California Grunion
Leuresthes tenuis

 

Physical Description

  • Small, slender fish, about 5 to 6 inches long.
  • Pearlescent blue-green backs, silver sides and bellies, and forked tails.
  • Large black eyes and no teeth.

Range

  • The coasts of California, and Baja California, Mexico.

Habitat

  • Inhabit nearshore waters, from surf zone to a depth of 60 feet.

Reproduction

  • Grunion are perhaps most famous for their Grunion Runs, their spawning events every spring and summer.
  • From March to September, but especially March to early June, hundreds of grunion ride waves out of the water and gather on the beach to spawn in the sand. This happens for the four days after each full moon and new moon.
  • The grunion leave the water right after high tide and stay out of the water for 1-3 hours.
  • Just a few fish (usually males), ride the waves in and strand themselves on the beach, and then hundreds follow.
  • A female drills herself into the sand as the waves go out, burying herself up to her pectoral fins, head up. The male curves around her on top of the sand.
  • Females deposit eggs  2-3 inches underneath the sand, and males fertilize them. Then both fish head back to the ocean.
  • Larger fish can produce up to 3000 eggs every two weeks.

Diet

  • Small zooplankton.
  • Not filter-feeders; use large eyes to hunt individual plankton prey rather than filter large amounts of water.

Predators

  • Halibut, corbina, guitarfish, seals, sea lions, sharks, dolphins, and squid feed on grunion in the water.
  • Herons, egrets, and other seabirds eat spawning grunion while they are on shore.

Interesting Facts

  • After the Grunion Run, the eggs are left buried in the sand, out of the water, for approximately two weeks. At the next very high tide of a new moon or full moon, the larvae hatch and re-enter the ocean.
  • During some months of the Grunion Runs, grunion can be recreationally fished, but only by hand! No gear allowed.
  • The name grunion came from early Spanish settlers; it is Spanish for “grunter” because of the squeaking noise they make while spawning.

Sources: CaliforniaBeaches.com; Oceana; Grunion.org; California Dept. of Fish and Wildlife

Photo: Matthew Meier 

Want to watch the grunion run in person? Find the best Grunion Run beaches and dates near you: https://www.californiabeaches.com/grunion-run-schedule/