10-Aug-2006
- The Environment Agency has released a top-ten
most UNwanted list of foreign species that have
overstayed their environmental visa.
The American signal crayfish
and the American mink may originally be from across
the pond, but they are now taking over British
waterways, out-muscling native competition and
spreading disease. For the native white-clawed
crayfish and water vole, these invasive species
are over sized, over sexed and over here.
But these are just two of the
recent arrivals that have taken advantage of Britain’s
complimentary living conditions, with the Environment
Agency compiling the top ten invasive species
marked for containment and removal.
1. Japanese Knotweed Plant
2. American Signal Crayfish
Crustacean
3. American Mink Mammal
4. Giant Hogweed Plant
5. Floating Pennywort Plant
6. Himalayan Balsam Plant
7. Australian Swamp Stonecrop
Plant
8. Chinese Mitten Crab Crustacean
9. Parrots Feather Plant
10. Topmouth Gudgeon Fish
UNWANTED! Japanese Knotweed
(aka: Fallopia japonica)
Crime: Causing structural damage to buildings
and roads, after forming dense vegetative layers
that stop native flora germinating. Increases
risk of flooding through dead stems being washed
into rivers and stream channels, restricting access
to riverbanks and reducing land values.
Background profile: Rapidly
growing perennial plant from Asia, brought to
Britain in the mid-19th century as an ornamental
garden and fodder plant but then spread into the
wild.
Physical description: Grows
up to 2-3m tall with green bamboo-like, speckled
stems and forms dense cane-like clumps. Its leaves
are green and shield or heart-shaped, with a flat
base and are up to 120mm long. It flowers in August
– October with creamy flower clusters borne on
the tips of most stems.
Known whereabouts: Widespread
in the wild in Britain across a range of habitats
– particularly roadside verges, riverbanks and
derelict land. It is widespread across the South
Wales valleys.
If sighted: A new Japanese Knotweed
Code is being released to tackle England and Wales’
most damaging foreign species. Includes advice
on spraying herbicides containing Glyphosate during
early summer flowering stage and again in late
summer/autumn to stop regrowth. The use of an
approved herbicide in or near water requires the
prior written approval of the Environment Agency.
UNWANTED! American Signal Crayfish
(aka: Pacifastacus leniusculus)
Crime: Introducing crayfish plague (the fungi
Aphanomyces astaci) into Britain which can wipe
out entire populations of native white-clawed
crayfish. Out-competes native crayfish, expands
numbers and range rapidly, with colonisation rates
of over 1km of watercourse per year. Impacts British
invertebrate macrophyte (plants) communities.
Burrows into riverbanks creating a honeycomb of
tunnels, which can then collapse and damage the
banks.
Background profile: Imported
into the UK form North America in the 1970’s as
an attempt to create a commercial crayfish farming
industry. They are bigger, stronger and breed
faster than the native white-clawed crayfish.
Physical description: Identified
by bright red colouring under the claws and white
patches on claw joints. They are on average 16cm
long but can grow up to 30cm long.
Known whereabouts: In freshwater
lakes and rivers across England and Wales, and
is now present in parts of the Wye and Usk rivers.
If sighted: Commonly caught
in waterways of southern England using rod and
reel. If caught signal crayfish must be removed
from waterway and killed. Very tasty in a bisque.
Measures being taken: Transferring
crayfish between waterways is illegal. A ‘Crayfish
Code’ (available in a Pdf) has been formulated
by the Environment Agency to stop the spread of
signal crayfish and the crayfish plague.
UNWANTED! American Mink (aka:
Mustela vison)
Crime: Devastating predator of native wildlife
in Britain, the mink is linked to huge declines
in water vole and moorhen populations. Occasionally,
mink will indulge in "surplus killing",
taking a large number of prey at one time. They
have been known to cause damage to property, such
as boats and caravans, when scavenging for food
and may also cause problems at fish farms, hatcheries
and in game/ornamental bird enclosures.
Mink have no natural predators
in Britain.
Background profile: Native to
North America, mink were originally brought to
Britain in 1929 for use in fur farms. However
since the 1950s they have been breeding extensively
in the wild following accidental and deliberate.
They are a member of the weasel family, which
includes badgers, polecats, martens and otters.
Physical description: Brown
or black in colour and between 30-60cm long with
a slender body and short legs.
Known whereabouts: Mink are
found in aquatic habitats throughout Britain but
can spend time away from water, even including
urban areas.
Measures being taken: Mink numbers
have started to decline as our native otter population
recovers from the effects of pollution, hunting
and loss of river habitats. Otters are reported
to attack and even kill mink and it seems that
the reason mink spread so quickly initially throughout
Britain was because they had no competition.
