Acipenser nudiventris

Ship sturgeon (A. nudiventris) (Apatin, Danube River Km 1390 - Serbia - 31 Oct 2003). Photo Credit: Predrag Simonovič, University of Belgrade, Serbia

 

1- General information

The common name of this species is “Ship Sturgeon” or “Fringebarbel Sturgeon”. The scientific name “nudiventris” stems from Latin and means “naked belly”. This is due to the fact that the bony plates on the bellies of adult fishes get rubbed off with age and are often almost fully lost.

 

2- Occurrence

In a lot of rivers this species occurs only in its sea-migrating form. It inhabited the Black, Azov, Caspian and Aral Seas, from where the spawners migrated upstream the rivers for spawning. However, in the Danube River the Ship Sturgeon has solely been documented in its freshwater form that remains in the river throughout its entire life.

 

A. nudiventris was formerly recorded in the Lower and Middle Danube (occasionally also in the Delta) – migrating upstream as far as Komarno, 1,766 km from the river mouth, and even Bratislava at km 1,869 – but only rarely entered Austrian waters. Occasionally it also occurred in the following Danube tributaries: Vah, Tisza, Sava and Drava, and in the lower sections of the Prut and Siret.

 

The Ship Sturgeon was never abundant in the Danube River Basin. Verification on the basis of historical documents is difficult, since young ship sturgeons can easily be confused with sterlets (A. ruthenus) and older fishes with the Danube sturgeon (A. gueldenstaedti). Fishermen often did not distinguish between these different species.

 

3- Biology

The Ship Sturgeon is a rather large species and can reach lengths of more than 2 meters. A maximum age of 36 years was recorded in the Kura River (Caspian Sea Basin). It takes males and females up to 9 and 14 years, respectively, to mature. The females carry 200,000 to 1,300,000 eggs, depending on their size.

 

The Ship Sturgeon feeds mainly on bottom dwelling organisms such as insect larvae, mussels, snails, crabs and small crayfish. The optimum temperature range for the egg development of this species is between 11 and 15 °C and spawning occurs when temperatures reach this level.

 

4- Spawning migration

There is absolutely no information on spawning sites in the Danube Basin; in the Kura River (Caspian Sea Basin) and Amu-Darya River (Aral Sea Basin) spawning takes place on gravelly or stony bottoms or along sections with firm, clayey sediments and strong water currents.

 

5- Status and conservation

A. nudiventris is recorded very seldom in the Danube River Basin nowadays. The species has disappeared completely from the Austrian and Slovak stretches of the Danube, and it is extremely rare in the Hungarian section. However, the capture of ship sturgeons in the Danube near Apatin, (October 2003/ Serbia), in the Mura (May 2005/ close to its confluence with the Drava in Hungary) and in the Danube near Mohacs (December 2009/ Hungary) confirmed the species’ continuing presence in the Middle Danube Basin. There have been no documented catches from the Lower Danube for 30-40 years.

 

This species is extremely rare and it is debated whether the Danube population has already reached its “point of no return” and is vanishing in the near future. Virtually nothing is known about the life-cycle of this species in the Danube River. According to the IUCN Red List (2010) Acipenser nudiventris is critically endangered. Rescue measures are overdue and most urgently needed.