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Conservation The biology of Danube sturgeons © Copyright Hartmut Jungius / WWF-Canon

Sturgeons originated about 200 Migrating up the Danube million years ago and have undergone Five of the six sturgeon species native little morphological change, making to the Danube basin used to live in the them “living fossils”. They show very Black Sea and enter the Danube for long generation intervals, tolerance for spawning. In the past, Russian wide ranges of temperature and Sturgeon, Stellate Sturgeon, European salinity, and high resistance to Sturgeon (very rare and now extinct in natural predators. The 27 members the Danube), Ship Sturgeon and of the sturgeon order Beluga Sturgeon regularly migrated (Acipenseriformes) are confined to the upstream, some as far as Vienna and northern hemisphere, inhabiting beyond. However, this migration has rivers, lakes and coastal waters in been interrupted by the Iron Gates Europe, Asia and America. dams shared by Serbia and Romania. Today, the migration of these species Sturgeons are distinctive for their can be observed only in the Lower LITTLE elongated bodies, extended upper Danube. The Sterlet, on the other lobes of the caudal fin and the hand, is a pure freshwater species and IS KNOWN rostrum-shaped snouts. They lack largely sedentary, undertaking only scales but have five rows of bony short spawning migrations. The Ship ABOUT KEY scutes along the body. Sturgeons can STURGEON HABITATS Sturgeon seems to have survived only get more than 100 years old and over in its freshwater form. IN THE DANUBE six meters long. THE BIOLOGY OF DANUBE STURGEONS WWW.DANUBE-STURGEONS.ORG For more information: For more www.danube-sturgeons.org is very long with puberty occurring late in life. Individuals The project “Joint actions to raise awareness on overexploitation of Danube sturgeons in Romania and Bulgaria” aims to tackle overfishing, the main direct threat to the survival of Danube sturgeons. Acipenseriformes Sturgeons possess tactile barbels located at the front of the mouth, which is protactile – meaning that it can be pushed outwards also and forwards. They have thickened lips. Their eyes are very small and it is thought that they do not contribute much to the location and capture of prey. Most Danube sturgeon species feed on bottom invertebrates - insects, insect annelids larvae, and molluscs, and also occasionally on bottom fish. Some species reduce or even stop feeding during their migration in freshwater. is the only true Huso huso predator among the six Danube sturgeon species. In the Black Sea it preys on bottom-dwelling and pelagic fish, while in the river it feeds on freshwater fish. We know little about the exact location of keyWe know little about the exact location sturgeon habitats within the Danube River basin. Suitable spawning habitats are vital for the reproduction of Acipenseriformes. Spawning sites are usually hard surfaces covered with clay, gravel and boulders, and featuring many crevices in which larvae find protection predators from or floods. Location of spawning sites varies according to the hydro-morphological characteristics of the different reaches of the river. The water depth at spawning sites varies from a few meters to 26 m and the required current velocity is quite high, dispersal allowing for wide of fertilised eggs. Eggs are adhesive and after dispersing from spawning settle grounds, to the bottom, usually on coarse substrates in a much lower water velocity. remain They there until they develop into larvae and start feeding. Flow regime and water temperature important factors are in development early of life stages of sturgeons. Water level fluctuations, due to flow management by hydropower stations, can have negative effects on spawning and reproduction success of adults. Most Danube sturgeon species spawn sturgeon species Most Danube to early summer from spring over a wide range of races (6 to 25° C). Some temperatures some in autumn in spring and enter or river the spend of the winter race winter. Fish in holes hibernating the winter or deeper in the river, far upstreamriver bends. They spawn the year after spring The races do entering the river. enter the rivernot hibernate and only when temperatures two are rising. The forms of different species,behavior do not represent but different strategies for the pre-spawning migration. populations show thatObservations on some sturgeons visit the same spawning sites every the river for spawning.time when they enter “site The fidelity” may derive from the fact that the river due to geneticallysturgeons survive in early imprinted strategy life stage survival in a particularadapted to the location reach of the river. The life cycle of spawn repeatedly, but most females do notspawn repeatedly, but most females do spawn annually. Sturgeons have also shown a tendency towards hybridisation with other sturgeon species. This occurs even more when spawning habitats are lost different and species are confined to only a few suitable sites or when one species is rare compared to another species. Feeding Spawning habitats Spawning habits Spawning Why we are here. natural environment and stop the degradation of the planet’s To to build a future in which humans live in harmony with nature. www.danube-sturgeons.org EUROPEAN STURGEON / STURIO ACIPENSER SHIP STURGEON / NUDIVENTRIS ACIPENSER STERLET / RUTHENUS ACIPENSER STELLATE STURGEON / STELLATE STELLATUS ACIPENSER BELUGA STURGEON / HUSO HUSO RUSSIAN STURGEON / GUELDENSTAEDTI ACIPENSER