 Exotic
crab poised for widespread UK invasion
University of Newcastle upon
Tyne
An exotic type of crab is spreading at an alarming rate throughout
Britain’s coast and rivers, a new study suggests.
The Chinese mitten crab, brought to Britain during the last
century in ships’ ballast water, could cause devastating
environmental problems if populations are not monitored and
controlled, say the study’s authors.
Researchers from the University of Newcastle upon Tyne carried
out the first comprehensive modelling of the crab’s migration
through Europe and the UK. They compared the two and found
the pattern of the crabs’ ongoing invasion of the UK
is similar to the population expansion in Europe earlier in
the last century when the Continent experienced a major outbreak.
The study authors predict that the mitten crab - so called
because its claws are coated with small clumps of dark brown
fur, or mittens - has the potential to establish itself in
all major UK estuaries in several years time.
Mitten crabs are unwelcome because they prey on protected
UK native species such as the white-clawed crayfish and salmon
eggs and fry. They also settle in river banks, burrowing into
them and riddling them with bore holes up to half a metre
long which may eventually cause the bank to collapse.
The Newcastle University study, published in the academic
journal Biological Invasions, recommends that a nationwide
monitoring and trapping system for the crab should be introduced
before it is too late to control the population.
Chinese mitten crabs are already present in some of our waterways,
including the Thames, Humber and Tyne rivers and parts of
the North Sea and Channel coasts.
The study details how the UK colonisation of mitten crabs
has increased on a large scale in recent years. From 1997-1999
the spread along the coast was 448km per year - nearly six
times the average spread of 78km per year from 1976-1999.
In rivers, the increased spread from 1995-1998 was 49km per
year, around three times the average spread of 16km per year
from 1973-1998.
The UK spread was most marked along the east coast northwards
to the River Tyne and on the south coast westwards to the
River Teign.
Dr Matt Bentley, one of the research team, said: “The
pattern of the spread in the UK since the 1970s mirrors the
spread in mainland Europe and in the Baltic region which experienced
an major outbreak. This is a fairly good indication that the
UK is set for a similar situation.”
Mitten crabs can be found in the sea or rivers because they
are catadromous - meaning they mainly live in freshwater but
must migrate to the sea to breed. Their potential for widespread
colonisation is increased by the fact they can cross dry land
and can migrate up to 1,000km while growing to adult size.
A decrease in river pollution and a prolonged period of drought
in the late 1980s - which together improved habitat conditions
for mitten crabs - are potential reasons for the recent population
rise.
Dr Bentley, of Newcastle University’s School of Marine
Science and Technology added: “This study demonstrates
the importance of a monitoring programme for the mitten crab,
even if its appearance is just a rare occurrence in an estuary.
Records demonstrate the crab’s ability to rapidly expand
once the local population reaches a critical density and or
conditions become favourable.
“With most invasive species, such as the grey squirrel,
the problem is not recognised until it is too late to do anything
and you can not eliminate it without taking drastic environmental
measures.
“This study shows there is a need for a monitoring
system for the mitten crab which could help manage the spread
at an early stage. Low cost options could include a public
awareness campaign where anglers and other users of rivers
and the coastline are encouraged to report sightings of crabs.
Measures which are currently used to monitor fish in our rivers,
such as the electrical fish counters, could also be adapted
to include monitoring of mitten crabs.”
The research was funded by Newcastle University and the Esmee
Fairbairn Foundation.
Mitten crab facts:
- The crab is a delicacy in Chinese and Japanese restaurants
and is eaten raw, preferably with its reproductive organs
swollen!
- If you see a crab in freshwater it is almost certain to
be a mitten crab (only one other small non-native crab has
been reported from Cardiff Docks)
- Politician Peter Mandelson was once jokingly likened to
a mitten crab by Deputy Prime Minister John Prescott during
a photocall on the Thames.
- the mature crab is the size of a dinner plate when its
legs are extended (the body is around 8cm wide and the legs
about 12cm long)
- The scientific name is Eriocheir sinensis (from
the Greek meaning wool hand of the Chinese) and the crab
originated in the Province of Fukien, China.
- The first UK recorded sighting was at Lots Power Station,
Chelsea in 1935. However, it is likely any crabs around
then died out and were not reintroduced into this country
until the 1970s.
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