Prolonged drought followed by extreme flooding could be responsible for the decline in salmon populations recorded by scientists.
The Game & Wildlife Conservation Trust (GWCT) has been monitoring Atlantic salmon populations on the River Frome for the past 40 years. Scientists have found an encouraging upturn in wild salmon stocks over the past few years, but say there is now a prospect of a severe decline in the population.
Dr Anton Ibbotson, from the GWCT’s Salmon & Trout Research Centre on the River Frome, said: “Unfortunately, the measured population size ofRiver Frome juvenile salmon in 2011 was roughly half the size of recent years, falling from 130,000 in 2010 to 64,000 in 2011; thereby reversing a recovery that had been developing over several years.
“The size of the 2012 smolt run was estimated at fewer than 7,000 fish in comparison to runs that have reached around 13,000 in recent times. This will undoubtedly have a major consequence for adult salmon returning to the River Frome and other rivers that have experienced similar conditions in the next few years.
“The impact of drought in 2011 resulted in a depleted population of juvenile salmon most likely because of a reduction in habitat. Our estimate of the number of smolts leaving the river in 2012 was unusually low and so we are anticipating a significant drop in the numbers of returning adults in 2013 and 2014.
“This has now been compounded by the extreme flooding we’ve seen since last spring and we have some evidence that the juvenile population for 2012 is also depleted. This will have ‘knock-on’ effects for the smolt output in 2013 and returns of adult salmon through to 2015.”
The charity believes the situation will have been replicated at other rivers around the South and South West of England, plus parts of Wales.