Essex Rivers Hub

On Friday we were running our annual White-clawed Crayfish training day, run by Martin Pugh who is an ecologist for EECOS, which is Essex wildlife Trust's in house ecology consultancy. Not only does this give people the opportunity to  learn more about this increasingly rare species but also gives us the opportunity to monitor how the population is faring.

During the survey of Stebbing Brook we were quite concerned when only 18 adults were found and of these 16 had White Porcelain Disease. This is not to be confused with the crayfish plaque, which is carried by invasive crayfish for which our native species has no immunity to. White Porcelain Disease is a naturally occurring disease within native crayfish population but does not exceed 10% infection rate within a healthy population. To find so many of those captured on Friday to be infected was quite alarming as was the fact that we did not find any juveniles.

Instances of White Porcelain Disease can increase in populations due to environmental stresses such as lower oxygen rates in water and reduced water quality, native crayfish are very sensitive to this. As the survey was conducted after a long period of hot weather with little rainfall, this may have been a major factor in the reduced health of the population so the rain we have just had over the last few days will help in reducing some stress to the crayfish in regards to water quality. However there maybe other factors that are contributing to the reduced health of the population so further investigation is needed.

The lack of juveniles found during the survey is another concern as those infected with White Porcelain Disease are unable to reproduce so it is possible the high rates of the disease within the population are impacting on their reproductive success. Another possiblity is that something could be causing high mortality rates within the juvenile population.

To find out more about what is happening with the last known river based population of White-clawed Crayfish in Essex, more investigation will be necessary. Martin Pugh and others at Essex Wildlife Trust will be looking further into this and working with Natural England and the Environment Agency to try and find out more and hopefully turn this around so that Stebbing Brook remains a refuge for this nationally dwindling species.

We will keep you updated on this issue as more information becomes available, in the meantime if you would like to know more about White-clawed Crayfish, please see here.

Monday 27th July 2015.

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