The beluga sturgeon. Not only is it one of the rarest fish in the world but it is also one of the largest. These fish can live for a staggeringly long time which enables them to reach such large sizes. However, demand for their caviar has led to them being driven to near extinction, and their future is not the brightest.
Taxonomy and Evolution
Beluga sturgeon, not to be confused with the adorable white beluga whale, have the scientific name Huso huso. They are the only member of their genus alongside the other impressively large kaluga sturgeon. Beluga are, of course, sturgeons which belong to the order Acipenseriformes which also includes the paddlefish. This is an old order of fish dating back to the Jurassic period, although sturgeons appear in the fossil record during the Late Cretaceous. Huso is not nearly that old with the oldest fossils belong to the genus dating to around 5 million years ago.
Biology and Behaviour
I cannot overstate how big beluga sturgeon are. If we include all fish then belugas are in the top ten, but if we only include the bony fish (so discounting the sharks and rays) then they are the second largest fish after the ocean sunfish. This still comes with a caveat. As belugas grow very slowly and they have been so thoroughly exploited belugas have not reached their largest sizes for a very long time. The largest ever found was in the Volga river all the way back in 1827 which was a female that reached a staggering 7.2 metres (23.7 feet) and a weight of 1,571 kilograms (3,463 pounds)! Historical sources from the 1400s regularly described sturgeon reaching 6 metres but that is sadly something of the past. The largest belugas of today reach just over 3 metres (10 ft) and 264 kilograms (582 pounds). Female belugas are larger than the males and this is largely how you can tell the difference between male and female belugas.
Belugas have the ability to reach a century in age, but none have managed to reach that age for a very long time with most being poached by their fifties. Belugas swim upriver to spawn where the species is divided between those who spawn in the spring and those who spawn in the autumn. Young belugas will stay in rivers until they reach between 6 and 11 centimetres before they migrate to the seas travelling an incredible 24 kilometres a day. Growing slowly it takes about four years for belugas to reach a metre in length. However, they do not become sexually mature until they reach 10 years for males and 15 for females, although some can take until 25 years for sturgeon to become sexually mature. They do not spawn every year, sometimes spawning every four years, and like many fish there is no parental care for their eggs. Sturgeons change form as they age. Babies and juveniles look like mini versions of the adults with a spindle-shaped body, five rows of bony scutes, and a long, slightly curved, snout ending in four barbels a bit like a catfish. These barbels are used for sensory purposes – helping sturgeons navigate and hunt in murky river waters. The largest and oldest sturgeons look incredibly different. The barbels disappear and the head effectively becomes one large mouth. Sadly these truly giant belugas have not been seen for a good century due to human exploitation.
Distribution and Habitat
Belugas are relatively unique among fish as they can live in both saltwater and freshwater, and can easily navigate from one type of water to another. They can even live in polluted waters, but they do show signs of stress in polluted water so it is not a healthy life. Belugas are found in the Black Sea, Sea of Azov, and the Caspian Sea with them moving into the rivers that flow into those seas, mainly the Ural and Volga rivers. In the past they had a much wider range being found in many more rivers and also the Adriatic Sea. Just over a century ago they could follow the Danube up through to Austria and Hungary, and the Volga all the way into central Russia. The rivers of Russia, Azerbaijan, Kazakhstan, Turkmenistan, Iran, Turkey, Bulgaria, and Romania all have belugas, but this is a fraction of a much wider range.
Diet and Predators
Belugas are not only predators but top predators with them inhabiting the same niche that seals and otters hold in other Eurasian freshwater bodies. As belugas age their diet changes moving from invertebrates to fish. Starting off with crabs and other small crustaceans as they get larger they move onto squid, cuttlefish, and fish. Larger sturgeons have been seen eating smaller sturgeons – both fellow belugas and other species of sturgeon. Of course the largest sturgeons have no natural predators but smaller ones can be hunted by a wide range of animals including larger sturgeons, catfish, pike, ospreys, seals, otters, and eagles.
Conservation and Threats
As mentioned throughout this post, things are not looking good for beluga sturgeons. When the IUCN last assessed the beluga sturgeon in 2019 they gave it a ranking of ‘Critically Endangered’ meaning there is a real possibility that they could go extinct in the foreseeable future. Part of this is the building of dams which disrupted their migration routes and has actually made the fish stressed by the disrupted river currents. However, the biggest reason why they have become so rare is because of exploitation, primarily for caviar. Beluga caviar is one of the most luxurious caviars in the world, but belugas have to be killed in order to get this. As belugas take over a decade to reach maturity caviar production can easily wipe out a population. It is now illegal to trade beluga caviar that is not produced from a farm, but it has not stopped poaching. Following the collapse of the Soviet Union efficient conservation methods for belugas collapsed. The demographic disaster of the USSR’s collapse forced more communities to resort to poaching to survive directly impacting belugas. There have been some attempts to conserve belugas. In 2020 7,000 captive-bred sturgeons were released into the Danube with the hope that these six month old sturgeons would help re-establish the population in the Danube. Whether this will help, time can only tell.
Bibliography:
- Joseph Nelson, Terry Grande, and Mark V.H. Wilson, Fishes of the World, Fifth Edition, (Hoboken, NJ: Wiley, 2016)
- ‘Thousands of Critically Endangered Beluga Sturgeon Released into the Danube’, WWF Blog, (29/06/2020), [Accessed 05/04/2024]
- J. Gessner, M. Chebanov, and J. Freyhof, ‘Huso huso’, IUCN Red List, (2022), [Accessed 05/04/2024]
- Elisa Boscari, Ilaria A. M. Marino, Chiara Caruso, Jörn Gessner, Martina Lari, Nikolai Mugue, Anna Barmintseva, Radu Suciu, Dalia Onara, Lorenzo Zane, and Leonardo Congiu, ‘Defining criteria for the reintroduction of locally extinct populations based on contemporary and ancient genetic diversity: The case of the Adriatic Beluga sturgeon (Huso huso)’, Diversity and Distributions, 27:5, (2021), 816-827
- Larissa Graham and Brian Murphy, ‘The Decline of the Beluga Sturgeon: A Case Study about Fisheries Management’, Journal of Natural Resources and Life Sciences, 36, (2007), 66-75
- Prosanta Chakrabarty, ‘Huso huso‘, Animal Diversity Web, (2003), [Accessed 08/04/2024]
Lewis Twiby's Past and Present 