Grunion Temporal range: Pleistocene to Present [1] | |
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California grunion, Leuresthes tenuis | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
Order: | Atheriniformes |
Family: | Atherinopsidae |
Subfamily: | Atherinopsinae |
Tribe: | Atherinopsini |
Genus: | Leuresthes D. S. Jordan & C. H. Gilbert, 1880 |
Type species | |
Atherinopsis tenuis Ayres, 1860 [2] |
Grunion are two fish species of the genus Leuresthes: the California grunion, L. tenuis, and the Gulf grunion, L. sardinas. They are sardine-sized teleost fishes of the New World silverside family Atherinopsidae, found only off the coast of California, USA, and Baja California, Mexico, where the species are found on both the Pacific Ocean and Gulf of California coasts. Many people enjoy catching grunion at events called "grunion runs."
Grunion are known for their unusual mating ritual wherein at very high tides, the females come up on to sandy beaches where they dig their tails into the sand to lay their eggs. The male then wraps himself around the female to deposit his sperm, and for the next 10 days the grunion eggs remain hidden in the sand. At the next set of high tides, the eggs hatch and the young grunion are washed out to sea.
A related species, the false grunion (Colpichthys regis) lives in the Gulf of California. Although the fish looks and acts similarly, it does not have the same breeding method.
The currently recognized species in this genus are: [3]
Grunion were originally classified as part of the Old World silverside family, Atherinidae, but are now classified in the family Atherinopsidae along with other New World silversides including the jacksmelt and topsmelt.
The California grunion, L. tenuis, is found along the Pacific Coast from Point Conception, California, to Punta Abreojos, Baja California Sur. They are rarely found between San Francisco in the north and San Juanico Bay, Baja California Sur, in the south. The Gulf grunion, L. sardina, is found along the coast of Baja California in the Gulf of California. Inhabiting the nearshore waters from the surf to a depth of 60 ft (18 m), marking experiments indicate they are not migratory.
They are small, slender fish with bluish-green backs and silvery sides and bellies. Their snouts are bluntly rounded and slippery. Silversides differ from true smelts of the family Osmeridae in that they lack the trout-like adipose fin.
Young grunion grow rapidly and are about five inches long by the time they reach one year old and are ready to spawn. Adult fish normally range in size from 6 to 7 in (15 to 18 cm) with a maximum recorded size of 8.5 in (220 mm) (San Diego, CA., 05-11-05).[ citation needed ]
Average body lengths for males and females are 4.5 and 5 in (11 and 13 cm), respectively, at the end of one year; 5.5 and 5.8 in (14 and 15 cm) at the end of two years; and 5.9 and 6.3 in (15 and 16 cm) at the end of three years.
The normal lifespan of the grunion is three to four years, although individuals up to five years old have been found. Their growth rate slows after the first spawning and stops completely during the spawning season. Consequently, adult fish grow only during the fall and winter. This growth rate variation causes annuli to form on the scales, which have been used for determining ages.
California grunion spawn on beaches from two to six nights after the full and new moon beginning soon after high tide and continuing for several hours. As a wave breaks on the beach, the grunion swim as far up the slope as possible. The female arches her body while keeping her head up and excavates the semifluid sand with her tail. As her tail sinks, the female twists her body and digs tail first until she is buried up to her pectoral fins. After the female is in the nest, up to eight males attempt to mate with her by curving around the female and releasing their milt as she deposits her eggs about four inches (10 cm) below the surface. After spawning, the males immediately retreat toward the ocean. The milt flows down the female’s body until it reaches the eggs and fertilizes them. The female twists free and returns to the sea with the next wave. The whole event can happen in 30 seconds, but some fish remain on the beach for several minutes. Spawning may continue from March through August, with occasional extensions into February and September. However, peak spawning is from late March through early June. Once mature, an individual may spawn during successive spawning periods at about 15-day intervals. Most females spawn about six times during the season. Counts of maturing ova to be laid at one spawning ranged from about 1,600 to about 3,600, with the larger females producing more eggs.[ citation needed ] A female might lay as many as 18,000 eggs over an entire season. The milt from the male might contain as many as one million sperm. Males may participate in several spawnings per run.
