Aggressive “killer shrimp” that wipe out weaker native species and destroy insect populations have been spotted for the first time in UK waters.
The invasive species of freshwater shrimp, which has much larger and more powerful jaws than its British rivals, is notorious for its vicious and destructive behaviour. It kills or maims every insect it comes across, attacking even when it is not hungry and leaving its prey uneaten.
Its victims include damselflies and water boatmen, with knock-on effects for the fish that feed on them. It even attacks young fish and tends to dominate any habitat it enters.
The arrival of Dikerogammarus villosus, which originates from the region of Eastern Europe between the Black and Caspian seas, was discovered last Friday by anglers at Grafham Water reservoir in Cambridgeshire. They sent samples to the Environment Agency, which identified the species with the help of an expert in the Netherlands.
We are devastated that this shrimp has been found in Britain, and very grateful to the keen-eyed anglers who found it
The species has spread rapidly through western Europe since the early 1990s after travelling 2,000 miles up the river Danube and into the Rhine. It has altered the ecology of many rivers and lakes, wiping out native shrimp (Gammarus duebeni) and a less aggressive North American invasive species (Gammarus tigrinus).
Scientists predicted a decade ago, when the shrimp reached the Netherlands, that it would be only a matter of time before it invaded Britain.
An experiment in 2000 at Queen’s University Belfast demonstrated the lethal capacity of this tiny killing machine. It put the shrimp into aquariums with ten other species, including native shrimp, damselflies, water hoglice and fish leeches. It killed them all, with the uneaten remains found at the bottom of the tanks. Its success is partly linked to its rapid breeding and ability to withstand changes in oxygen levels, salinity and water temperature.
Biologists are testing the water at Grafham to see what action needs to be taken. Anglian Water said that the shrimp pose no risk to drinking water supplies. However, it has introduced precautionary measures for the thousands of fishermen, sailors and windsurfers who use the lake. These include requiring them to clean their equipment before it is used on any other lake or river.
The Environment Agency said that the shrimp could have arrived at Grafham in a variety of ways, including on boats and fishing equipment, during fish stocking or naturally via birds that have flown to the United Kingdom. It can be distinguished from native shrimp because it is much larger — about 30mm long — and often has striped or spotted markings.
Paul Leinster, chief executive of the Environment Agency, said: “We are devastated that this shrimp has been found in Britain, and very grateful to the keen-eyed anglers who found it.”
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