Spotlight on hydro as barriers block salmon

Hydro-electrics at Murrays Cauld near Selkirk. Photograph: Stuart Cobley

Matthew Newton, a scientist at Glasgow University, used state-of-the-art radio tagging technology in a two-year study of salmon in Scotland as they migrate upriver to breed. He discovered that barriers such as weirs and dams can delay a fish’s progress for up to a month, and in some cases prove uncrossable. He found that 10 per cent of fish failed to pass each barrier.

The environmental and evolutionary biology PhD student will publish the results next year in his thesis.

He says salmon and trout populations in rivers with several of these hurdles, sometimes as many as eight, could be under serious threat.

The 26-year-old, who lives in Stirling, also warns that small-scale hydro-electric schemes that utilise existing weirs could pose a further threat by impacting on water levels and flow rates near the barriers.

Fish passes installed at large-scale hydro schemes have proved effective, but Newton fears smaller installations could stop them in their tracks.

“I’m focusing on the smaller-scale installations, run-of-river schemes and barriers of under 5m in height,” he said. “We don’t really know what effect these newish, small-scale schemes are having. This is one of the only studies.”

Most barriers have fish passes or ladders built in, but Newton’s studies showed they often don’t work as well as they should and salmon will actually jump across the barrier itself or even swim up the face of a weir if conditions allow.

But he found that fish that were unable to cross were spending up to a month moving up and downstream before finding their way through.

“The longer a fish is delayed the more swimming it’s doing,” he said. “If they get to spawning grounds and don’t have any energy left they’re not going to be able to spawn, and that can knock-on in populations. Also some fish will never get across these barriers, so it’s ultimately reducing the number of fish that can get to spawning grounds.

“At each site there will be a window of opportunity for fish to pass, where the flow is not too high and not too low. If it’s too low, it’s not deep enough. And if it’s too high, generally the velocity of the water is too high and the fish are physically not able to swim against it.

“If you have hydro-power abstractions that are actually taking water away from this weir then generally flows aren’t going to occur that would allow the fish to get across naturally.”

Sparked by the drive for more sustainable energy, about 500 licences for hydro schemes of all sizes have been granted by the Scottish Environment Protection Agency (Sepa), with a further 32 under consideration.

Newton said further studies into their impact were necessary. “There is a huge requirement to understand fish movements at barriers such as these in order to provide good management decisions that enable fish passage along with hydro-power production.”

A Sepa spokesman said that all small-scale hydro applications had to make provision for the free movement of fish. The agency has also made £8 million available through the Water Environment Fund to help clear redundant man-made barriers, with access for fish restored to more than 3,000km of Scotland’s rivers in the past six years.

Salmon and sea trout angling is worth £73 million a year to the Scottish economy.

Dr Alan Wells, policy and planning director at the Association of Salmon Fishery Boards, said there had been a downward trend since the 1960s in the survival of Atlantic salmon and so the new research was a cause for concern.

“Any reduction in the number of fish reaching spawning grounds resulting from small-scale hydro schemes must be taken extremely seriously by fishery managers and regulators,” he said.