The conservation status of all sturgeon species in Europe has become highly critical without showing signs of recovery[1]. Researchers worry, that some species have become extinct in the wild already (e.g. Adriatic sturgeon), since there is no evidence of their spawning grounds[2]. Unrestrained commercial sturgeon fishing began in 19th century and together with our appetite for its roe and meat, it has had devastating impacts, decimating their populations to a level where every individual counts.
In a few historically important European rivers, especially in Black Sea basin (e.g. Danube, Don or Dnjeper rivers), wild reproducing populations of some sturgeon species still occur, particularly Starry sturgeon and Sterlet. However, sturgeons formely plentiful, have disappeared from the vast majority of their native locations in Europe.[3]
Common sturgeon (Acipenser sturio), the largest European species, used to range from Norway to northern Mediterranean, but today only one spawning population occurs in France, Garonne, where their reproduction was recorded in 1988 for the last time.[4] As of the last update in 2010 an estimated 20 – 750 mature individuals of Common sturgeon remained in the wild.[5]
Besides the historical burden of overexploitation, sturgeons also face other threats resulting from human activities. They repeatedly move between different habitats during their lifespan. They spend majority of their lives in river estuaries and along the sea coast in search of moluscs, small fish and crustaceans on the seabed and migrate upstream into their natal rivers to release eggs. River modifications that block or reduce access to their spawning grounds, be they water regulation, material extraction, dam construction or other encroachments into natural watercourse, influence their reproductive success. In open waters, they fall victim to bycatch, which contributes to further decline in their already small populations[6].
Attempts has been made to keep them alive in their natural habitat. Many wild sturgeons are under protection today and ban on catching and selling their products is in place. International trade of all sturgeon species has been regulated under CITES since 1998 and nearly all caviars on the market today are harvested from farmed fish.[7] However, illegal and unreported fishing still occur. For example in Danube river in Black Sea basin it can make up to 90% of sturgeon catch. Unless the fishing pressure is reduced, sturgeons will not survive in the region.[8]
Reintroduction programmes are in place or planned, too. They require a lot of effort, especially better undestanding of sturgeon´s behaviour, habits and patterns in the wild, but also development of marking and tracking techniques for evaluating survival of released fish and mastery of spawning, since wild populations are supported by artificially bred individuals.
In case of Common sturgeon, they are in progress in France and Germany. French scientists have been drawing attention to risks of sturgeon populations since 1920s. In late 1970s recovery strategy was set up by Cemagref Institute as a starting point of restoration programme. In 1995 thousands of individuals were released from stockings in France, with survival rate of 3-4%, which was considered a success. Sturgeons were more recently stocked in 2007, 2008 and 2009 and reintroduction programmes are planned for river Rhine and Rhone, too.[9]
Despite the efforts made, six out of eight European sturgeons are on the brink of extinction and 63% of all sturgeon species are listed as critically endangered worldwide. Barriers that disrupt their lifecycle persist and their monitoring is not consistent. Their recovery, if possible, will take decades, since they reach reproductive maturity quite late. Depending on sex and species, they become fertile between the ages of 10 and 26 years and most females spawn once every 4 to 9 years.[10] In the wild, we might thus lose the fish that outlasted the dinosaurs in near future.
[1,3] Pan-European action plan for Sturgeons: World Sturgeon Conservation Society and WWF; Strasbourg, 30 November 2018: http://www.sturgeon.de/images/Downloads/infos/Gesamteuropischer_Aktionsplan_fr_Stre_2018.pdf
[2,5,6] IUCN https://www.iucnredlist.org/species/230/13040963
[4,9] Acipenser sturio Recovery Research Actions in France, Patrick Williot, Eric Rochard et. al, 2009 https://www.researchgate.net/publication/227278643_Acipenser_sturioRecovery_Research_Actions_in_France
[7] The Caviar Market: Production, trade and consumption in and outside of EU, EUMOFA, last update 2018 https://www.eumofa.eu/documents/20178/84590/The+caviar+market_EU.pdf
[8] https://danube-sturgeons.org/danube-sturgeons/overfishing-the-caviar-trade/
[10] Sturgeons of the NW Black Sea and lower Danube river countries, Radu Suciu 2008 https://cites.org/sites/default/files/ndf_material/WG8-CS5.pdf