Alosa

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Alosa<ref>{{#if:161701 | {{#invoke:template wrapper|wrap|_template=cite web|_exclude=id,ID,taxon 

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| Template:Citation error }}</ref> is a genus of fish, the river herrings, in the family Alosidae. Along with other genera in the subfamily Alosinae, they are generally known as shads.<ref>{{#if:551155 | {{#invoke:template wrapper|wrap|_template=cite web|_exclude=id,ID,taxon 

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| Template:Citation error }}</ref><ref name="Whitehead 1985">Template:Cite book</ref> They are distinct from other herrings by having a deeper body and spawning in rivers. Several species can be found on both sides of the Atlantic Ocean and the Mediterranean Sea. Also, several taxa occur in the brackish-water Caspian Sea and the Black Sea basin.<ref name=Coad/> Many are found in fresh water during spawning and some are only found in landlocked fresh water.

Appearance

Alosa species are generally dark on the back and top of the head, with blue, violet, or greenish tints.<ref name=Coad/> Some can be identified as having a grey or green back.<ref name=Coad/> Spots are commonly found behind the head, and the fins may vary from species to species or individually.<ref name=Coad/> Most species of Alosa weigh Template:Convert or less, with A. pontica and A. fallax weighing up to 2 kg, and A. alosa can exceed 3–4 kg.<ref name=Coad/>

Biology

Shads are thought to be unique among the fishes in having evolved an ability to detect ultrasound (at frequencies above 20 kHz, which is the limit of human hearing).<ref name="Mann">Template:Cite journal</ref> This was first discovered by fisheries biologists studying a type of shad known as blueback herring, and was later verified in laboratory studies of hearing in American shad. This ability is thought to help them avoid dolphins that find prey using echolocation. Alosa species are generally pelagic.<ref name="Greek">Template:Cite journal</ref> They are mostly anadromous or semianadromous with the exception of strictly freshwater landlocked species.<ref name=Greek/> Alosa species are generally migratory and schooling fish.<ref name=Greek/> Males usually mature about a year before females; they spawn in the late spring to summer.<ref name="travis">Template:Cite thesis</ref><ref name="Bianco">Template:Cite journal</ref> Most individuals die shortly after spawning.<ref name=travis/><ref name=Bianco/> Alosa species seemingly can change readily to adapt to their environments, as species are found in a wide range of temperatures and waters.<ref name="Bianco"/>

Lifecycle and reproduction

As Alosa species are generally anadromous, they face various obstacles to survival.<ref name="Lochet">Template:Cite journal</ref> They may have to pass through numerous barriers and waters to get to either their spawning grounds or normal habitats (the sea in most cases).<ref name=Lochet/> Estuaries are a major factor in numerous Alosa species' migrations.<ref name=Lochet/> Estuaries can be highly variable and complex environments contributing to fluctuating biological interactions,<ref name=Lochet/> with shifts in osmolarity, food sources, predators, etc.<ref name=Lochet/> Since many adult Alosa species die after spawning, only the young generally migrate to the sea from the spawning grounds.<ref name=Lochet/> Duration of migration varies among fish, but can greatly affect survival.<ref name=Lochet/>

Reproduction varies by species.<ref name="Coad">Template:Cite journal</ref> Studies done on Alosa in Iranian waters have shown that spawning varies in time, place, and temperature of the waters they inhabit.<ref name=Coad/> Species are known to spawn as early as April or as late as August.<ref name=Coad/> Temperatures range from about 11 to 27 °C.<ref name=Coad/> Fecundity can range from 20,000 to 312,000 eggs.<ref name=Coad/> Eggs are pelagic.<ref name=Coad/> Geography and temperature are important environmental factors in egg and young-of-year development.<ref>Template:Cite journal</ref>

The lifespan of Alosa species can be up to 10 years, but this is generally uncommon, as many die after spawning.<ref name=Coad/>

