Dear all,
I've been away for a week or so, and missed the start of this topic.
Whilst working in the Thames Estuary from 1988-1992 we witnessed the
rise of the mitten crab from straggler to apparent breeding
population. We reported this in the Attrill & Thomas (1996) MEPS
paper that Phil Smith mentioned - we attributed the establishment of
a breeding population to low freshwater flows over that period. We
aslo published a paper with a little more detail just on the mitten
crab, but it is hidden away in a polish conference publication. If
anyone wants a copy I would be happy to send one on. For summary
information on the introduction, spread and a bit on the biology of
the mitten crab, the best paper to refer to is Ingle, R.W (1986). The
Chinese Mitten Crab Eriocheir sinensis - a contentious immigrant.
London Naturalist, 65, 101-105. This paper mentions records of crabs
from the Humber in the early 1980s.
Now Eriocheir appears to be extremely common in the Thames and a
recent survey of the upper estuary foreshore we undertook
encountered numerous young crabs returning up river after
post-larval settlement. The Clark et al paper also mentioned by Phil
covers some of this period.
The mitten crab is a rather exciting, though disturbing, addition to
our fauna, particularly as our rivers are not used to large
invertebrates such as these. The crabs can cause excessive damage to
flood defence systems (they form burrows in the banks - up to 30
per square metre, with sizes up to 80 cm in depth and 12cm in
diameter!). If you need to consult anybody on what to do, I guess the
best option would be to talk to the people responsible for flood
defence in European rivers, such as the Weser & Elbe. These rivers
have 'suffered' huge migrations of mitten crabs (they spawn in
estuaries, most males die but some females probably return upstream)
- in the 1930s 113,960 crabs were caught in one day.
A final aspect perhaps we need to consider about the mitten crab is
that in their native far East they are the intermediate host to the
lung fluke Paragonimus westermanii, which includes humans as a final
host and can lead to tuberculosis like symptoms and bleeding of the
lungs (I'll refrain from further detail...). The initial hosts of the
fluke are a range of aquatic snails, so the potential is there for
the fluke to complete its lifecycle in the Thames region. Currently,
though the crabs appear fluke-free in the Thames, so I thought
perhaps a way of controlling the crab would be to sell high price
fluke free crabs back to the far East! Any fishery interest out
there...?
Cheers
Martin
____________________________________________
Dr. Martin Attrill
Benthic Ecology Research Group
Department of Biological Sciences
University of Plymouth
Drake Circus
Plymouth. PL4 8AA.
Tel: 01752 232916
Fax: 01752 232970
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|