The allis shad (''Alosa alosa'') is a widespread Northeast Atlantic species of

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

in the herring family, Clupeidae. It is an

anadromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousan ...

fish which migrates into fresh water to spawn. It is found in the eastern Atlantic Ocean, the western Baltic Sea and the western Mediterranean Sea. In appearance it resembles an

Atlantic herring Atlantic herring (''Clupea harengus'') is a herring in the family (biology), family Clupeidae. It is one of the most abundant fish species in the world. Atlantic herrings can be found on both sides of the Atlantic Ocean, congregating in large ...

but has a distinctive dark spot behind the gill cover and sometimes a row of up to six spots behind this. It sometimes hybridises with the

twait shad The twait shad or twaite shad (''Alosa fallax'') is a species of fish in the family Clupeidae. It is found in the eastern Atlantic Ocean and the Mediterranean Sea and is an anadromous fish which lives in the sea but migrates into fresh water to s ...

(''A. fallax''). This fish becomes mature when three or more years old and migrates to estuaries, later swimming up rivers to spawn. Populations of this fish have declined due to

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in th ...

, pollution and

habitat destruction Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...

. Conservation of this species is covered by Appendix III of the Bern Convention and Appendix II and V of the

European Community Habitats Directive The Habitats Directive (more formally known as Council Directive 92/43/EEC on the Conservation of natural habitats and of wild fauna and flora) is a directive adopted by the European Community in 1992 as a response to the Berne Convention. The E ...

Description

The allis shad is a typical herring-type fish. It has no

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial ...

and a somewhat rounded belly. The gill cover is ridged and the

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number w ...

large. The back is a bluish-green colour and the head brownish with a golden tinge on the operculum. The flanks are silvery, sometimes with a bronzy tinge, and a distinctive large dark spot occurs just behind the gill cover, and occasionally one to six smaller spots behind that. The adult length is typically .

Distribution

The allis shad is found in the eastern Atlantic in waters bordering most of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

and northwestern

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

, and it enters to the western

Baltic Baltic may refer to: Peoples and languages * Baltic languages, a subfamily of Indo-European languages, including Lithuanian, Latvian and extinct Old Prussian *Balts (or Baltic peoples), ethnic groups speaking the Baltic languages and/or originati ...

and western

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...

Seas, but it is rare outside

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

Biology and lifecycle

''Alosa alosa'' has a similar lifecycle to that of the

''A. fallax''. They are known to live in

sympatry In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...

,Lochet, A., S. Boutry, and E. Rochard. ''Estuarine Phase during Seaward Migration for Allis Shad Alosa Alosa and Twaite Shad Alosa Fallax Future Spawners.'' Ecology of Freshwater Fish 18 (2009): 323-35. and the two species can hybridize. They are

species like many other species in the genus ''Alosa''.Coscia, I., V. Rountree, J. J. King, W. K. Roche, and S. Mariani. ''A Highly Permeable Species Boundary between Two Anadromous Fishes.'' Journal of Fish Biology 77.5 (2010): 1137-149. However, some record of them being landlocked suggests an ability to adapt well to their environment. They primarily live at sea on feeding grounds and migrate to their spawning grounds between April and June once they are sexually mature. Maturity usually ranges from 3–7 years of age. ''A. alosa'' can usually only reproduce once in their lifetimes. Juveniles appear in

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

and brackish water around July to August. The salinity of brackish water may pose problems to the juveniles migrating from fresh water.

Population reduction

Populations have been reduced primarily by overfishing, pollution, and habitat destruction. The estuarine phase, or the time that they are in the estuaries migrating from spawning grounds to sea, is estimated to have a duration in ''A. alosa'' of up to six months. The estimate, however, does not take into account individual variation and/or survival of juveniles in the estuarine phase.

Conservation

Four special areas of conservation have been designated in Ireland where ''Alosa'' species have been known to spawn. ''Alosa alosa'' "has been placed in Appendix III of the Bern Convention (1979) that lists protected fauna species as well as in Appendix II and V of the European Community Habitats Directive (1992) that list, respectively, species whose conservation requires the designation of special areas of conservation and that are subject to management measures." However, ''A. alosa'' is currently under a moratorium (2008) in numerous French watersheds.

References

External links

*
EU LIFE-Project: The re-introduction of allis shad (''Alosa alosa'') in the Rhine system
* {{Authority control allis shad Fauna of France Marine fish of Europe allis shad allis shad Least concern biota of Europe Taxonomy articles created by Polbot