Salmon and Trout Facing Extinction as Our Rivers Warm Up; Cardiff Research Highlights Rapid Fall in Stocks

Article excerpt

Byline: Sally Williams

CLIMATE change could wipe out salmon and trout stocks in Welsh rivers over the coming decades, academics have warned.

New evidence from Cardiff University shows that warm and dry summers that reduce water levels in Welsh rivers could be a major factor in the rapid decline of both species over the past 25 years.

Professor Steve Ormerod and colleagues from the Cardiff School of Biosciences who studied populations of young salmon and trout in the RiverWye, said the populations have fallen dramatically, putting both species at risk.

They found salmon numbers fell by 50% and trout numbers by 67% between 1985 and 2004 - even though the river itself became cleaner.

Pollution, habitat loss and over-fishing had been blamed for declines in the past, but Professor Ormerod said the fish were actually hit hardest following hot, dry summers such as 1990, 2000 and 2003.

"The results suggest that warmer water and lower river levels combine to affect both species," he said.

"As both trout and salmon favour cool water, they face potentially major problems if climate warming continues as expected in the next two to three decades.

"The comparison between trout and salmon is important because, unlike salmon, trout from theWye never migrate to the sea.

"Only factors affecting the River Wye can therefore explain their decline.

"If unchecked, the impact of climate change could lead to the loss of salmon and trout from rivers in the South-West, where they already face problems from being on the edge of their range."

The Cardiff team used data on fish population collected each year by the Environment Agency at 55 locations spread throughout the River Wye.

Stream temperatures increased over the study period by 0.5-0.7C in summer and 0.7-1C in winter.

The team said water temperature is known to affect growth and susceptibility to disease in these fish, while lower water levels restrict their access to cooler habitats. …