Sturgeons are the most endangered animal group in the world. The main causes are overfishing, fragmentation of water bodies, pollution and the consequences of climate change.
08/09/2022 · News · Leibniz-Institut für Gewässerökologie und Binnenfischerei · Umweltwissenschaften · Forschungsergebnis
They have witnessed quite a few dramatic changes over the past 250 million years since their first appearance, but by now they the most threatened group of animals in the world - the sturgeons. Until recently, there were 27 species of the order Acipenseriformes, now there are only 26 since the Chinese paddlefish is considered extinct since this assessment by the International Union for Conservation of Nature (IUCN) in July this year. For the remaining sturgeon species, the situation has deteriorated significantly since the last assessment in 2010, with the change being most dramatic in Europe and Asia. The main causes are overfishing, fragmentation of water bodies, pollution and the consequences of climate change. Dr Jörn Gessner from IGB played a leading role in drawing up the IUCN Red List; he is also coordinating the reintroduction of the European sturgeon and the Atlantic sturgeon, which were formerly native to Germany.
The International Union for Conservation of Nature, or IUCN for short, is the global body for assessing the state of nature and the measures needed to protect it. It has more than 1,400 member organisations and is supported by around 15,000 experts.
On 21 July 2022, IUCN published the updated version on the status of the group of paddlefish and sturgeons (Acipenseriformes), which was prepared by representatives of the Sturgeon Specialist Group under the leadership of IGB researcher Dr Jörn Gessner and Dr Arne Ludwig from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW). "Since the last assessment in 2010, the situation has generally deteriorated. One species, the Chinese paddlefish (Psephurus gladius) is already considered extinct. Another species is only found due to stocking measures and is considered extinct in the wild. For eight species, the status is more critical than in the 2010 assessment. The status of 17 species remained unchanged critical, and the status of one species still classified as critical has improved," IGB researcher Jörn Gessner sums up the result.
Some sturgeon species only survive thanks to early conservation programmes
The Yangtze River sturgeon or Dabry sturgeon (Acipenser dabryanus) native to the Yangtze River in China, was upgraded from "Critically Endangered" to "Extinct in the Wild" because although the animals still occur in their original habitat, they only come from stocking programs and no natural reproduction has been observed in the last 20 years. Only 22 remaining individuals (11 males and 11 females) of the Chinese sturgeon (Acipenser sinensis) participated in the last recorded natural spawning event in 2015, according to a genetic study. The Ship sturgeon (Acipenser nudiventris) is one of the eight species found in Europe that used to be widespread in the Black Sea basin. Today, the species is only found in a small remnant population in Georgia and has been declared extinct in the Danube.
In general, species in North America are in a less dramatic situation. Here, conservation programmes and other management measures were initiated before many of the natural populations were threatened with extinction. But even in these cases, the status of the populations deteriorated compared to the 2010 assessment due to changes in the criteria used by the IUCN for the assessment.
In Europe, the decline is most dramatic, there are few bright spots
The new IUCN assessment shows that the situation in Europe is among the most dramatic: all eight species present are classified as "vulnerable" or "threatened with extinction". But there are also small signs of hope. The discovery of young Adriatic sturgeon (Acipenser naccarii) in a northern Italian river indicates that, after more than 30 years of relief efforts, the animals are now reproducing naturally. As a result, this species has been downgraded from "extinct in the wild" to "threatened with extinction". Also, the recent rediscovery of juveniles of the Ship sturgeon (Acipenser nudiventris) in the Rioni River in Georgia, which was previously thought to be extinct in the Black Sea basin, could enable the rescue of the Black Sea genotype of this species if timely action is taken.
Setbacks for the reintroduction in the River Elbe
The European sturgeons (Acipenser sturio) and Baltic sturgeons (Acipenser oxyrinchus) formerly native to Germany, are on the rise again in their catchment areas, but evidence of self-reproduction is still lacking here for their status to improve according to IUCN criteria. Currently, all animals in the Elbe and Oder come from stocking, but this is expected to change in the coming years when, as has already happened in the Elbe, the first returnees emerge and reproduce without human help. But even then, it will take decades until the stocks are sufficiently robust, so that relief measures such as stocking but also habitat improvements will continue to be indispensable.
This summer, for example, several specimens of the European sturgeon died in the River Elbe due to lack of oxygen. For Jörn Gessner, this was a heavy blow: "These were the first returning fish from our reintroduction project, over 1.5-meter-tall and over 10 years old, which should have produced the first generation of wild fish since 1964".
Caviar production is not the main problem at present
"The causes of the decline of sturgeon and paddlefish can all be attributed to humans, with the main causes being overfishing, river fragmentation and pollution. Overfishing used to be mainly due to hunting for caviar and is no longer the main factor," explains Jörn Gessner. Caviar, once the food of the poor and without value, became a luxury good in Western Europe in the mid-19th century. Today, sturgeon fishing is banned practically everywhere, and the approximately 500 tonnes of caviar that are legally produced worldwide every year come from farmed animals. Legal fishing is therefore no longer a threat, and the remaining poaching is limited to a few areas, where it still causes serious damage to the small remaining populations.
Sturgeon migration routes are disrupted
Today, the fragmentation of their habitats and especially of the rivers in which they are supposed to breed is the main cause for the decline of sturgeon and paddlefish. Most sturgeon species are anadromous, which means that they live as adults in coastal areas and in the sea and migrate to their native rivers to spawn. Dams, which have been built in large numbers since the 1950s, prevent their migration to historic spawning grounds and profoundly alter the ecology of rivers, severely limiting the reproduction of these species. "It is no wonder, for example, that the Chinese paddlefish became extinct, because its habitat was the Yangtze River. The course of the Yangtze was completely altered first by the Gezhouba Dam, built in 1981, and then by the gigantic Three Gorges Dam, completed in 2006. Today, more dams have been added in the middle and upper reaches of the river. These dams interrupt the migration route to the spawning grounds of this iconic species and the dams destroy their feeding grounds," says Jörn Gessner.
Water pollution has also had a negative impact on sturgeon and paddlefish, as has the introduction of alien species that in some cases compete with or displace sturgeon and paddlefish, as in the case of the European catfish (Silurus glanis) in Italy and France.