The eggs incubate a few inches deep in the sand above the level of subsequent waves. They are not immersed in seawater, but are kept moist by the residual water in the sand. While incubating, they are subject to predation by shore birds and sand-dwelling invertebrates. Under normal conditions, they do not have an opportunity to hatch until the next tide series high enough reaches them 10 or more days later. Grunion eggs can extend incubation and delay hatching if tides do not reach them for an additional four weeks after this initial hatching time. Most of the eggs will hatch in 10 days if provided with seawater and the agitation of the rising surf. The mechanical action of the waves is the environmental trigger for hatching. The rapidity of hatching, which occurs in less than one minute, indicates it is probably not an enzymatic function of a softening of the chorion as in some other fishes.
The Gulf grunion, with its smaller eggs, is unique in that it spawns during both night and daytime. [4]
Although some other fish species leave their eggs in locations that dry out (a few, such as plainfin midshipman, may even remain on land with the eggs during low tide) or on plants above the water (splash tetras), jumping onto land en masse to spawn is unique to the grunion, capelin and grass puffer. [4] [5]
Grunion feeding habits are not well known. They have no teeth and feed on very small organisms such as plankton. In a laboratory setting, grunion eat live brine shrimp.
The reduction of spawning habitat due to beach erosion, harbor construction, and pollution is believed to be the most critical problem facing the grunion species.[ citation needed ] An isopod, two species of flies, sandworms, and a beetle have been found preying on the eggs. Some shorebirds such as egrets and herons prey on grunion when the fish are on shore during spawning. Seagulls, sea lions, and larger fish such as sand sharks have also been observed feeding on grunion during a grunion run.
Despite local concentrations, the grunion is not an abundant species. While the population size is not known, all research points to a restricted resource that is adequately maintained at current harvest rates under existing regulations.
In the 1920s, recreational fishing of grunion caused definite signs of depletion resulting in a regulation passed in 1927 that established a closed season of three months from April until June. Grunion stocks improved and in 1947 the closed season was shortened to the months of April and May. This closure is still in effect to protect grunion during their peak spawning period.
The periodic appearance of the grunion on Southern California beaches, and the act of catching them, is locally known as a "grunion run". A fishing license is required for persons 16 years and older to catch grunion, and they may be taken by sport fishermen using their hands only. No appliances of any kind may be used to catch grunion, and no holes may be dug in the beach to entrap them. Grunion may be taken on specified dates between March and the end of August, but not during the months of April and May. There is no limit, but fishermen may take only what they can use, as under Californian law it is unlawful to waste fish. [6] With these regulations, the resource seems to be maintaining itself at a fairly constant level.
The coastal Native Americans in California harvested grunion during spawning runs. Archeologists have found fossil grunion otoliths (tiny, bonelike particles or stony platelike structures in the internal ear of lower vertebrates) at various Native American campsites.
Grunion were mentioned by Spanish explorer Juan Rodríguez Cabrillo in his ship's log dated around 1542.
Scientists first identified grunion in San Francisco Bay in 1860. [7]
Triggerfish are about 40 species of often brightly colored fish of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacific. Most are found in relatively shallow, coastal habitats, especially at coral reefs, but a few, such as the oceanic triggerfish, are pelagic. While several species from this family are popular in the marine aquarium trade, they are often notoriously ill-tempered.
The Atheriniformes, also known as the silversides, are an order of ray-finned fishes that includes the Old World silversides and several less-familiar families, including the unusual Phallostethidae. The order includes at least 354 species. They are found worldwide in tropical and temperate marine and freshwater environments.
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The American oystercatcher, occasionally called the American pied oystercatcher, is a member of family Haematopodidae. Originally called the "sea pie", it was renamed in 1731 when naturalist Mark Catesby observed the bird eating oysters. The current population of American oystercatchers is estimated to be 43,000. There are estimated to be 1,500 breeding pairs along the Atlantic and Gulf Coasts of the US. The bird is marked by its black and white body and a long, thick orange beak.
The inland silverside is a neotropical silverside native to eastern North America, and introduced into California. It is a fish of estuaries and freshwater environments.
The yellowbelly flounder is a flatfish of the genus Rhombosolea, found around New Zealand. A different species from the genus Rhombosolea is found in Australia and also goes by the name yellow-belly flounder. The Māori people have commonly fished for R. leporina, and many other species of flatfish, throughout New Zealand's coastal waters for hundreds of years. The Māori name for this species is pātiki tōtara.
