Category Archives: Rivers of Britain

Cleaner rivers in the UK

Otters, water voles and fish are all benefitting from the improved quality of the UK’s waterways, now described as the cleanest since the industrial revolution.  Since almost disappearing from the wild in the 1970s, otters are thriving, particularly in the south west of England, Cumbria and Northumberland.  The population of water voles, highly precarious  in the 1990s, is also beginning to recover.   The good results of stricter pollution controls and extensive conservation work are set to continue in the new year with the introduction of new European water quality directives.  Guardian

Mystery of vanishing eels

The eel population of the Thames has dropped by 98% in 5 years and conservationists can only speculate why. The Thames eels (Anguilla anguilla) are born 4000 miles away in the Sargasso Sea, located in the North Atlantic Ocean, from where they migrate to British fresh waters.  After up to 20 years they return to their breeding grounds to spawn and die. To make these long journeys the eels rely on ocean currents, which are susceptible to changes in temperature.

Disease and pollution could also be causing problems for the eel.  Although the Thames has revived since its “biological death” in the 1950s, the river remains under heavy urban pressure.  And the Sargasso Sea, in contrast with its romantic image, suffers from a particularly high concentration of non-biodegradable plastic waste, trapped there by ocean currents.

Alien crabs on the menu

The idea of harvesting the invasive Chinese Mitten Crab, currently clogging up the Thames and rapidly spreading through Britain, is taking shape, with a conference planned for March to discuss the pros and cons.

It’s been proposed to use fyke nets, as pictured above.  But these long net tubes held open by hoops are also a very efficient means of trapping eels, now a threatened species in Europe.  Another drawback is, if the crab fishery were an economic success, people might be tempted to introduce the Mitten Crab to new rivers. As Paul Clark, marine biologist at the Natural History Museum and conference organiser, puts it:

“We are damned if we do and damned if we don’t. Mitten crabs have few natural enemies capable of reducing their numbers, but the establishment of a fishery would certainly carry risks.”

In Shanghai the Mitten Crab (Eriocheir sinensis) is a delicacy.  They are eaten steamed, as this best preserves the flavour and keeps the meat tender.

See the Independent and previous post

Plan to save British crayfish

A £210,000 breeding programme has been started to save Britain’s rare native white-clawed crayfish. The species (Austropotamobius pallipes) is in danger of being wiped out by invasive American signal crayfish, which carry a disease, crayfish plague, which is fatal to the British species. The crayfish are being bred at secret locations in the south-west of England. American crayfish were introduced in the UK twenty years ago for farming. This has since led to the disappearance of almost 95% of the native species, which faces extinction from UK waters within 30 years unless new populations can be created in safe, uncontaminated waters. The Guardian

Mitten crabs in the Thames

Chinese mitten crabs are becoming increasingly common in the River Thames and other rivers in England, having arrived in ship’s ballast from Asia. Mitten crabs cause a great deal of damage by burrowing into and destroying fragile riverbanks. They prey on other species and compete with native animals such as crayfish. Continue reading Mitten crabs in the Thames