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Non Native Species

Non Native Species

There are 36 non native species outlined in the Tweed Biosecurity Plan as being a risk to the Tweed, either because they are already present, because of their increased risk of being introduced or because of the risk they would pose to the ecosystem and the local economy if introduced.  18 plus of those species have been highlighted as being the main species to focus on and some of these can be seen below.

Signal Crayfish

Signal Crayfish are a North American species non-native to the Tweed but in recent years they have been found in several locations throughout the Tweed catchment.


The Bullhead is a species native to the South of England but not to the Tweed.  It has recently been found in a tributary to the Tweed.

Pink Salmon

Pink Salmon (native to the Pacific Ocean) were introduced to the Atlantic Ocean and are now occasionally found in rivers across Scotland, including the Tweed.

Giant Hogweed

Giant Hogweed, native to the Caucasus Mountains and Central Asia, is an invasive species of plant found on the banks of the River Tweed.

Japanese Knotweed

Japanese Knotweed, native to East Asia, is one of the more common invasive non-native species throughout Europe and North America.

Himalayan Balsam

Himalayan Balsam is native to the Himalayas but has successfully spread throughout much of the Northern Hemisphere.

Gyrodactylus salaris

Gyrodactylus salaris is a freshwater external parasite of Salmon.  It is not yet found in the Tweed but if it does reach Scotland it could have a catastrophic impact on Salmon.

Killer Shrimp

Killer Shrimp are a voracious predator and can do serious harm to freshwater ecosystems.  Killer Shrimp have not been found in the Tweed system but they have now been found in England.

Chinese Mitten Crab

The Chinese Mitten Crab reached Europe in the 20th Century and is now found in rivers throughout England, including the River Tyne.  This species poses a high risk if introduced to the Tweed.

Other Invasives


American Mink
Introduced fish from stillwaters


Skunk Cabbage
Monkey Flower
Australia Swamp Stonecrop
Curly Waterweed
Canadian Pondweed
Nuttal's Pondweed

Diseases and Parasites


Invasive Threats

Zebra Mussel
Parrot's Feather

Information on all of the above species can be found in section 4.3 of the Tweed Catchment Biosecurity Plan.

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