The Wensum roach has been in decline over the past few decades.
Scientific research into Wensum roach decline shows lack of food is to blame.
River Wensum roach are living on 'starvation rations.’
That’s the conclusion of Environment Agency scientists following research into the decline of the species once prevalent on the Norfolk waterway.
The upper Wesnum is famous for both the quantity and quality of its roach. However, over the past few decades both the general number and the specimen sizes of the species on the river have fallen dramatically.
Often blamed on over predation by cormorants, otters amonst other species, following scientific research the blame for the roach's decline has now been blamed on man-made attempts to actually improve the quality of the waterway. The process of phosphorous stripping being found to be the cause of a lack of zoo plankton on the Wensum, a key food source for roach and a lack of which has left the species wasting away through a lack of nutrition.
“Roach growth rates in the Wensum were significantly higher prior to phosphate stripping," said EA fish biologist Helen Beardsley studying the Wensum.
“Phosphate is responsible for algal productivity within rivers. By removing this to improve water quality the food source for these fish is also removed.
“Where Zoo Plankton is minimal, roach have been forced to consume algae, proven to be less nutritious particularly for juveniles requiring vital growth before the onset of colder water temperatures. By removing phosphate to improve water quality the food source of these fish is thus removed and you can see why roach have declined in growth and quality since the onset of phosphate stripping,” she added.
What is phosphate stripping? Phosphates are produced in large quantities by human waste and can be harmful to the environment. Sewerage works along the Wensum have tried to reduce the amount of phosphate that they allow out into the water system through the process of phosphate stripping which sees chemicals applied to waste matter removing up to 95percent of phosphates present.