Overview

Comprehensive Description

Biology

Amphihaline species (Ref. 51442), schooling and strongly migratory (Ref. 188). Adults are usually found in open waters along the coast (Refs. 59043, 89486); juveniles are usually found along estuaries and near the shore (Ref. 59043), possibly making vertical diurnal movements synchronized with the tides; they remain in estuaries for over one year (Ref. 89630). Migrates to major rivers to spawn; also reported to spawn in small rivers. Several landlocked (lake) non-migratory populations exist (Ref. 10541). Ichthyophagous, feeds on small fishes and crustaceans, the young taking the fry of herrings, sprats and gobies (Ref. 188, Ref. 51442). Females grow faster and are always larger than males of the same age (Ref. 10541). Very locally distributed due to pollution and impoundment of large rivers throughout Europe and most populations declined during the first decade of the 20th century, but seem to have stabilized at a low level since then (Ref. 59043). It has been suggested that members of the genus Alosa are hearing specialists with the American shad (Alosa sapidissima) having been found to detect and respond to sounds up to at least 180 kHz (Ref. 89631). This may aid in predator avoidance (e.g. cetaceans) (Ref. 89632). Hybridization between this species and the allis shad (Alosa alosa) has been reported from the Rhine (Ref. 89633) as well as rivers in France and Algeria (Ref. 10541). There is some evidence that indicates that shad hybrids may reproduce (Ref. 27567).
  • Whitehead, P.J.P. 1985 FAO Species Catalogue. Vol. 7. Clupeoid fishes of the world (suborder Clupeioidei). An annotated and illustrated catalogue of the herrings, sardines, pilchards, sprats, shads, anchovies and wolf-herrings. FAO Fish. Synop. 125(7/1):1-303. Rome: FAO. (Ref. 188)   http://www.fishbase.org/references/FBRefSummary.php?id=188&speccode=24 External link.
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Description

 Alosa fallax is a member of the herring family. It is a planktivorous fish with silvery white sides and a deep blue colouration on its back. It is most commonly recorded at a size between 20-40 cm but has been reported to reach 60 cm. Like other shads its upper jaw is distinctly notched in the mid line and the gill cover has distinct radiating ridges.The twaite shad is distinguished from the other European shad, the allis shad (Alosa alosa), by having between 40-60 gill rakers on the first gill arch while Alosa alosa has between 80-130 (Whitehead, 1985). The twaite shad is anadromous in that it spends its life in the ocean but enters rivers in April and May to spawn before returning to the sea. Juveniles remain in the rivers for up to 24 months (Muus & Nielson, 1999).
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Distribution

Range Description

Southern shore of Baltic, North Sea northward to Bergen, Atlantic coasts from Scotland and Ireland to Morocco, northern Mediterranean (and Nile) and rarely in northern Black Sea occasionally east to Crimea, from where adults ascend rivers, migrating a short distance upstream to spawn. Ascended Drin to Lake Ohrid. Earlier ascended Rhône for 600 km.
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Northeast Atlantic: from the British Isles and southern Norway to Morocco, including the Baltic, Mediterranean and Black Seas (Refs. 188, 26334, 51442)). Several subspecies have been recognized based on the number of gill rakers and geographical location (Ref. 10541) and some have since been given species-status (Ref. 59043).Listed in Appendix III of the Bern Convention (2002). Listed in Annex II and V of the EC Habitats Directive (2007).
  • Whitehead, P.J.P. 1985 FAO Species Catalogue. Vol. 7. Clupeoid fishes of the world (suborder Clupeioidei). An annotated and illustrated catalogue of the herrings, sardines, pilchards, sprats, shads, anchovies and wolf-herrings. FAO Fish. Synop. 125(7/1):1-303. Rome: FAO. (Ref. 188)   http://www.fishbase.org/references/FBRefSummary.php?id=188&speccode=24 External link.
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Baltic Sea, North Sea, Eastern North Atlantic and adjacent estuaries.
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Physical Description

Morphology

Dorsal spines (total): 4 - 6; Dorsal soft rays (total): 12 - 16; Anal spines: 3 - 4; Analsoft rays: 16 - 22; Vertebrae: 55 - 59
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Size

Maximum size: 550 mm SL
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Max. size

60.0 cm SL (male/unsexed; (Ref. 35388)); max. published weight: 1,500 g (Ref. 188); max. reported age: 25 years (Ref. 556)
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Diagnostic Description

Body slightly compressed, fairly deep with scutes along belly. Upper jaw notched, lower jaw fitting into it (Ref. 188). 31-50 (rarely up to 60) thick gill rakers on the lower arc (Ref. 59043). Large, thin scales (Ref. 51442). Deep blue dorsally, becoming greenish brown or golden on the sides and silvery ventrally. A dark spot posterior to gill opening followed by 6-10 similar spots (sometimes faint or absent) along flank (Refs. 188, 88187). Also Ref. 2196.
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Habitat:
At sea, pelagic. Juveniles remain close to shore and estuaries. Migrates from sea to rivers, spawns in main river often only few kilometres above limit of brackish water. Spawning also reported from small rivers over gravel bottom.

