THE Environment Agency has discovered the presence of endangered native white-clawed crayfish in a stream near Ilkley.

Innovative environmental DNA testing was used to ascertain whether the species was present at Carr Beck, Burley Woodhead.

Environmental DNA testing looks for DNA from sloughed off cells of organisms present in the environment. The samples are then collected, sent off to a laboratory and tested to verify the presence or absence of crayfish in the beck system.

Since the survey confirming the presence of the native crayfish, the Environment Agency’s Fisheries Biodiversity and Geomorphology team has been monitoring the situation and identifying a suitable ark site to relocate the crayfish to if required.

An ark site is somewhere that allows a species such as white-clawed crayfish to exist in an isolated refuge site, in this case away from the dangers of non-native crayfish disease and other threats.

The survey was carried out after the Environment Agency applied to Defra for a drought order when water levels were low at the end of summer to temporarily reduce water flowing into Carr Beck from Carr Bottom Reservoir.

At this time the presence of white-clawed crayfish in the beck was uncertain, prompting the survey to be conducted.

Environment Agency officer Sue Penn said: “Now we know native white-clawed crayfish are in the beck, we will monitor the crayfish and move them to a suitable ark site, if it becomes necessary. We’re now in the process of identifying a suitable ark site.

“The reservoir was not being used by Yorkshire Water for public water supply at the time, but levels were low and there would otherwise be a risk that compensation water flow into the beck might have to stop altogether.

“Reducing the flow of water allows the compensation release to continue for longer if dry conditions continued. The drought order application was subsequently withdrawn as the reservoir refilled, due to substantial rainfall during December.

“In our application to Defra, we considered the likely effect of the reduced flow on the environment. We did not know if native crayfish were in Carr Beck, so we surveyed to find out.”