The California grunion (Leuresthes tenuis) is a small New World silverside fish (family Atherinopsidae) found only on the Southern California coast from Point Conception as far south as Punta Abreojos (about half-way down the Baja peninsula) although the majority of the population is thought to live in Los Angeles county, Orange County and San Diego county. The California grunion is well-known for its unique springtime spawning behavior that it accomplishes not in the water, but at extreme high tides on sandy beaches on nights just after the full moon and the new moon. During these times, the females ride waves up as far up the beach as they can, dig their tails into the sand, and wait for subsequent waves to bring males to them. Males (sometime multiple) wind their bodies around the female and spawn, releasing sperm that flow down the female’s body to fertilize the eggs she lays in the sand, about four inches under the surface. When the process is done, males and females return to the sea. The buried eggs incubate in the moist sand and usually hatch when agitated by the surf in the next high tide series. Grunion mature after one year, and live about three years, inhabiting local coastal waters up to 60 feet deep. Females spawn as many as six times each season, during which time they lay a total of about 18,000 eggs.

Although they seem abundant during spawning runs, scientists believe the population size of California grunion is quite restricted. Birds, fish and sea lions are among predators of grunion. However the biggest threat to grunion is human activity: pollution of waters, development of spawning grounds, beach grooming using tools that disrupt egg nests, and human harvesting, which disrupts spawning runs. Recreational fishing is allowed, by license, but only when grunion are caught by hand, without nets or other tools. The season is closed during peak spawning time, April-June, when grunion are most vulnerable.

The genus (Leuresthes) contains only one other species, the Baja grunion (L. sardinas), which lives only in the gulf of California where it carries out similar spawning behavior.

(California Department of Fish and Game 2012; grunion.org; Wikipedia 2011)

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: San Francisco, California, to Magdalena Bay, Baja California, but rare north of Point Conception in southern California.

Habitat Type: Marine

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

United States

Rounded National Status Rank: NNR - Unranked

Rounded Global Status Rank: GNR - Not Yet Ranked

Comments: Patterns of allozyme variation indicate a population structure that approximates panmixia but also suggests isolation by distance (Gaida et al. 2003).