Essex Rivers Hub

Native Crayfish - Good News for Essex

Last year we reported our concerns for the only known river population of the native White-clawed Crayfish in Essex.

Last year when we carried out an annual survey we found relatively low numbers, and of those we found most had White Porcelain disease, which results in high fatality rates. We were therefore concerned for their future. Last years article can be read here.

However we have good news, this year's survey shows a healthy population with hardly any with White Porcelain disease and in fact we almost found a record breaking male who measured just over 53mm in length. The standard way to measure Crayfish is from the end of the shell covering above the tail to the end of the rostrum).

The numbers were still low and there was a gap in the age classes we found from very small ones, about 1-2 years old, and then larger ones of 4 or more years old. We hypothesise that the White Porcelain disease killed off a large number of the individuals between the 2-4 year age class, resulting in these being absent
from our survey results.

The reason for the improvement in the health of this population may be the wetter summer we have had this year, which has increase oxygen levels in the water and diluted any pollutants. Less elongated periods of hot weather has probably also helped.

We hope that the results from next years survey is just as positive, if not more so, and this population continues to hang on.

The picture is of the large male we found.

 

Wednesday 17th August 2016.

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