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Global biodiversity is in decline and one of the major threats is the spreading of non-native species. Non-native species (NNS) are animals and plants that have been moved out of their natural area by human action, whether it is intentional or not. The risk of spreading non-native species is that they become invasive, displacing native animals and plants and causing damage to environments and local economies. Biosecurity measures are therefore essential to minimise the impacts of invasive non-native species (INNS) and to prevent the spread of others.

Water is an excellent transport method for the dispersal of non-native animals and plants, making rivers, lochs and their banksides particularly vulnerable to INNS. The River Tweed is home to several INNS already and is at risk from the spread of several others. As a means of controlling the spread and effects of INNS in the Tweed catchment, the Tweed Foundation, alongside the Tweed Forum and Rivers and Fisheries Trusts of Scotland, developed the Tweed Catchment Biosecurity Plan. The Plan targets three main areas:

  1. Preventing and reducing the risk of the introduction and spread of NNS into and within the Tweed catchment.
  2. Set up a plan for the detection and monitoring of NNS which is linked to plans to make sure that responses are quick.
  3. Build on the existing controls for NNS and to share knowledge with others.

Find out more about the Tweed Catchment Biosecurity Plan here.

American Signal Crayfish

Species To Look Out For

Several NNS have been highlighted in the Plan as being "high impact species", either because they already exist within the Tweed catchment, because of the risk they would pose to the local biodiversity and economy if introduced, or because of an increased risk of introduction. 

Several of these non native species can be seen below, some of which are already in the catchment while others pose a high risk if introduced.

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.

Gyrodactallus salaris

Gyrodactallus 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.

What's Being Done?

Biosecurity is hugely important in maintaining a healthy river system.  Biosecurity measures are therefore needed in order to control INNS already present in a catchment, and to prevent the introduction of others.  

The Tweed Foundation use a number of different methods to both control and prevent the spread of INNS throughout and into the Tweed catchment.   

How Can You Help?

We are always on the lookout for NNS throughout the Tweed catchment.  If you spot any non-native species or see any signs of them in or around the river, please get in touch to let us know what you have seen and where. 

Anglers and others using the water can also help prevent the spread of unwanted species by following three simple steps: Check, Clean, Dry.

A Check, Clean, Dry poster can be viewed here.

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