The stream-walking volunteers have had to be mindful of
aliens: and no that doesn't mean the latest Doctor Who monster, but an alien
species of crayfish that can cause problems for the native crayfish in the
streams of the Wyre Forest.
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| Atlantic Stream or white-clawed crayfish, courtesy Rosemary Winnall |
The Atlantic Stream or white-clawed crayfish (Austropotamobius pallipes) is the native
species of crayfish found in the British Isles. There has been a significant decline in
native crayfish populations across England and Wales in recent years, and this
has also been the case locally too. Much has been written about the local
problem (see links below), and a major culprit for the decline is likely to be
the invasion of local streams by an alien, or non-native crayfish, in
particular the American Signal crayfish (Pacifastacus lenuisculus) which carries a
disease (a fungal pathogen) which attacks the native crayfish.
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| American signal crayfish, courtesy Rosemary Winnall |
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| American Signal Crayfish, courtesy Rosemary Winnall |
Volunteers have been advised to take precautions to avoid
the spread of the pathogen. As the alien crayfish is found mainly in some of the
tributaries, the Dowles and the Baveney Brooks, one of the precautions has been
to stream-walk each brook and tributary separately to avoid stream-hopping. Stream-walking
was, therefore, carried out separately by different volunteers for each
watercourse. The fungal pathogen does not survive for long outside water, so
washing waders and leaving them to dry before re-visiting any of the streams
was also a precaution. Obviously, there is the potential for contamination to
be innocently spread by members of the general public, but at least for the
purposes of the survey, we can keep this likelihood to a minimum.
Our last post showed the photograph of the claws of an American
Signal crayfish on the Baveney Brook (the remains, possibly, of an otter meal)
taken by volunteer Terry, showing that the alien crayfish still lurk in that
stream. Note the larger, broader claws, which are one of the traits differentiating the Signal crayfish from the native crayfish.
Thanks are due to Dr Graham Hill of Hills Ecology Ltd
and Cody Levine of Worcestershire County Council for their advice. All images
are courtesy of Rosemary Winnall of Wyre Forest Study Group.
By Liz Pearson
lpearson@worcestershire.gov.uk; Google+
By Liz Pearson
lpearson@worcestershire.gov.uk; Google+
Links
