Acipenser sturio

Common, Atlantic or European sturgeon (A. sturio) Image credit: Wikipedia, image is in the public domain; taken from the book “British Freshwater Fishes” by A.F. Lydon (1879).

 

1- General information

The common name for this species is Common sturgeon, Atlantic sturgeon or European sturgeon. The common English name "Atlantic sturgeon" is also used for another sturgeon species Acipenser oxyrinchus from North America, which also colonized the European Baltic Sea since the early Middle Ages but never the European Atlantic coast or the Black Sea. This sometimes leads to confusion when just using the common name.

 

2- Occurrence

Acipenser sturio occurs exclusively in Europe and West Asia and is confined to the North-eastern Atlantic Ocean, especially to shallow parts of the North Sea, and some coastal waters in the Mediterranean and Pontic region, including the Ligurian, Tyrrhenian, Adriatic, Ionian, North Aegean, Marmara and Black Seas. Within these regions, the species once migrated into all major river systems to spawn. In the Black Sea Basin, A. sturio formerly migrated into the Lower Danube River, the Inguri/Dzhvari and Rioni Rivers in Georgia, and the Yesil Irmak and Kizil Irmak in Turkey. Nowadays the species is close to extinction throughout its former range and it has already gone extinct in the Danube.

 

3- Biology

Not much is known about the Danube population of this species but an overall maximum length of 6 meters and a maximum age of 48 years were documented in other populations. It takes the male and female up to 9 and 14 years, respectively, to mature. The female spawners can carry 790,000 to 1,820,000 eggs, depending on their size.

There is little information on diet for this species. When in fresh water, the juveniles feed on small animals like e.g. the larvae of aquatic insects, worms, small crabs, shrimp, mussels and snails. Adults feed on small bottom-dwelling animals, such as mussels, snails, worms, crabs, shrimps and sometimes even small bottom fishes.

 

4- Spawning migration

A. sturio is a sea-migrating species where these sturgeons spend most of their adult life in the shallow water on the continental shelf, especially in estuaries with muddy bottoms. They enter rivers for spawning from January to October, with peak migration usually occurring in periods of high water between early April and the end of May. The exact dates depend on the geographic location of the river. Southern populations begin to appear in rivers earlier than northern populations.

 

Spawning takes place in deep pools with strong currents over a rocky or pebble bottom, either in the main channel or in branches. Most young-of-the-year stay in rivers close to the spawning grounds where they hatched, but some move downstream to estuaries during their first summer.

 

5- Status and conservation

A. sturio was always the rarest sturgeon species in the Black Sea Basin and its presence was only documented at the beginning of the 20th century. Single specimens were then recorded from the catches of fishermen in both the Danube River and the Black Sea. It seems likely that this species also spawned in the Lower Danube since young-of-the-year and hybrids with other species were described in the 1930s, suggesting simultaneous spawning with other sturgeons on the sand banks off the Danube Delta. Reports of A. sturio from Bulgarian and Serbian stretches of the Danube are contradictory. According to one source, the last record of A. sturio in Serbia was in 1954.

 

According to the IUCN Red List (2010) Acipenser sturio is critically endangered. This basically refers to Western Europe, as nowadays, this species has disappeared from its southeastern range in the Black Sea and the Danube River. It may take a long time before a restoration programme for this species in the Danube River and the Black Sea is possible, due to the endangered status of this species throughout its former range and the scarcity of broodstock for conservation purposes.