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Rivers tot up 11 new species as aliens spread their fins

Posted on 17/05/17 in News

By Lewis Smith

UK and European lakes and rivers boast 11 more fish species than they did 170 years ago, despite 15 going extinct.

The introduction of 26 species of exotic fish has more than compensated for the extinctions - at least in terms of the number of species.

Among the species believed to have gone extinct are the houting, which was once native to UK estuaries and other parts of northern Europe.

However, transfers of native European species between river systems has wrought a far bigger change on the make-up of lakes and rivers than exotics.

“Our study showed that the European freshwater fish fauna has changed profoundly since 1840,” reported the research team.

Every single one of Europe’s 251 main river basins has at least one more species of fish living in them than since 1840, and the rainbow trout is found in all of them. It was originally native to North America and Asia.

On average, each river basin holds an extra 5.7 species of fish compared to what was there 170 years ago and some have as many as 26. In total, 77 native species have increased their range.

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Among the winners are the European carp which has spread from 33 to 151 river basins, and the Prussian carp which was originally in 33 river systems but is now in 151. European flounder and European perch have also expanded their range.

Alien invaders include the largemouth bass, native to the US but now in 47 European river systems, and the eastern mosquitofish, also from the US and now in 61 river basins. Another is the so-iuy mullet , originally from China and now in 27 river basins.

The total number of extra species hides an even more radical change in the make-up of European river ecosystems because it is a net gain, with several species being lost.

Overall, 41 species have suffered a decrease in their range, with twelve restricted to less than half the area they were in 170 years ago.

Losers include the European sturgeon, the Russian sturgeon and the beluga, each now critically endangered, while the Gulf sturgeon is extinct in European waters.

Up to half of all fish species are under threat, with “a particularly high proportion of threatened species in Southern Europe” where the number of introduced species is highest.

Researchers assessing the make-up of freshwater habitats across Europe found that all 251 catchment areas hosted at least one introduced exotic species and that 76 per cent had at least one species translocated from another part of the continent.

They calculated that the combination of some fish being moved from one area to another, other types being driven into local or regional extinction, and exotics from other parts of the world being introduced, meant that 20 per cent of each river system had been changed.

“Species turnover was much higher than the net gain indicates. On average, one fifth of the historic assemblages became reshuffled,” the researchers reported.

Of the 541 species of freshwater fish recorded in Europe, 468 are found in the 251 major river basins, according to the German study published in the Journal of Biogeography.

While the total number of species has increased, there is “concern” that Europe’s freshwater ecosystems are increasingly coming to be copies of each other, rather than displaying local and regional differences.

Dr Nike Sommerwerk said: “Such studies are important in identifying and implementing appropriate management strategies for species protection and biodiversity management.”

Photo: rainbow trout are now found across Europe. Credit: Ken Hammond / USDA, via Wikimedia Commons