Description:
Dorsal
scutes 9-16, Lateral scutes 24-40, Ventral scutes 8-15. Gill rakers 15-29.
A. sturio of the Baltic sea is characterised by lower numbers of dorsal and lateral scutes and resembles very closely to A. oxyrinchus.
The snout is long and wide, averaging 7.2% of the total length. With size it becomes more blunt, decreasing from 65% to 32% of head length. The barbels are located midway or slightly closer to the mouth in young, than to the tip of the snout, as in old. Nummerous rhombic platelets between dorsal and lateral rows of scutes.
Coloration varies between black and golden green on the dorsal side, the ventral skin is white to grey.
Distribution:
The common sturgeon is the only sturgeon species that has previously been distributed all over Europe. It once ranged from the White Sea, the Baltic Sea, the North Sea, the Atlantic, the Mediterranean to the Black Sea. Previously ascending all major rivers for spawning.
In the Baltic the rivers Neva, Daugava, Vistula, Odra with Wartha; In the North Sea the rivers Eider, Elbe with Havel, Saale and Moldau to Prague, the Oste, Weser to the confluence of Werra and Fulda, Ems, Rhine to Basel with the tributaries Lippe, Mosel to Toul, Main to Schweinfurt and Neckar to Heilbronn, the Maas to Liège, the Schelde to Gent, the Themse, Trent, Severn to Newnham, and Seine to Paris with Marne; in the Atlantic the rivers Loire, Gironde with Garonne and Dordogne, Adour, Douro, Guadalquivir; In the Mediteranean the rivers Juca, Ebro, Rhone with Saone and Doubs, Tiber; In the Adriatic Sea the rivers Po, Isonzo, Neretva, Drina, Buna, Pinios, Struma und Meric as well as in the Black Sea the rivers Danube, Rioni, Yesil Irmak and Kizil Irmak were once frequented on a regularly basis during the spawning migrations.
Ecology:
The common sturgeon is a typical migratory sturgeon that ascends fresh water for spawning only. Otherwise d´welling in marine and brackish waters. Tagging experiments show long distance migrations of more than 3000 km for feeding migrations.
Food consists mainly of worms (Aphrodita, Tubifex, Nephthys, Stylaroides), molluscs, crustaceans (Mysis, Gammaracanthus, Pontoporeia, Echinogammarus, Crangon, Carcinus) and small fish (Ammodytes, Engraulis).
A. sturio can reach up to 6 m in lenght and 600 kg in weight. The maximum age reported is 60 years. The average catch consisted of individuals 2 m in lenght and 90 kg in weight.
Sexual maturity in females is reached at an age of 11-18 years and a size of 1.5-1.8 m. In males sexual maturity is observed after 9-13 years and 1.3-1.6 m. Intervals between spawnings differ throughout the species´ range, and vary from 1-3 years according to sex.
The spawning season varies with water temperatures between April and July. Spawning occurs in groups consisting of one female and several males over rocky or gravel substrate at water velocities of 1.0-1.5 m/sec and water temperatures from 13-22° C. Spawning in brackish water has been reported but seems unlikely.
Spawning migrations depend on the hydrological regime. Upstream migrations of up to 1000 km have been reported. Males reach spawning sites up to 3 weeks prior to females.
Egg size varies between 2.5 and 3.0 mm. Specific fecundity varies between 12,000 and 30,000 eggs per kg body weight. Hatching occurs at water temperatures between 7 to 22°C after 3-14 days. After 11-14 days external feeding is begun at a size of 16-18 mm.
The juvenile sturgeons remain in freshwater for 1-2 years and then descend into the brackish waters of the estuary. Here regular migrations between the estuary and the sea occur during the first years of the juvenile stage. Adults ascend the rivers immediately after spawning.
Economy:
During the last quarter of the 19th century, North and Baltic
seas catches comprised up to 200 mt/a. Due to overfishing, hydro-construction, gravel
extraction and pollution of the rivers, the Common sturgeon is almost extinct today. Only
in the rivers Rioni and Gironde, small stocks have been proven to persist.
Acipenser sturio is included in the New York Convention for Species protection (IUCN), the Convention on International Trade in Endangered Species of wild fauna and flora (CITES, Appendix I.) and in the adendulum of the priority list of protected species of special interest to the European Union (EU, Appendix A).
This is an extract of the book:
The Sturgeons and Paddlefishes (Acipenseriformes) of the World
© by Martin Hochleithner