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Crayfish Invaders and Climate Change Threaten the River Usk

Posted on: Wednesday, 19 December 2007, 18:00 CST

By Steve Dube

Foreign invaders and climate change are posing the biggest threats to the health of the river Usk. A two-day conference organised by the Countryside Council for Wales at Abergavenny last month was told that 11 invasive species now affect the river while climate change could affect the quality and quantity of the water, which supplies much of South East Wales including Cardiff and Newport.

The worst invaders, according to Tristan Hatton-Ellis, CCW's senior freshwater ecologist, are signal crayfish and giant hogweed.

Systematic annual spraying of hogweed in a co-ordinated assault involving local landowners, the Environment Agency, Keep Wales Tidy and local authorities is beginning to have some effect.

But Mr Hatton-Ellis said the effect of the signal crayfish on the native species could be compared to the devastation inflicted on the native red squirrel by the North American grey.

"The signal crayfish is an escape from commercial aquaculture," he said.

"It's big and aggressive and eats smaller crayfish and has brought crayfish plague, which kills the native species."

The answer lies in an eradication programme using trapping and pesticides, but the problem is extensive and persistent.

Other threats include the impacts of barriers on migrating fish like the allis and twaite shad and silt runoff from nearby land, which affects the quality of the water.

The shad species is only found in Wales in the Usk, Wye, Towy and one tributary of the Severn. Unlike the salmon, it cannot leap any obstacle, so is threatened by any barrier placed in the river.

Water quality was affected by the wet summer, which increased the run-off of silt and pollutants.

This problem may get worse if climate change brings stormier weather, more farm land is used for arable crops and the cover of concrete and tarmac is extended by development along the M4 corridor.

On the other hand, periods of drought will threaten water supplies and hit aquatic life through lower oxygen levels.

"Climate change is always the bogeyman," said Mr Hatton-Ellis.

"The problem is that water for Cardiff and Newport comes from the Usk, and on the whole the environmental impacts are not too serious.

"But development along the M4 corridor will increase pressure on the river and in future we may not have enough water for both wildlife and people, especially in summer."

Mr Hatton-Ellis said the Usk was in a relatively good condition, especially in terms of water quality and river habitats.

This reflects the river's international importance for conservation - and highlighted the need to invest in resources and for organisations to work together to secure a healthy future.

The conference considered a wide range of issues relating to the river and considered presentations from freshwater scientists, the Welsh Assembly Government, Environment Agency Wales, Dr Cymru and the Wye and Usk Foundation.

A short report on the conference findings will be published by CCW in the new year. The report will use the key issues to make recommendations to the Severn River Basin District Liaison Panel - the group responsible for the strategic management of the Usk.

The river is home to several threatened species of fish, including Atlantic salmon, shad, bullhead and lampreys. Animals such as otters and bats also rely on the river for food and shelter.

The Usk is considered of national and European importance for wildlife and is a designated Site of Special Scientific Interest and Special Area of Conservation - the highest level of environment protection in Europe.: Home-produced fertiliser has economic as well as environmental benefits:Farmers are the common target when the subject of river pollution comes to attention. Localised problems of sheep dip and silt run-off from arable land continues to affect the Usk, but no more than the effects of an urban landscape.

Oil, diesel and other pollutants and debris gets flushed into the river by heavy rains hitting concrete and tarmac. Little can be done about the urban pollution but farming is another matter.

Connor Docherty, the CCW's soil and forestry policy adviser, said some upstream areas of the Usk are affected by sheep dip and nitrogen.

"We're not trying to blame anyone for the pollution but we try to work out where it's coming from and see whether we can work with farmers rather than take a regulatory approach," he said.

Sometimes this could involve an element of training or advice in the farmer's own interests. Using more home produced fertiliser in the right quantities has economic as well as environmental benefits.

"The essence of nutrient management is to maximise the use of slurry by putting it on at the right times and in the right quantity," said Mr Docherty.

"If you do that you should be able to do away with inorganic compound fertilisers and get away with a top dressing of nitrogen."

Mr Docherty said the CCW approach was "to win hearts and minds and make farmers aware of what happens when little things go wrong". He said, "The River Usk is in good shape but there are localised issues that have to be addressed and we want to engage with farmers to put them right."

Source: Western Mail

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