The last stand of Wensleydale’s crayfish?
by Martin Hammond
The White-clawed Crayfish, a mini-lobster found in clean, hard-water rivers and lakes, is considered to be Britain’s only native crayfish. However, like many edible creatures, its distribution is not entirely natural. Aquaculture was important to medieval monasteries, who took the ‘fish on Fridays’ rule seriously: by historical tradition, Jesus was believed to have died on a Friday, and abstaining from meat was a way of honouring His sacrifice. Instead, fish was eaten, and crayfish were deemed to be honorary fish. (The Salmon and Freshwater Fisheries Act of 1975 continues to govern the trapping of crayfish!) It’s quite likely, then, that some White-clawed Crayfish populations, especially those in isolated lakes, were the result of monastic introductions.
In later times, crayfish continued to be introduced either as a human food source or to supplement the diet of Brown Trout. In North Yorkshire, we know that White-clawed Crayfish was introduced to the River Ure by Christopher Metcalfe of Nappa Hall at Askrigg in the 16th Century. An early edition of William Camden’s Britannia states that the Ure downstream of Askrigg held an “abundance of crayfishes, ever since C. Metcalfe, within the memory of this age, brought that sort of fish hither from the south parts of England”. A later footnote, however, adds that “Sir Christopher Metcalfe might have had a stock of crayfish nearer home; for in the county of Westmorland, the rivers Kent, Lowther, and others, are plentifully stocked with them”.
The naturalist Charles Fothergill provided a rare account of the Wensleydale crayfish fishery in his diary of 1805[1]:
“The crayfish is very numerous in this part of the country… great numbers are annually caught in the streams and Semer water. The cray-fishers principally live at Baynbridge, their mode of catching them is as follows: a stick of about 2 yards long with a line of common pack thread of the same length: the bait is usually dog’s flesh tho’ beast-livers are sometimes used; dog’s flesh is not said to be used because the fish prefer it but because it is the cheapest; of this flesh a lump of about half a pound weight that it may last long is fastened to the length of each line. Several rods and lines being thus prepared, they are set in the haunts of the fish which are generally deep places, always amongst stones or hollow banks, at about 5 or 6 yards distance from each other.”
Fothergill went on to describe how the fisherman would return to raise the line and catch crayfish which had taken the bait with a net, “not unfrequently finding 20 hanging to it at a time”. The live crayfish would then be placed in a chest with water flowing through it until there were enough to take to market. Crayfish harvesting took place in August and September, with several hundred sometimes taken in a night. He also noted that crayfish were a favourite food of Otters.
White-clawed Crayfish remained widespread in North Yorkshire’s limestone rivers well into the 20th century; crayfish need plentiful calcium to form their exoskeletons, so are generally absent from soft-water, acidic catchments such as the River Esk on the North York Moors. However, population decline became increasingly evident. In the lowlands, river engineering must have taken its toll by converting many watercourses into uniform, canal-like channels lacking features like submerged tree roots and undercut banks which crayfish (and many other river species) need for food and shelter. Siltation from arable farming and forestry clear-fells must also have had an impact, alongside pollution and pesticide run-off.
A further blow was the introduction of Signal Crayfish from North America in the 1980s. This more robust species is better suited to captive rearing for the restaurant trade and began to be stocked in fish farms. It is a great escape artist, able to walk considerable distances overland, and feral populations established quickly. As well as being more competitive, Signal Crayfish hosts a fungal pathogen, Aphanomyces astaci, more commonly referred to as crayfish plague. The Signal itself is resistant to disease but it’s 100% lethal to its White-clawed relative.
As a result, the White-clawed Crayfish is rapidly disappearing from its former strongholds in the rivers draining the Yorkshire Dales. Signal Crayfish have been established in the lower reaches of the River Ure for some time and it has replaced White-clawed Crayfish in most of the Aire, Wharfe, Nidd and Tees catchments.
Nonetheless, it was hoped that natural barriers such as Aysgarth Falls would prevent its spread upstream into Wensleydale. Sadly, monitoring by the Environment Agency has shown that this is no longer the case and crayfish plague has now reached the uppermost reaches of the river, as the map below shows.
Environment Agency map showing the upstream spread of crayfish plague
A few isolated populations of White-clawed Crayfish survive in Upper Wensleydale tributaries, shown by green dots on the map above. Spores of crayfish plague can easily be spread on damp footwear, equipment, vehicle tyres and fishing or boating gear. If our native crayfish is to stand any chance of survival, walkers, naturalists, anglers and canoeists all need to help by following Environment Agency guidance:
· Please avoid contact with water if possible in the Upper Ure tributaries
· If contact with water can’t be avoided, follow the ‘Check, Clean, Dry’ protocol rigorously http://www.nonnativespecies.org/checkcleandry/ · Don’t move from one watercourse to another without doing so[1] The diary of Charles Fothergill, 1805. Yorkshire Archaeological Society, 1984.