Rita
Penman - 5-Aug-2008 - Over recent days hundreds
of dead crayfish have been seen in the lower
River Colne in Colchester. Crayfish plague
or another disease is suspected as the cause.
Following reports from
a Castle Park Ranger, Environment Agency
staff confirmed the deaths and sent samples
for analysis.
The CEFAS (Centre for
Environment, Fisheries & Aquaculture
Science) lab in Weymouth is analysing the
animals to see if they are infected with
the highly virulent fungal disease Aphanomyces
astaci, commonly known as crayfish plague.
This outbreak follows
hot on the heels of a similar outbreak on
the River Waveney in October last year.
Having two such outbreaks so close in time
and place is very unusual. It shows more
needs to be done to prevent the spread of
this disease.
The animals affected
in both cases are Turkish crayfish – an
alien invasive species, which has died in
its hundreds over the past few weeks.
However, if the disease
spreads to other river systems, the rare
native white-clawed crayfish could also
be affected and crayfish plague has already
wiped out many populations of this species.
The Environment Agency
is alerting all anglers and other river
users to the potential presence of this
disease and asking that, as a precaution,
they thoroughly clean their equipment before
using it in any other waters to stop this
disease from spreading once again.
Crayfish in the Colne
belong to a non-native or alien species
called Turkish or narrow-clawed crayfish
which originates from eastern Europe and
western Asia, originally imported to supply
the restaurant trade. In common with other
European species, this is susceptible to
crayfish plague.
The population in the
Colchester area has been known for a number
of years. The presence of this large species
can cause problems such as burrowing into
banks, taking anglers bait and preying on
river invertebrates and fish eggs. So a
thinning or loss of this species from the
Colne is not a problem in itself. However,
there is great concern that the plague could
spread to other river systems.
This virulent disease
has wiped out many populations of our native
white-clawed crayfish in England and Wales.
Alien crayfish species from America, notably
signal crayfish, carry the disease but are
not susceptible to it. It is spread by affected
crayfish or, more commonly, equipment such
as fishing nets, boats etc being transferred
from infected waters.
White-clawed crayfish
were formerly widespread but have been wiped
out from many rivers and now exist in increasingly
isolated populations. There is so much concern
for the future that it has been designated
a Biodiversity Action Plan species as part
of the UK’s response to the 1992 Rio Earth
Summit and protected by EU legislation (Habitats
Directive). The only remaining populations
in Suffolk and Essex are in the Stour, Blackwater
and Chelmer.
The Environment Agency
is strongly advising that anyone using equipment
in the river take recommended precautions
before using the same equipment in any other
river system.
Anything that comes
into contact with the water – keep nets,
footwear, boats, farm machinery etc – could
potentially spread the disease. To stop
this happening, carry out the following
steps:
Clean off any mud or
vegetation and remove any standing water
Then either
Thoroughly dry the equipment,
preferably in sunlight making sure all nooks
and crannies are dry.
Or
reat with a proprietary
disinfectant capable of killing fungal spores.
(Please contact the Environment Agency for
further information about this option).
There is no need to
carry out these precautions if equipment
is being moved to another site within the
Colne.
It is not known how
the disease spread to the Colne or the Waveney,
but it is likely that it was through contaminated
equipment, possibly even an unlicensed crayfish
trap. This underlines the need to carry
out these precautions. If the same situation
had occurred in the Chelmer, it would have
lead to the eventual loss of this species
from Essex.
Julia Stansfield, fisheries,
recreation and biodiversity officer for
the Environment Agency said: ‘This second
outbreak is really worrying for the future
of our native crayfish. Without a change
in people’s behaviour, it seems only a matter
of time before one or more populations of
native crayfish is wiped out. We urge all
river users to clean and dry or disinfect
any equipment before taking it from one
river or lake to another. A few careless
acts could lead to the loss of this fascinating
species from East Anglia.
‘One possible route
for the spread of this disease is use of
unlicenced crayfish traps. The idea of this
‘wild food’ is much in vogue. While this
is safe to do in parts of the country where
native crayfish have already been wiped
out, in the east of England we are trying
to protect one of the last strongholds.
‘If members of the public
notice dead crayfish in any other rivers,
please let the Environment Agency know as
soon as possible.’
The number to contact is 0800 80 70 60.
ENDS
Notes for editors
Native crayfish
Ecology
The white-clawed crayfish
lives in a variety of freshwater habitats
including streams, rivers, lakes and reservoirs
and is the only native species of crayfish.
It feeds on a variety of vegetable and animal
matter and is itself food for certain fish
and other animals e.g. mink and otters.
They mate in autumn and the female carries
the eggs and young until early summer. The
young take 3-4 years to mature.
National status
It is found in clean,
calcareous streams, rivers and lakes in
England and Wales and occurs in a few areas
in Northern Ireland, but many populations
have been lost since the 1970s. It is particularly
scarce in southern England where populations
are becoming increasingly isolated. There
is a declining number of catchments in England
and Wales which are completely free from
non-native crayfish.
In Europe this crayfish
was formerly widespread in France, Spain
and Italy, but populations are now confined
to a diminishing number of areas.
Threat
1. Non-native crayfish species and crayfish
plague
By far the biggest threat
to native crayfish comes from introduced
species and the disease they carry called
crayfish plague. Signal crayfish, originally
from America, is the most common alien species.
It carries but is not susceptible to crayfish
plague, which can wipe out whole populations
of native white-claws. Signal crayfish is
also a very fertile, aggressive and invasive
species and will out-compete other species.
Other non-native species include Turkish,
noble and red swamp crayfish. They can all
out-compete native crayfish and noble and
red swamp crayfish also carry plague.
2. Poor habitat
White-clawed crayfish
benefit from structure within the water
body where they live. This enables them
to shelter from predators (including larger
members of their own species) and high river
flows. Suitable cover can be provided under
cobbles, boulders and other large solid
objects as well as tree roots and other
plants. Where management has removed such
structure, populations can be limited to
below sustainable levels.
3. Poor water quality
Pollution, particularly
pesticides and sewage, can also create unsuitable
conditions through direct toxicity or reduction
of oxygen concentrations
The Environment
Agency is the leading organisation for protecting
and improving the environment in England
and Wales. We are responsible for making
sure that air, land and water are looked
after by today’s society, so that tomorrow’s
generations inherit a cleaner, healthier
world.
