Allis shad

{{Short description|Species of fish}} {{Speciesbox | name = Allis shad | image = Alosa alosa.jpg | status = CR | status_system = IUCN3.1 | status_ref =<ref name="iucn">{{cite iucn |author=Ford, M. |year=2024 |title=''Alosa alosa'' |article-number=e.T903A15541267 |doi=10.2305/IUCN.UK.2024-2.RLTS.T903A15541267.en}}</ref> | genus = Alosa | species = alosa | authority = (Linnaeus, 1758) |synonyms=*''Alausa vulgaris'' Valenciennes, 1847 *''Alosa communis'' Yarrell, 1836 *''Alosa cuvierii'' Malm, 1877 *''Alosa rusa'' Mauduyt, 1848 *''Clupea alosa'' Linnaeus, 1758 |synonyms_ref=<ref name="iucn"/><ref>{{GBIF|taxon=''Alosa alosa'' (Linnaeus, 1758)|id=2412685|access-date=29 October 2024}}</ref><ref name=FB>{{FishBase|Alosa|alosa|month=October|year=2024}}</ref> }} thumb|Allis shad

The '''allis shad''' ('''''Alosa alosa''''') is a widespread Northeast Atlantic species of fish in the Alosidae family. It is an anadromous fish which migrates into fresh water to spawn.<ref name="iucn"/><ref name=FB/> It is found in the eastern Atlantic Ocean, the western Baltic Sea and the western Mediterranean Sea. In appearance it resembles an Atlantic herring 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 (''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, pollution and habitat destruction. Conservation of this species is covered by Appendix III of the Bern Convention and Appendix II and V of the European Community Habitats Directive.

==Description== The allis shad is a typical herring-type fish. It has no lateral line and a somewhat rounded belly. The gill cover is ridged and the scales 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 {{convert|30|to|60|cm|abbr=on}}.<ref name=FB/><ref>{{cite web |url=http://www.luontoportti.com/suomi/en/kalat/allis-shad |title=Allis shad: ''Alosa alosa'' |publisher=NatureGate |access-date=14 December 2013}}</ref>

==Distribution== The allis shad is found in the eastern Atlantic in waters bordering most of Europe and northwestern Africa, and it enters to the western Baltic and western Mediterranean Seas, but it is rare outside and increasingly within France.<ref name="iucn"/><ref name=FB/> There are no longer breeding populations in Morocco or Mediterranean Spain.<ref name="iucn"/>

==Biology and lifecycle== thumb|left|Biology and lifecycle of ''Alosa alosa''. ''Alosa alosa'' has a similar lifecycle to that of the twait shad ''A. fallax''. They are known to live in sympatry,<ref name="Lochet">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.</ref> and the two species can hybridize.<ref name=Coscia/> They are anadromous species like many other species in the genus ''Alosa''.<ref name="Coscia">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 {{doi|10.1111/j.1095-8649.2010.02768.x}} 77.5 (2010): 1137–149.</ref> However, some record of them being landlocked suggests an ability to adapt well to their environment.<ref name=Coscia/> They primarily live at sea on feeding grounds and migrate to their spawning grounds between April and June once they are sexually mature.<ref name=Coscia/> Maturity usually ranges from 3–7 years of age.<ref name=Coscia/> ''A. alosa'' can usually only reproduce once in their lifetimes.<ref name=Coscia/> Juveniles appear in estuaries and brackish water around July to August.<ref name=Lochet/> The salinity of brackish water may pose problems to the juveniles migrating from fresh water.<ref name=Lochet/>

The estuarine phase, or the time spent in estuaries migrating from spawning grounds to sea, is estimated to have a duration in ''A. alosa'' of up to six months.<ref name=Lochet/> The estimate, however, does not take into account individual variation and/or survival of juveniles in the estuarine phase.<ref name=Lochet/>

==Population reduction== Populations have been reduced primarily by overfishing, pollution, and habitat destruction.<ref name=Coscia/> Siltation and gravel mining threaten spawning locations.<ref name="iucn"/> There is concern that barriers to migration like dams are causing allis shad to spawn downstream from their usual locations, potentially prompting hybridization with twaite shad.<ref name="iucn"/> Climate change may force the species' distribution to shift or contract further.<ref name="iucn"/> The International Union for Conservation of Nature listed the species as critically endangered in 2024, citing an estimated global population decline of around 80% over the past 20 years, leaving many small relict subpopulations and extirpating others.<ref name="iucn"/>

==Conservation== Four special areas of conservation have been designated in Ireland where ''Alosa'' species have been known to spawn.<ref name=Coscia/> ''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."<ref name=Lochet/> However, ''A. alosa'' is currently under a moratorium (2008) in numerous French watersheds.<ref name=Lochet/>

==References== {{Reflist}}

==External links== * [http://www.alosa-alosa.eu EU LIFE-Project: The re-introduction of allis shad (''Alosa alosa'') in the Rhine system] * {{Cite NIE|wstitle=Allice|year=1905 |short=x}}

Category:Alosa Category:Fauna of France Category:Marine fish of Europe Category:Fish described in 1758 Category:Animal taxa named by Carl Linnaeus Category:Least concern biota of Europe Category:Taxonomy articles created by Polbot Category:Habitats Directive species