Biology:
Anadromous. Males migrate upriver at 2-3 years, females at 3-4. Many individuals spawn 3-4 seasons. Adults congregate near estuaries in April and enter rivers when temperatures reach 10-12°C, mainly in May-June. Spawning starts when temperature reaches about 15°C or more, in May-June. Spawns in large, very noisy schools near surface after midnight. Eggs sink to bottom or are pelagic. Spent fish migrate back to sea. Most juveniles migrate to river mouth during first summer and move to sea at end of second year, where most shads remain until they mature. Individual fish are thought to return to their natal spawning site. At sea, feeds predominantly on crustaceans and small fishes. In freshwater, adults do not feed. Juveniles prey on planktonic crustaceans.

Systems
  • Freshwater
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Environment

pelagic-neritic; anadromous (Ref. 51243); freshwater; brackish; marine; depth range ? - 300 m (Ref. 10541)
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Depth range based on 1131 specimens in 1 taxon.
Water temperature and chemistry ranges based on 478 samples.

Environmental ranges
  Depth range (m): -9 - 153
  Temperature range (°C): 2.641 - 11.856
  Nitrate (umol/L): 1.194 - 10.454
  Salinity (PPS): 6.114 - 35.546
  Oxygen (ml/l): 0.982 - 8.164
  Phosphate (umol/l): 0.306 - 2.380
  Silicate (umol/l): 1.624 - 51.283

Graphical representation

Depth range (m): -9 - 153

Temperature range (°C): 2.641 - 11.856

Nitrate (umol/L): 1.194 - 10.454

Salinity (PPS): 6.114 - 35.546

Oxygen (ml/l): 0.982 - 8.164

Phosphate (umol/l): 0.306 - 2.380

Silicate (umol/l): 1.624 - 51.283
 
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 Coastal waters returning to freshwater to spawn usually above shallow gravel substrates near deeper pools. It is a schooling and migratory species and spends most of its life offshore.
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Migration

Anadromous. Fish that ascend rivers to spawn, as salmon and hilsa do. Sub-division of diadromous. Migrations should be cyclical and predictable and cover more than 100 km.
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Trophic Strategy

In freshwater, juveniles feed on planktonic crustaceans, rotifers and insects (Ref. 35387). In estuaries they consume mysids, isopods, and amphipods (Ref. 42360).In the sea, adults feed mainly on small fishes and on crustaceans, including euphausiids (Refs. 188, 42360). Although feeding generally ceases during spawning migrations (Ref. 59043), some male individuals were found to feed on copepods, isopods, fishes and insects (Ref. 89633).
  • Whitehead, P.J.P. 1985 FAO Species Catalogue. Vol. 7. Clupeoid fishes of the world (suborder Clupeioidei). An annotated and illustrated catalogue of the herrings, sardines, pilchards, sprats, shads, anchovies and wolf-herrings. FAO Fish. Synop. 125(7/1):1-303. Rome: FAO. (Ref. 188)   http://www.fishbase.org/references/FBRefSummary.php?id=188&speccode=24 External link.
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Life History and Behavior

