Sturgeon - the Danube's endangered giant
The world's biggest freshwater fish, the beluga or also known as sturgeon (Huso huso) is an anadromous type of fish. It can be found in the Caspian and Black Sea basin, and formerly in the Adriatic Sea. Beluga is not only the biggest freshwater fish, but it is the third largest living species of bony fish. Their size can rival that of the ocean sunfish and the great white shark.
(Photo: Wikipedia: Huso_huso_adult_juvenile)
The sturgeon undergoes a spectacular change during its growth. As juveniles, they are slender in body and have a narrow head with a thin and pointed snout. Their back is dark grey or black and the belly is white. The adult specimens are massive in size, spindle-shaped, and humpbacked. The head is large, and the snout becomes quite short. Their coloring becomes blue grey or dark brown with silver or gray flanks, the belly stays white.
They are anadromous, and they adopted a two-stage migration strategy. Sturgeons migrate from the Black Sea up the Danube as far as Germany, meaning that they enter the river in fall and stay over the winter. nowadays, only a few wintering and spawning grounds are known. The sturgeon matures quite slowly. The male reaches sexual maturity at 12-16 years of age, and the females do at 16-22, and they only go to spawn every 4 to 7 years. They are extremely long lived and can reach more than 100 years. The belugas are predatory fish and the very large ones even prey on aquatic birds and young seals.
The largest recorded catch was a female one, with the size of 7.2 m and 1.571 kg, found in Russia in 1827. These days, the mature belugas that are caught are between 142-328 cm. Females are usually bigger than males and are heavily fished for their valuable roe known as beluga caviar which is considered a delicacy. The most expensive type of caviar is the Almas (it means diamond in Russian), which comes from a very rare albino type of sturgeon. Its price can be as high as $25000 per kilo.
This extraordinary giant that outlived the dinosaurs now unfortunately faces extinction. Due to the fact that in the last 50 years their numbers significantly decreased because of over-fishing, poaching, pollution, loss of habitat, and dams that block their migration routes, out of the 27 sturgeon species that are listed in the IUCN red list, 17 are critically endangered and 4 are possibly extinct. In 2017, the WWF started a new global strategy to try and save the wild sturgeons. The program works with regions (Europe, Asia, North America) where sturgeons still live. The WWF tries to help to stop the over-exploitations, preserve the migration routes, protect and restore habitats, and create breeding centers to restock wild populations. Lets’ hope that with all these efforts this impressive fish can still survive!
Sources: https://en.wikipedia.org/wiki/Beluga_(sturgeon) , https://wwf.panda.org/wwf_news/?311090/WWF-launches-last-ditch-effort-to-save-worlds-wild-sturgeons, https://danube-sturgeons.org/sturgeon/beluga-sturgeon/ ,https://www.azureazure.com/gastronomy/food-drink/most-expensive-caviar/, https://www.icpdr.org/main/publications/cut-river-reconnecting-sturgeon-migration-routes
(Cover photo: wikipedia - Білуга_(Huso_huso) )