UNWANTED! Giant Hogweed (aka:
Heracleum mantegazzianum)
Crime: Sap contains a toxic chemical that sensitises
the skin and leads to severe blistering when exposed
to sunlight. Also forms dense colonies that suppress
the growth of native plants and grasses, leaving
riverbanks bare of vegetation in winter and increasingly
erosion risks.
Background profile: Originally
from the mountainous Caucasus region of Asia that
lies between the Black and Caspian Seas, Giant
Hogweed was introduced to Britain in 1893 as an
ornamental plant.
Physical description: Looks
like a large coarse form of cow parsley, reaching
up to 4m high and produces up to 50,000 seeds.
Known whereabouts: Widespread
across England and Wales, it escaped from gardens
and is now prevalent along riverbanks, towpaths
and wasteland areas. It is present on the Usk
and parts of the Wye.
If sighted: Spray with herbicide
during the growing season (March to August), when
there is green, leafy material present. In order
to be effective, spraying must be carried out
before the plant flowers and sets seed. The use
of an approved herbicide in or near water requires
the prior written approval of the Environment
Agency.
UNWANTED! Floating Pennywort
(aka: Hydrocotyle ranunculoides)
Crime: Growing in shallow, slow-flowing eutrophic
water bodies, floating pennywort forms dense interwoven
mats of vegetation that extend up to 40cm above
the water surface and up to 50cm below. These
mats quickly cover the water surface and can grow
20cm per day, starving the waterbody of light,
nutrients and oxygen which kills many of the species
living in it and also increases the risk of flooding
by blocking the waterway.
Background profile: Originally
from North America and was brought to Britain
in the 1980s as a plant for tropical aquaria and
garden ponds. However by 1991 it had become present
in the wild.
Physical description: Has circular
or kidney-shaped, deeply lobed leaves, up to 180mm
across. The stem is horizontal with a fleshy appearance
and has leaf stalks and roots every 0.2-0.3m.
It has no flowers and can double its weight in
as little as 3 days.
Known whereabouts: Relatively restricted to about
35 sites in the south of England and south Wales.
It is very likely to spread around UK watercourses
and become a major nuisance in the future. It
is present on the Gwent Levels and effort to control
its spread has been successful but it will require
continued effort to keep this invasive plant in
check.
If sighted: Use a herbicide
containing Glyphosphate or 2,4-D amine, and cut
and remove 2-3 weeks later. Very difficult to
control due to its rapid growth rates. The use
of an approved herbicide in or near water requires
the prior written approval of the Environment
Agency.
UNWANTED! Himalayan balsam (aka:
Impatiens glandulifera)
Crime: Grows in dense stands that shade out native
grasses and other flora. In the autumn, the plants
die back, leaving riverbanks bare of vegetation
and vulnerable to erosion. Produces more nectar
than any native European species of plant, which
makes it a more attractive option to pollinating
insects such as bumblebees, luring them away from
native flowers which suffer from less pollination.
Background profile: Originating
in the Western Himalayas and introduced to Britain
in 1839, Himalayan balsam escaped from gardens
and rapidly colonised riverbanks and areas of
damp ground.
Physical description: It is
an annual plant that grows up to 3 m tall with
pale to purplish-pink slipper shaped flowers in
June - October.
Known whereabouts: Himalayan
balsam grows on riverbanks and shoals in the river
channel. It is very extensive in the South Wales
valleys.
If sighted: Spray with a herbicide
containing Glyphosate or 2,4-D amine in early
spring for best effect. Control measures should
aim to prevent flowering and if this is achieved
before seeds are set, eradication is possible
in two to three years. The use of an approved
herbicide in or near water requires the prior
written approval of the Environment Agency.
UNWANTED! Australian swamp stonecrop
(aka: Crassula helmsii)
Crime: Destroys pond-life, pushing out native
vegetation, by rapidly forming a mat over the
water surface, which continues to grow upwards
like a huge sponge. It will even spread into the
turf and destroy the pond itself. Anything living
beneath this mat is killed through lack of light,
oxygen and eventually water itself. As well as
being considered unsightly and detrimental to
landscape quality it can also severely inhibit
navigation, fishing and many other forms of water-related
sport and recreation on affected watercourses.
Also destroys shingle habitat, which is used by
some nesting birds.
Background profile: Introduced
to Britain from Tasmania in 1911 and sold as an
‘oxygenating plant’ in garden centres. Since 1956
has been aggressively spreading in the wild.
Physical Description: There
are 3 different typical growth types – a terrestrial
form, an emergent form and a submerged form. These
forms however remain interchangeable depending
on the environmental conditions. It is greenish
yellow, with fleshy leaves and has small white
flowers from June – September. Grows vigorously
all year round and colonises any still or slow-moving
water body ranging from damp ground to water 3m
deep.
