species of the week #90 – beluga sturgeon

The Beluga Sturgeon is a fascinating giant that was once also found in the Danube. According to tradition, the fish, which can be up to eight metres long, migrated over 2,000 kilometres from the Black Sea to its spawning grounds in the Danube and its tributaries. Today, this route is blocked by dams and locks, especially the power plants at the Iron Gate between Serbia and Romania. Unfortunately, the linnet is also still hunted. Its spawn is considered the most productive and tastiest caviar.

The beluga Sturgeon (Huso huso), lives in the Caspian Sea and the Black Sea and spawns in the rivers flowing into them. The occurrences in the Sea of Azov (tributary of the Black Sea) and the Adriatic Sea are extinct. Beluga sturgeons have a length of 180 – 250 cm, but can also grow up to 600 cm long, weigh over a ton and live up to 100 years. Reports from the 19th century even give lengths of up to eight metres.

The Beluga Sturgeon has the typical elongated shape of sturgeons with five rows of bony shields, but is stockier. On the snout of the Beluga Sturgeon are sensory organs (electroreceptors) that can detect even weak electrical fields and fine temperature differences and thus locate prey.

Young Beluga Sturgeons wrens spend the first years of their lives in fresh water and then migrate to the sea. After reaching sexual maturity at 15-20 years of age, the fish migrate back to freshwater to spawn. The Beluga Sturgeon spawns at intervals of two to four years, i.e. not every year. Spawning migrations usually begin in autumn, and the actual spawning process takes place between April and June. Spawning is triggered by flood events over a longer period of time. The 4-8 million eggs are deposited over gravelly to stony substrates at a water depth of 3 – 20 m, at water temperatures of approx. 9 – 17 °C and a flow velocity of 1 – 2 m/s. The number of fish caught indicates that the spawning process is triggered by flood events over a longer period of time.

Catch figures indicate that populations have declined by about 90 % in the last three generations. Due to its high value as an edible fish and caviar supplier, the Sturgeons population in various waters is supported by stocking with juvenile fish. In the Volga, the species probably only exists because of this stocking, as the spawning grounds in the Volga were destroyed or made inaccessible for the animals by the construction of the Volgograd reservoir. The embankments of the Danube have long been an impenetrable barrier.

The Beluga Sturgeons is listed in the Red List International Union for Conservation of Nature and Natural Resources (IUCN) as a “globally threatened species”. It is feared that a species that has lived on the planet since the time of the dinosaurs will not survive the age of man.

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Image: By Максим Яковлєв – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=67084661