Star sturgeon  (Acipenser stellatus)

The star sturgeon is classified as Critically Endangered (CR) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

Belonging to an ancient group of fish, the prehistoric-looking star sturgeon (Acipenser stellatus) is notable for being one of the three main caviar producing sturgeon species (2). Reaching over two metres in length, the star sturgeon’s elongated body is armoured with rows of hard, spiky, white nodules, which brightly contrast with the blackish-grey upperparts. Like other sturgeons, the star sturgeon’s mouth is found on the underside of its head, with a cluster of short barbells located between the mouth and the tip of its long, pointed snout. The tail fin is uneven, with a small, short lower lobe and a much larger upper lobe extending upwards and away from the body (4).

The star sturgeon inhabits the Black, Caspian and Azov Seas, and associated rivers and waterways such as the Danube (1) (2). Individuals have also been found in the Adriatic Sea, off the west coast of Italy, and in the Aegean Sea, around the coasts of Greece and Turkey (5)

The star sturgeon can tolerate a range of habitats, from the salty waters of the Aegean and Adriatic Seas, to the freshwater conditions of the Danube (2) (5).

Commonly found in coastal waters, the star sturgeon spends the day close to the seabed, where its downward-facing mouth helps it to feed on bottom-dwelling organisms, such as worms, molluscs and small fish (2) (4). At night, the star sturgeon becomes more active, rising up to the water surface to find other sources of prey (4).

In order to reproduce, the star sturgeon must undergo a migration from the sea into a freshwater river, swimming upstream to the spawning ground. Interestingly, there are two separate “races” of star sturgeon, which display different spawning behaviours. One race migrates and spawns during spring and summer, while the other migrates in the winter, over-winters in the river and spawns in the following spring (2). A single female produces a vast amount of eggs, in the order of hundreds of thousands, which stick to river vegetation and stones (6).

Generally, it is only the juvenile star sturgeons that are threatened by predation, as the large size and armour of the adults helps to deter predators (2) (6). Nevertheless, on occasion, the parasitic, eel-like lamprey has been known to cause fatal injuries to adult star sturgeons (6).

The major threat to the star sturgeon’s survival is overfishing for its meat and, more significantly for caviar, sold under the name “sevruga”. This is produced from the sturgeon’s unfertilised eggs and is almost always extracted by killing the female. The caviar industry is currently in crisis, as the dwindling stocks of the star sturgeon, and the other major caviar producing species, can no longer provide sufficient caviar to meet the huge worldwide demand (2). Despite attempts to manage star sturgeon stocks, illegal fishing and black market trade in caviar are threatening to drive this already endangered species to extinction (2) (7).

The threat of overexploitation for the caviar trade is also exacerbated by a reduction in the star sturgeon’s natural spawning grounds due to the construction of hydroelectric power stations and reservoirs, and also by the high levels of pollution found throughout its range (2).

In 1998, the star sturgeon was listed by the Convention on International Trade in Endangered Species (CITES), meaning that all international trade in this species is controlled by maximum export quotas and trade permits (2) (3). The countries which are party to the CITES agreement must agree on sustainable catch and export quotas based on scientific surveys, and must adopt regional conservation strategies and attempt to combat illegal fishing. The strict enforcement of these regulations meant that in 2006, caviar export was banned for all of the countries bordering the Caspian Sea, since the countries failed to provide sufficient information about the sustainability of their catch. This promoted an agreement between the countries to reduce their star sturgeon caviar export quotas in 2007 by over 25 percent (8). The countries bordering the Black Sea have adopted an even stricter policy regarding their sturgeon stocks, maintaining a zero quota policy, which has continued into 2008 (9). Whether these reduced quotas will prove sufficient to allow the star sturgeon’s population to recover remains to be seen.

Due to limited natural spawning grounds, a high proportion of star sturgeon stock in the Caspian and Azov seas is maintained by farm-grown fish released into the wild. Unfortunately, however, poaching has reduced the numbers of adult star sturgeons so dramatically that hatcheries are struggling to obtain enough breeding fish to conduct artificial propagation (2). In an attempt to control the illegal trade in this species, in 2007 a world database for caviar trade was set up to monitor the origin of exported caviar and track shipments around the world (10).

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more about sturgeon conservation: 

• World Sturgeon Conservation Society:
  www.wscs.info