Known whereabouts: Found growing
on damp soil, in shallow water or submerged in
ponds, lakes and wetlands and has spread throughout
England and Wales. It is known to be present in
Llyn Tegid.
If sighted: The plant is best
treated at the early stages of infestation. Delay
will cause problem several orders of magnitude
worse in each successive year until Crassula actually
destroys the pond itself. On submerged material
use herbicide containing Dichlobenil in March.
On emergent material use Glyphosate at 6litres/ha
at least twice a year between March and October.
The use of an approved herbicide in or near water
requires the prior written approval of the Environment
Agency.
UNWANTED! Chinese Mitten Crab
(aka: Eriocheir sinensis)
Crime: Known to burrow into riverbanks, presenting
a hazard to river and other freshwater engineering
projects. Out-competes many native species. The
crab is capable of emerging from water and crossing
dry land to enter new river systems. Could eventually
threaten freshwater habitats currently occupied
by populations of our native crayfish (Austropotamobius
pallipes). Is the secondary host of a parasitic
lung fluke (Paragonimus ringer) that can infect
mammals including humans, if eaten raw or poorly
cooked.
Background profile: Originated
in southeast Asia and thought to have been introduced
to Britain in 1935 through ballast water on ships.
The crab is a delicacy in Asia and is eaten raw.
Physical Description: A large
crab with a shell width of approximately 80 mm
and legs that are one and a half times its width.
It has "mittens" on its claws that are
actually lots of soft bristles or setae.
Known whereabouts: Found in
estuaries, lakes, riparian zones, water courses
and wetlands. Mitten crabs spend the first five
years of their lives upstream in fresh water and
then migrate seawards and gather in large numbers
to breed in estuaries. Largest populations in
Britain are found in the Humber, Thames and Medway
estuaries. The population in the Thames probably
runs into millions and they occur throughout the
estuary and lower freshwater reaches of the river.
If sighted: Environment Agency
fisheries staff conduct regular trapping of Chinese
Mitten Crab in affected waterways in an attempt
to stop the spread of this crustacean.
UNWANTED! Parrots feather (aka:
Myriophyllum aquaticum)
Crime: Forms dense mats of vegetation in waterways
starving other species of sunlight, nutrients
and oxygen, eventually killing them. Also severely
inhibits navigation, fishing and many other forms
of water-related sport and recreation on affected
watercourses. Now adapting the British winters
by becoming more frost resistant. Dense appeared
on surface of water can lead children to think
solid ground is underneath, increasing risk of
drowning.
Background profile: Originated
from lowland central South America and was first
found in Britain in 1960 and has now spread to
about 150 sites. Widely grown in garden ponds
and though not usually deliberately introduced
into the wild, seeds can be concealed in soil
of other nursery-sourced plants.
Physical Description: Bright
green in colour, has fleshy and brittle stem with
feathery emergent shoots, but no flowers. Only
female plants are present in Britain, so spreads
by vegetative means only.
Known whereabouts: Grows in
ponds, reservoirs, gravel pits, streams canals
and ditches.
If sighted: Use a herbicide
containing Dichlobenil in spring to shallow water
and areas of damp ground. Material should be cut
and removed as often as necessary and at least
every 6 – 9 weeks from March to October to weaken
the plant. The use of an approved herbicide in
or near water requires the prior written approval
of the Environment Agency.
UNWANTED! Topmouth Gudgeon (aka:
Pseudorasbora parva)
Crime: Out-compete native species such as roach
and rudd because it matures at one year old, whereas
a rudd does not mature sexually until two or three.
It can also breed up to four times a year. May
carry a damaging parasite, which is believed to
interfere with the breeding cycle of salmon and
trout.
Background profile: Small Asiatic
member of the carp family, appeared in mainland
Europe in the 1960’s. Has been introduced accidentally
into a number of British lakes.
Physical Description: Measuring
only 3-4cms in length, the males are usually darker
in appearance than females. Often confused with
juvenile native species, although their appearance
is quite distinct.
Known whereabouts: Found in
waterways across England and Wales.
Measures being taken: Environment
Agency fisheries staff conduct regular electro-fishing
of affected waterways in an attempt to stop the
spread and eradicate this fish.
All above plants are covered
by pest-control legislation: The Wildlife and
Countryside Act 1981 provides the primary controls
on the release of non-native species into the
wild in Great Britain. It is an offence under
section 14(2) of the Act to ‘plant or otherwise
cause to grow in the wild’ any plant listed in
Schedule 9, Part II.
For guides on how to approach
these invasive species, go to http://www.environment-agency.gov.uk
and search for ‘invasive species’.
For images of any of these species
– and professional pictures of recent Topmouth
Gudgeon eradication taking place – please contact
the press office.
Heledd Evans