The dwarf corydoras, dwarf catfish, tail spot pygmy catfish, or micro catfish is a tropical freshwater fish belonging to the subfamily Corydoradinae of the family Callichthyidae. It originates in inland waters in South America, and is found in the Amazon River and Paraguay River basins in Argentina, Bolivia, and Brazil. The specific epithet hastatus means with a spear, in reference to the spearhead-like spot on the tail root.
Chirostoma is a genus of Neotropical silversides from the Lerma River basin in Mexico, including lakes Chapala and Pátzcuaro. Fish in the genus collectively go by the common name charal/charales in their native range. They are heavily fished, but several of the species have become threatened due to habitat loss, introduced species and overfishing. Three species are considered extinct: C. bartoni, C. charari (1957) and C. compressum (1900). Four others have not been recorded recently and may also be extinct.
The Gulf grouper is a species of marine ray-finned fish, a grouper from the subfamily Epinephelinae which is part of the family Serranidae, which also includes the anthias and sea basses. It is endemic to Mexico.
The topsmelt silverside, also known as the topsmelt, is a species of Neotropical silverside native to the eastern Pacific Ocean.
The yellowfin whiting, also known as the western sand whiting or fine-scaled whiting, is a species of inshore marine fish in the smelt-whiting family Sillaginidae. The species is endemic to the eastern Indian Ocean, ranging from Dampier, Western Australia to Gulf St Vincent in South Australia, with an apparent division in the populations of the two states. Yellowfin whiting inhabit relatively shallow waters for their entire life, often found on tidal flats and creeks, as well as large estuaries. It is one of the largest members of the smelt-whiting family, growing to 42 cm, and can be distinguished by a number of anatomical and colour related features. Yellowfin whiting are benthic carnivores, preying predominantly on polychaete worms, with minor amounts of copepods, amphipods and bivalves also commonly taken. The species shows a change in diet with age, and also dietary differences with other sillaginids presumably to minimize competition. Reproduction occurs at different times throughout its range, generally focused around summer, with up to 217,000 eggs produced per season. Yellowfin whiting reach sexual maturity at around 20 cm, with each individual spawning more than once. The species forms the basis of major fisheries in both Shark Bay, Western Australia and the two Gulfs of South Australia, with around 260 tonnes of fish taken each year. They are also a popular target for shore based anglers, with a reputation as a very good table fish.
Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, to spawn refers to the process of freely releasing eggs and sperm into a body of water ; the physical act is known as spawning. The vast majority of aquatic and amphibious animals reproduce through spawning. These include the following groups:
Night smelt is a true smelt of the family Osmeridae. It is native to the Pacific coast of North America.
Sphyraena argentea is a predatory species of marine barracuda fish of the family Sphyraenidae. They are found in the northeast Pacific Ocean, from Cabo San Lucas, Baja California Sur north to Washington State. However, they are not common north of Point Conception in Santa Barbara County, California, usually preferring warmer waters. They can reach a length of about 1.2 metres (3.9 ft) and a weight of about 6.8 kilograms (15 lb). This species of barracuda is a very popular sport fish in Southern California.
Colpichthys is a genus of Neotropical silverside endemic to the Gulf of California.
Leuresthes tenuis, the California grunion, is a species of ray-finned fish native to the Pacific coast of North America from Monterey Bay in California to Baja California. This species grows to 19 cm (7 in) in total length 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.
Membras martinica, the rough silverside, is a species of Neotropical silverside from the family Atherinopsidae, it is the type species of the genus Membras.
The woolly sculpin is a species of ray-finned marine fish belonging to the family Cottidae, or the typical sculpins. It is found in the eastern Pacific Ocean, where it occurs along the coastline of California south to Baja California.
Odontesthes bonariensis is a species of Neotropical silverside, an euryhaline fish native to fresh, brackish and salt water in south-central and southeastern South America, but also introduced elsewhere. It is often known by the common name Argentinian silverside or pejerrey, but it is not the only species of silverside in Argentina and pejerrey is also used for many other silversides. It is a commercially important species and the target of major fisheries.
Leuresthes sardina, commonly known as Gulf grunion, is a species of grunion endemic to the Gulf of California. It is classified as Near Threatened by the IUCN.