Department of Fish and Game. Martin stressed grunion awareness, explaining, “They don’t occur anywhere else and they are vulnerable to human activities.”

The California grunion, Leuresthes tenuis, is indigenous to the coast of southern California and northern Baja California, and San Diegans may notice an unkempt intertidal zone during their next visit to the beach, thanks to the species’ breeding habits. Beach managers leave seaweed and other natural detritus intact to safeguard the grunion eggs buried underneath the sand.

The largest runs can summon thousands of grunion onto the beach for up to an hour, but they were hard to find on Saturday. Beaches throughout San Diego that night saw few fish despite the predictions, and the group at Scripps saw just a few grunion scouts -individual fish that come ashore to sense the beach conditions before a run occurs. For one reason or another, the grunion simply decided not to show up.

SIO scientist Boyd Walker pioneered grunion research in the 1940s, and his studies are the basis for grunion run predictions. But the grunion can be elusive at times, and scientists like Martin still use reports on grunion run events for research efforts.

The need for data is partly the basis for the Grunion Greeters project, which invites everyday citizens to become grunion reporters after attending a small workshop. Martin, who appreciates the efforts of these volunteers, said, “The thing about the grunion greeters is that these are citizen scientists … people from all walks of life and they’re making a really big difference in the way these animals are treated and the way the beaches are being managed. And that’s a pretty cool thing.”