Disease scare threatens Hampshire’s last native crayfish population
24 October 2011
A suspected outbreak of the disease ‘crayfish plague’ on the upper River Itchen evoked widespread alarm amongst Trust staff and statutory partners. Though it proved to be a false alarm, it is a stiff reminder of how vulnerable our last remaining native white-clawed population is, and emphasises the importance of all river user taking appropriate bio-security measures.
The white-clawed crayfish is the UK’s only native species of crayfish, and the upper reaches of the River Itchen supports Hampshire’s last remaining viable (breeding) population. This very rare and intriguing native species was lost from virtually all of Hampshire’s rivers, including the middle and lower Itchen, during the 1980’s and 1990’s with outbreaks of the disease crayfish plague the key suspect in most cases.
‘Crayfish plague’ is a fungal-like disease that is carried by non-native species of crayfish from North America, such as the signal crayfish, the effects of which they have evolved a resistance. However, if the spores of this disease enter a watercourse supporting white-clawed crayfish, it will cause mass mortality of our native species. The potency of the disease is exacerbated by the fact that, under the right conditions, it can live for over two weeks without a crayfish host and can even be transferred between rivers, lakes and ponds on wet or even muddy equipment such as boots, fishing nets and traps.
During joint Wildlife Trust and Environment Agency monitoring in early September, a portion of the native crayfish population was observed to be behaving strangely (i.e. highly active and moving around during the day*), sparking fears that ‘crayfish plague’ had been transmitted to the upper Itchen. Swift action was taken by the Trust and Environment Agency to seek confirmation of this and to ensure that none of our activities increased the risk of spreading a potentially devastating disease outbreak. Samples were sent to the Centre for Environment, Fisheries & Aquaculture Science (Cefas) and were promptly analysed for this disease.
Thankfully the results proved negative for ‘crayfish plague’, and the Wildlife Trust and Environment Agency are continuing to monitor the population in an effort to determine what is causing this unexplained behaviour.
However, what cannot be ignored is that a positive result would have been catastrophic and is likely to have resulted in the total loss of this ‘keystone’ native freshwater species from Hampshire. It is a timely reminder to us all, emphasising that all river user must take appropriate bio-security measures when visiting any of Hampshire’s very special rivers.
* white-clawed crayfish are primarily nocturnal and spend the day sheltering under rocks, in burrows or amongst vegetation, coming out to feed at night.
