Grunion
Grunion Temporal range: Pleistocene to Present[1]
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California grunion , Leuresthes tenuis
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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]
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Grunion are two fish species of the
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.
Species
The currently recognized species in this genus are:[3]
- Leuresthes sardina (O. P. Jenkins & Evermann, 1889) (Gulf grunion)
- Leuresthes tenuis (Ayres, 1860) (California grunion)
Taxonomy
Grunion were originally classified as part of the Old World silverside family,
Distribution
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.
Appearance and growth
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
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.
Breeding
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
Feeding
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.
Threats
The reduction of spawning habitat due to
Status of population
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.
Fishing
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.
History
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]
References
- ^ Sepkoski, Jack (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on 2011-07-23. Retrieved 2007-12-25.
- ^ Eschmeyer, William N.; Fricke, Ron & van der Laan, Richard (eds.). "Leuresthes". Catalog of Fishes. California Academy of Sciences. Retrieved 20 June 2019.
- ^ Froese, Rainer and Pauly, Daniel, eds. (2012). Species of Leuresthes in FishBase. June 2012 version.
- ^ a b Roland, T. (9 April 2010). "Running with the Grunion". The Independent. Retrieved 20 August 2016.
- ISBN 978-1482207972.
- ^ "California Department of Fish & Game, Marine Region". California Department of Fish & Game. Retrieved 2008-03-24.
- ^ Ayres, Proc. Calif. Acad. Sci. (Ser. 1) v. 2)
Further reading
- Gregory, Paul A. (December 2001). California's Marine Living Resources: A Status Report – Grunion. California Department of Fish and Game.
External links
- grunion.org
- The Amazing Grunion Archived 2013-03-06 at the Wayback Machine (California Dept. of Fish & Game)
- Grunion Greeters (volunteer observers)
- The Cabrillo Museum Grunion Programs in San Pedro, California
- Does Beach Grooming Harm Grunion Eggs?
- Fishbase Leuresthes tenuis (Ayres 1860) California grunion
- Fishbase Leuresthes sardina (Jenkins & Evermann 1889) Gulf grunion
- Fishbase Colpichthys regis (Jenkins & Evermann, 1889) False grunion
- Decoding the Grunion's Ways - LA Times article