Systematics

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The systematics and distribution of Alosa shads are complex. The genus inhabits a wide range of habitats, and many taxa are migratory. A few forms are landlocked, including one from Killarney in Ireland, two from lakes in northern Italy, and two in Greece. Several species are native to the Black and Caspian Seas. Alosa species of the Caspian are systemically characterized by the number of rakers on the first gill arch.<ref name="Malkin">Template:Cite journal</ref> They are classified as being "multirakered", "medium-rakered", or "oligorakered".<ref name=Malkin/> The multirakered are primarily plankton feeders, the oligorakered have large rakers and are predators, and the medium-rakered generally consume a mixed diet.<ref name=Malkin/> Most current species of the genus Alosa in North America can be found in Florida, whereas the distribution of most of them is broader.<ref name=McBride>Richard S. McBride (2000). Florida's Shad and River Herrings (Alosaspecies): A Review of Population and Fishery Characteristics. Florida MAR8INE Research Institute Technical Reports: Technical Report TR-5, Florida Fish and Wildlife Conservation Commission. St. Petersburg, Florida.</ref>

Morphology is notoriously liable to adapt to changing food availability in these fish. Several taxa seem to have evolved quite recently, making molecular analyses difficult. In addition, hybridization may be a factor in shad phylogeny.<ref name="Faria">Template:Cite journal</ref> Nonetheless, some trends are emerging. The North American species except the American shad A. sapidissima can probably be separated in a subgenus Pomolobus. Conversely, the proposed genus (or subgenus) Caspialosa for the Caspian Sea forms is rejected due to paraphyly.<ref name=Faria/>

Species by geographical origin

North America

Western Europe and the Mediterranean

Caspian Sea, Black Sea, the Balkans

Fossil species

File:Clupeidae - Alosa elongata.JPG
Fossil of Alosa elongata

The following fossil Alosa species are known. An especially high diversity of fossil Alosa species is known from a mid-late Miocene-aged deposit in Pınarhisar District, Turkey:<ref name=":0">Template:Cite journal</ref><ref name=":1">Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation

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|CitationClass=web }}</ref> Miocene of Turkey

The former fossil species A. ovalis Rückert-Ulkümen, 1965 is now placed in Clupeonella as Clupeonella ovalis.<ref name=":1" />

Recreational fishing

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Commercial fishing

Commercial capture production of wild shad in tonnes.<ref>FAO (2006) Yearbooks of Fishery Statistics Summary Tables</ref><ref>FAO (2014) Yearbook - Fishery and Aquaculture Statistics, no. 24.</ref>
1999 2000 2001 2002 2003 2004 2005 2008 2010 2011 2012 2013 2014
788,770 860,346 665,284 589,692 524,800 569,160 605,548 588,978 645,977 611,371 604,842 628,622 636,678

Management

Shad populations have been in decline for years due to spawning areas blocked by dams, habitat destruction, pollution, and overfishing. Management of shad has called for more conservative regulations, and policies to help the species have lower fishing mortality.<ref name="asmfc-shad">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Political significance

Shad serve a peculiar symbolic role in Virginia state politics. On the year of every gubernatorial election, would-be candidates, lobbyists, campaign workers, and reporters gather in the town of Wakefield, Virginia, for shad planking. American shad served as the focal point of John McPhee's book The Founding Fish.<ref>"American Shad - Fish Reference Library - RedOrbit." RedOrbit - Science, Space, Technology, Health News and Information. 3 Apr. 2007. Web. 27 Nov. 2011. <http://www.redorbit.com/education/reference_library/science_1/fish/2579052/american_shad/index.html>.</ref>

Culinary use

File:Shad roe.jpg
Shad roe

The roe, or more properly the entire engorged uterus of the American shad—filled with ripening eggs, sautéed in clarified butter and garnished with parsley and a slice of lemon—is considered a great delicacy, and commands high prices when available.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

See also

References

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