Global warming threatens the Arctic charr
22 January 2010, by Sara Coelho
Arctic charr populations are falling throughout Britain and although part of the decline is due to specific local factors, scientists are now suggesting that global warming may also play a role. This is the first time that climate change has been linked to the decline of a fish species in Britain.
The Arctic charr (Salvelinus alpinus) is a trout-like cold-water fish common in Northern Europe, Russia and Canada. In Britain, already at the southernmost end of the species' distribution, they are restricted to deep lakes and lochs where water temperature stays under 15°C even in summer.
'They need cold water to survive and there are reasons to believe that climate change has a negative impact on this species,' says Dr Ian Winfield, from the Centre of Ecology & Hydrology, who compiled data surveyed in 11 locations in the Shetlands, Scotland, England and North Wales.
'This is the first time we see evidence of negative effects of climate change on a UK fish species.'
Dr Ian Winfield,
Centre of Ecology & Hydrology
The team found that since 1990, ten of the 11 populations of Arctic charr have declined significantly. The only increase occurred in the Shetlands' Loch of Girlsta, the northernmost surveyed site.
The decline of the Arctic charr is concerning as 'the species is listed as priority in the UK Biodiversity Action Plan and is already being affected by a wide range of problems,' he adds.
The species is particularly vulnerable to lake eutrophication, or undue fertilisation, that stimulates algal growth. 'The algae alone are not a problem,' says Winfield. 'But as they rot, the decomposition process consumes too much oxygen and the charr need well-oxygenated waters to survive.'
Other populations are threatened by competition with introduced fish such as the roach or an excessive number of cormorants that feed on charr.
But such local environmental factors alone do not explain the drop in Arctic charr numbers reported last week in Hydrobiologia. To figure out the possible effects of global warming on the species's numbers, Winfield and colleagues assigned an index of vulnerability to climate change to all surveyed locations. The vulnerability ranking depends on the lake's latitude, altitude and mean depth.
'The index was meant to predict how much water temperature of a given site is likely to change with global warming,' explains Winfield. Southern lakes at low altitude and with shallow waters have a high vulnerability and are more likely to get warmer than deep, mountainous lakes in the north.
Winfield found that the locations more vulnerable to climate change were also the sites where the Arctic charr declined the most. 'The index correlates very well with the population decrease observed since 1990,' says Winfield. This means that rising water temperatures might be playing a role in the species decline.
'This is the first time we see evidence of negative effects of climate change on a UK fish species,' he says, adding that more work needs to be done to understand the precise mechanisms involved in the decline.
The research was done in collaboration with the Environment Agency and Scottish Natural Heritage.
I.J. Winfield, J. Hateley, J.M. Fletcher, J.B. James, C.W. Bean and P. Clabburn. Population trends of Arctic charr (Salvelinus alpinus) in the UK: assessing the evidence for a widespread decline in response to climate change. Hydrobiologia. Published online: 11 January 2010. doi: 10.1007/s10750-009-0078-1
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