Life Cycle

Adults in the sea begin to congregate near mouths of estuaries in April. Enter estuaries and ascend rivers in May and June when water temperature is between 10-14 °C (Refs. 188, 51442, 59043, 89636). Males begin such movements at 2-3 years, females at 3-4 years (Ref. 59043). Although movement upstream is usually limited to a few kilometres above the brackish zone (Refs. 59043, 89486), spawning has also been reported in non-tidal freshwater areas up to 400 km upstream (Ref. 89637). Gametogenesis occurs in the estuaries. Early arrivals in the rivers are mostly males, with the sex ratio becoming more equal with the later arrivals (Ref. 42360). Spawning movements occur with spring tides and peak when river discharge levels are high (Refs. 89636, 89638). However, when flows are too high, movements upstream become limited (Refs. 89636, 89639). Spawn when water temperature is anywhere between 12-22 °C (Ref. 10541). Move to riverine spawning grounds at night; spawn in large, very noisy schools near surface and leave these areas before daybreak (Ref. 10541). Spawning sites consist of sand and gravel areas with flowing water (Ref. 10541). Spent adults return to the sea and may spawn for 3-4 seasons throughout their lifetime (Refs. 30578, 51442, 59043). Most individuals will have lost 22 % of their body weight after spawning (Ref. 89640). There is some evidence that most individuals return to their natal rivers to spawn (Refs. 10541, 59043). Eggs either drift with the current or sink to the bottom (Ref. 59043, 89641). Eggs hatch after 2-8 days, depending on water temperature (optimal 15-25 °C) (Refs. 35387, 41851). Larvae and juveniles move towards the estuaries and river mouths during their first summer and to the sea at the end of their second year (Ref. 59043). Males mature mainly between the ages of 2-5 years, females between 3-7 years (Ref. 188, 2163, 10541). Length at maturity is between 30-40 cm total length (Ref. 88187).
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Alosa fallax

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 10
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2008

Assessor/s
Freyhof, J. & Kottelat, M.

Reviewer/s
Bogutskaya, N., & Smith, K. (IUCN Freshwater Biodiversity Unit)

Contributor/s

Justification
Now only very locally distributed (large estuaries), a victim of pollution and impoundment of large rivers throughout Europe. Most populations declined during first decades of 20th century. Current status of the species is good and is increasing in the North Sea and Baltic.

History
  • 1996
    Data Deficient
    (Baillie and Groombridge 1996)
  • 1996
    Data Deficient
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Population

Population
Quite common in north sea basins and French Atlantic coast. Populations increasing in the Baltic

Population Trend
Stable
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Threats

Major Threats
Dams blocking spawning sites, pollution.
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Least Concern (LC)
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Management

Conservation Actions

Conservation Actions
It is a (EU - Berne Convention) Natura 2000 species, requiring protection from range states.
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: minor commercial; price category: low; price reliability: reliable: based on ex-vessel price for this species
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Wikipedia

Twait Shad

The twait shad or twaite shad (Alosa fallax) is a species of fish in the Clupeidae family.[1] It is an anadromous fish which lives in the sea but migrates into fresh water to spawn.

Description[edit]

The twait shad is a typical herring-type fish and much resembles the allis shad. It has no lateral line and the belly is more rounded than that of the sprat and Baltic herring. The gill cover is ridged and the caudal peduncle has large, plate-like scales. This fish is more colourful than the Baltic herring. 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 there are a distinctive row of six to ten large dark spot just behind the gill cover though these may fade when the fish is dead. The adult length is typically 25 to 40 cm (10 to 16 in).[2]

Distribution[edit]

The twait shad is found in most of Europe and all countries bordering the Mediterranean Sea.[1]

Biology and Life-cycle[edit]

Alosa fallax has a similar lifecycle to Alosa alosa (allis shad). They are known to live in sympatry with Alosa alosa.[3] Some studies have suggested that the Alosa fallax and Alosa alosa species can hybridize.[4] They are anadromous species just like many other species in the Alosa genus.[4] However, there is some record of them being landlocked suggesting an ability to adapt well to their environment.[4] They primarily live at sea on feeding grounds and will migrate to their spawning grounds between April and June once they are sexually mature.[4] Maturity usually ranges from 3–7 years of age.[4] It is observed that juveniles appear in estuaries, brackish water, around June to July.[3] The salinity of brackish water may impose problems to the juveniles migrating from freshwater.[3]

Population Reduction[edit]

Populations have been reduced primarily through overfishing, pollution, and habitat destruction.[4] Hybridization between species is more likely with species affected by human disturbances.[4] It is estimated that the estruarine phase, or the time that they are in the estuaries migrating from spawning grounds to sea, has a duration in Alosa fallax of up to a year and a half.[3] The estimate however does not take into account individual variation and/or survival of juveniles in the estruarine phase.[3]

Conservation[edit]

Four special areas of conservation have been designated in Ireland where Alosa species have been known to spawn.[4] Alosa fallax "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." [3]

References[edit]

  1. ^ a b c Freyhof, J. & Kottelat, M. (2008). "Alosa fallax". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 31 January 2014. 
  2. ^ "Allis shad: Alosa alosa". NatureGate. Retrieved 14 December 2013. 
  3. ^ a b c d e f 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.
  4. ^ a b c d e f g h 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.
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