Alosa alosa (Linnaeus, 1758), Allis shad (Clupeidae)

Author: Ronald Fricke, Germany

1. Description of the habitat/autecology of the species

The Allis shad Alosa alosa is a species that spends most of its life in the open water of coastal oceans, and anadromously migrates into large rivers for spawning. When maturing, adults stop feeding, enter estuaries, and then from April to June they migrate as far upstream as possible, with the males first arriving to find spawning sites, and the females following 1-2 weeks later. They spawn repeatedly during several nights, from May to June, above clean gravel beds, and mostly die immediately after. A single female can spawn 50,000 to 600,000 eggs that float towards the ground, mostly remaining close to the spawning site, but some drifting downstream for up to 30 km. After hatching, larvae and juveniles live in slow-flowing stretches along deeper parts of the river; after 3-4 months, they have reached a total length of 8-12 cm, and start their downstream migration towards the sea, where they remain and grow for 3-11 years until maturation. Juvenile allis shad feeds on mosquito larvae and crustacea, adults on planktonic crustacea, fish larvae and young fish (Fricke, 1987: 62; 2004: 22-24).  Maximum total length 69 cm (male), 83 cm (female); maximum body weight 4 kg; maximum individual age 11 years.

2. Distribution (past and present)

The historical distribution range of this species includes an area from the Kattegat to the western and eastern Gotland Sea including adjacent rivers and streams. It has been rare since the 1800´s in most parts of Baltic Sea, occurring occasionally as a straggler (Fries et al 1895). In Finland, two specimens have been recorded, one in 1891 and one in 2002. Allis shads of different river systems are probably genetically distinct, as adults usually return to the same river where they hatched (Quignard & Douchement, 1991). Outside the HELCOM area, Allis shad occurred historically from the southern Norway and Scotland to Morocco, but is now restricted to an area from the southern North Sea to Portugal.

3. Importance (sub-regional, Baltic-wide, global)

The Baltic Sea populations of Alosa alosa are (historically) considered to have been of local importance in the HELCOM area, according to the HELCOM (2007) definition.

4. Status of threat/decline

This species is threatened and its populations have been severely declining throughout its distribution range in the HELCOM area and beyond in other European waters; the last area where the species is reasonably common is the Gironde system in France. In a HELCOM assessment, this species is classified as critically endangered (CR) according to IUCN criteria in the HELCOM area and as a HELCOM high priority species (HELCOM, 2007). The species is listed as critically endangered (CR) by Germany, and as endangered (EN) by Denmark. It does not reproduce in Sweden or Finland, why it was considered not applicable (NA) by Sweden. The species is also included in Annexes II and V of the EU Habitats Directive (under the name Alosa spp.).

5. Threat/decline factors

Threatened by a variety of factors: it is a target species of (historical) fisheries, it is caught as by-catch in pelagic and river fisheries,  eutrophication degrades its spawning sites (as the species spawns on clean gravel bottoms), and construction in rivers (dams and weirs) inhibit its spawning migration). The species is considered to be very rare and highly sensitive, but not a keystone species, in the HELCOM area. Additional actions are needed in the OSPAR area to support the North Sea populations of Alosa alosa.

6. Options for improvement

In the HELCOM area, Allis shad would benefit from restoration of potential spawning sites, and reduction of eutrophication in the spawning rivers. Later restocking programmes may be effective, if suitable fish material can be obtained.

7. References

Fricke R., 2004.  Der Maifisch (Alosa alosa).  Offenbach am Main (Verband Deutscher Sportfischer), 39 pp.

Fries, B. Smitt, F. S. Von Wright, W. 1895. Skandinaviens fiskar. Stockholm.

HELCOM 2007. HELCOM Red list of threatened and declining species of lampreys and fish of the Baltic Sea. Baltic Sea Environmental Proceedings, No. 109, 40 pp.  Available in: http://www.helcom.fi/stc/files/Publications/Proceedings/bsep109.pdf

Quignard J.P. & Douchement C. 1991. Alosa alosa (Linnaeus, 1758). Pp. 89-126.  In: Hoestlandt, H.: The freshwater fishes of Europe. Vol. 2. Clupeidae, Anguillidae.  Wiesbaden (Aula-Verlag), 447 pp.