Acipenser sturio (Linnaeus 1758), Sturgeon (Acipenseridae)

Author: Ronald Fricke, Germany

1. Description of the habitat/autecology of the species

Acipenser sturio is living demersally above sand and mud bottoms, in the ocean from inshore coastal waters down to 50 m depth. The species usually occurs solitarily. As an anadromously migrating fish, it enters rivers for reproduction, and spawns at depths of 2-10 m over stony bottoms. Females produce 800,000 to 2,400,000 sticky eggs which adhere to the stones. After hatching, juveniles migrate slowly into the estuary, then into the sea where they spend at least 7-9 years (usually 15 years) before they mature and start their spawning migration again. Sturgeons feed on crustaceans, molluscs, polychaete worms, and small fishes (Fricke, 1987: 57; Gessner & Ritterhoff, 2004; Froese & Pauly, 2005). Maximum total length 500 cm (males), 600 cm (females); maximum body weight 400 kg; maximum individual age 100 years.

2. Distribution (past and present)

Kattegat area is part of the historical distribution range of this species. At present, it is extinct there but may still be occurring as a straggler. Outside the HELCOM area, this species was historically distributed from Norway to Morocco, as well as in the Mediterranean and Black sea. The last known population exists in the Gironde/France, with adults straggling north to the greater North Sea area; possibly another population extant in Kızılırmak River/southern Black Sea, Turkey. In the Baltic Sea Proper, this species was replaced by A. oxyrinchus, which is now also (practically) extinct.

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

The species was historically neither of local nor global importance in the HELCOM area, at least not during the past 1,000 years.

4. Status of threat/decline

This species' populations have been severely declining to extinction throughout its distribution range in the HELCOM area, and severely declining in other parts of its distribution range. In the HELCOM area, this species is classified as extinct (EX) according to IUCN criteria ,and as a HELCOM high priority species (HELCOM, 2007). The species is listed as extinct (RE/EX) by Sweden. It is included in the Annex II of the EU Habitats Directive; also as a priority species in the OSPAR List (Anonymous, 2004). A. sturio is considered as critically endangered by IUCN (Baillie et al., 2004). It is also listed on CITES (Annex II).

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 demersal and river fisheries, eutrophication degrades its spawning sites (as the species spawns on clean bottoms), and construction in rivers (dams and weirs) barrier its spawning migration and cause too strong water velocity for the spawning migration of this slow-moving fish. The species used to be common, but is now extinct, and highly sensitive to human activities.

6. Options for improvement

This species needs immediate action to prevent extinction. The main action, however, would be required outside HELCOM area in the neighbouring OSPAR area, and in the Black Sea region. Conservation schemes should include fisheries restrictions, freshwater and marine protected areas, measures to reduce eutrophication of the spawning rivers, construction of special fish passes or sturgeon elevators around weirs, and scientifically advised restocking programmes into suitable rivers over an extended period of time.

7. References

Anonymous 2004. 2004 Initial OSPAR List of Threatened and/or Declining Species and Habitats (References number 2004-06). OSPAR Convention on the Protection of the Marine Environment of the North-east Atlantic, Meeting of the OSPAR Commission (OSPAR), Reykjavik, 28 June-1 July 2004.

Baillie J.E.M., Hilton-Taylor C. & Stuart S.N. 2004. 2004 IUCN red list of threatened species. A global species assessment.  Gland & Cambridge (IUCN).

Froese R. & Pauly D. (eds) 2005. FishBase. Available in: www.fishbase.org, version (11/2005).

Gessner J. & Ritterhoff J. (eds.) 2004. Species differentiation and population identification in the sturgeons Acipenser sturio L. and Acipenser oxyrhinchus.  BfN-Skripten, 101, 2004.

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