''Leuresthes tenuis'', the California grunion, is a species of

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

native to the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

coast of

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

from

Monterey Bay Monterey Bay is a bay of the Pacific Ocean located on the coast of the U.S. state of California, south of the San Francisco Bay Area. San Francisco itself is further north along the coast, by about 75 miles (120 km), accessible via California S ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

. This species grows to in

total length Fish measurement is the measuring of individual fish and various parts of their anatomies, for data used in many areas of ichthyology, including taxonomy and fishery biology. Overall length Standard length (SL) is the length of a fish measured f ...

and is of minor importance to local fisheries, particularly during grunion runs in which the fish beach themselves to lay their eggs and are easily taken.

Description

The California grunion is a long, slender fish with a deeply forked tail. The dorsal fin is in two parts and has five to seven spines and nine to ten soft rays. The origin of the anal fin is immediately below the first dorsal fin, and this fin has twenty-one to twenty-four soft rays. The fish grows to a maximum length of . It is greenish above and silvery below. There is a blue patch on the cheek and a silvery-blue lateral stripe along the side.

Distribution

This species is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to the eastern Pacific Ocean. Its range extends from Monterey Bay southwards to Baja California, but it is uncommon north of

Point Conception Point Conception (Chumashan languages, Chumash: ''Humqaq'') is a headland along the Gaviota Coast in southwestern Santa Barbara County, California, United States. It is the point where the Santa Barbara Channel meets the Pacific Ocean, and as ...

. It is also found in the

Gulf of California The Gulf of California (), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Vermejo''), is a marginal sea of the Pacific Ocean that separates the Baja California peninsula from ...

. Its depth range is from the sea surface down to about .

Breeding

Breeding takes place between about March and August and happens on the second, third and fourth nights following the full moon, a little while after the tide has peaked. The fish swim towards a sandy beach and are carried up the shore by the advancing waves. Each female then digs herself into the sand tail first and lays a clutch of eggs in the wet sand. Several males may attempt to mate with one female, curling around her while they shed their

milt Milt is the seminal fluid of fish, mollusks, and certain other water-dwelling animals. They reproduce by spraying this fluid which contains the sperm, onto roe (fish eggs). It can also refer to the sperm sacs or testes that contain the semen. ...

, after which they get washed back to the sea. The female finishes laying her eggs, emerges from the sand and moves down the beach, the whole process usually taking half minute or so. The eggs remain buried in the sand until the next series of

spring tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables c ...

following the

new moon In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar eclipse. ...

a fortnight later. In the laboratory it has been shown that the eggs develop and are ready to hatch after about ten days, but only actually hatch after a period of agitation, as might occur when waves were pounding the sand in which they were buried and scouring away the sand covering them. By the time this happens in the wild, a fortnight after the eggs were laid, the female fish will have another batch of mature eggs, and may deposit these eggs in a similar manner at night during the exceptionally high tides associated with the new moon. Although some other fish species leave their eggs in locations that dry out (a few, such as

plainfin midshipman The plainfin midshipman (''Porichthys notatus'') is a species of bottom-dwelling Batrachoididae, batrachoid toadfish. It is a member of the midshipman fish, midshipman genus, ''Porichthys'', the only batrachoid fishes that have photophores. It is ...

, may even remain on land with the eggs during low tide) or on plants above the water ( splash tetras), jumping onto land ''

en masse Many words in the English vocabulary are of French origin, most coming from the Anglo-Norman spoken by the upper classes in England for several hundred years after the Norman Conquest, before the language settled into what became Modern Eng ...

'' to spawn is unique to the two

grunion Grunion are two fish species of the genus ''Leuresthes'': the California grunion, ''L. tenuis'', and the Gulf grunion, ''L. sardina''. They are sardine-sized teleost fishes of the New World silverside family Atherinopsidae, found only off th ...

capelin The capelin or caplin (''Mallotus villosus'') is a small forage fish of the smelt family found in the North Atlantic, North Pacific and Arctic oceans. In summer, it grazes on dense swarms of plankton at the edge of the ice shelf. Larger capel ...

and

grass puffer The grass puffer (''Takifugu niphobles''), or Kusa-fugu (), is a species of fish in the pufferfish family (Tetraodontidae). This common to abundant species is found in the northwest Pacific Ocean in China (including Hong Kong and Taiwan), Japan, ...

.Martin, K.L.M. (2014). Beach-Spawning Fishes: Reproduction in an Endangered Ecosystem. CRC Press. .

Feeding

The fish feed on plankton such as

copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...

s. They are preyed on by

California halibut The California halibut or California flounder (''Paralichthys californicus'') is a large-tooth flounder native to the waters of the Pacific Coast of North America from the Quillayute River in Washington (U.S. state), Washington to Magdalena Bay ...

rock bass The rock bass (''Ambloplites rupestris''), also known as the rock perch, goggle-eye, red eye, and black perch, is a freshwater fish native to east-central North America. This red-eyed fish is a species of freshwater fish in the sunfish family (bi ...

white croaker White croaker (''Genyonemus lineatus'') is a species of croaker occurring in the Eastern Pacific. White croakers have been taken from Magdalena Bay, Baja California Sur, to Vancouver Island, British Columbia, but are not abundant north of San Fra ...

s and other large predators. Humans catch them for culinary use or use them as bait. The eggs are at risk from shore birds such as the whimbrel and the

marbled godwit The marbled godwit (''Limosa fedoa'') is a large migratory shorebird in the family Scolopacidae. On average, it is the largest of the four species of godwit. Taxonomy In 1750 the English naturalist George Edwards included an illustration and a ...

, which probe the sand with their beaks. The eggs are also sought by sandworms,

ground squirrel Ground squirrels are rodents of the squirrel family (Sciuridae) that generally live on the ground or in burrows, rather than in trees like the tree squirrels. The term is most often used for the medium-sized ground squirrels, as the larger ones ar ...

s, a species of

isopod Isopoda is an Order (biology), order of crustaceans. Members of this group are called isopods and include both Aquatic animal, aquatic species and Terrestrial animal, terrestrial species such as woodlice. All have rigid, segmented exoskeletons ...

, and certain beetles and flies.

References

{{Taxonbar, from=Q1817767 Atherinopsidae Fish described in 1860 Fish of the Pacific Ocean Fish of North America Taxa named by William Orville Ayres