Salmon and Trout Association: Alien Species

Alien species are non-native species of plants or animals, which adversely affect the habitats they invade economically, environmentally and/or ecologically. Alien species can cause significant problems to our native animals and plants and annually cost millions of pounds to manage. In 2007, the Minister for Biodiversity stated that non-native invasive species cost Britain £2 billion every single year.

Hundreds of freshwater species have been moved outside their native ranges, by deliberate introductions, ballast waters of international shipping, canals, and releases from aquaria, gardens and bait buckets. This has resulted in many waterbodies now containing more than ten alien species each.

Introduced fish and invertebrate species are a great threat to our native populations. They predate, outcompete and displace native species from their preferred habitats. They can also spread parasites and introduce novel diseases, to which native populations have no natural immunity. Invasive species threaten native biodiversity by dominating native species.

Some invasive alien species can also have indirect impacts on our native fisheries by influencing the ecosystems they invade. For example, invading primary consumers, such as molluscs, disrupt food-webs from the base, and aquatic plants affect the water quality and quantity of primary production, leading to changes in dissolved oxygen levels and thus impacting fish distributions.

Alien species can cause far-reaching ecological imbalances within watercourses, and controlling their spread is vital if we are to protect native species and their habitats.

It is widely believed that a stressed system is more susceptible to alien species invasions, because the disturbance caused by other environmental stressors provides them with an opportunity to invade. The ecological implications of alien species in already stressed systems are not well understood, and could make future management difficult. Currently, under the Water Framework Directive, alien species cannot, on their own, be a reason for a waterbody to fail ‘good ecological status’. S&TA views this as ridiculous, as the presence of dominant alien species may indicate a stressed ecosystem.

The top ten ‘high impact’ alien species, according to the Water Framework Directive (see: WFD) Risk Assessment, affecting water bodies have been identified as;

Australian swamp stonecrop (Crassula helmsii)
Floating pennywort (Hydrocotyle ranunculoides)
Water Fern (Azolla filiculoides)
Parrot’s feather (Myriophyllum aquaticum)
Common cord-grass (Spartina anglica)
Japanese weed (Sarassum muticum)
North American signal crayfish (Pacifastacus leniusculus)
Zebra mussel (Dreissena polymorpha)
Chinese mitten crab (Eriocheir sinensis)
Slipper limpet (Crepidula fornicata)

However, the same report listed over 50 other alien species, although their probability of becoming invasive was unknown, and further data is urgently required. The list includes freshwater molluscs, copepods and oligochaetes (for full report see EA. (2008). WFD Technical Assessment of Alien Species in further information)

Management

The Wildlife and Countryside Act 1981, under Schedule 9, and the Prohibition of Keeping or Release of Live Fish Order, makes it an offence to introduce non-native species of fish into the wild without a licence issued by Defra or the Welsh Assembly Government. Currently, however, there is no control on the release of invasive alien species into the wild, apart from those listed on Schedule 9.

Recently Defra consulted on proposals to update the list of non-native animals and plants under schedule 9 of the Wildlife and Countryside Act 1981, for the S&TA response to the consultation click here.

The Salmon and Freshwater Fisheries Act 1975, under section 30, also requires written consent from the Environment Agency, for introductions of all native or non-native fish into inland waters, other than fish farms.

Action

S&TA feels that the focus should be on Prevention, rather than cure. Education of the implications and damage to native ecosystems caused by alien species must be translated to the general public to help prevent accidental introductions.

Further research is also required to understand the implications that alien species are having on our native ecosystems, and risk assessments are urgently required for alien species whose impacts are currently not understood.

For further information see;

S&TA/Buglife Briefing Paper: The Impact of Non-Native Species - Case Study: The Signal Crayfish
EA. (2008). Rivers Map of Alien Species Pressures
EA. (2008). Transitional Waters Map of Alien Species Pressures
EA. (2008). Lakes Map of Alien Species Pressures
EA. (2008). WFD Technical Assessment of Alien Species
Defra. (2007). Importing non-native animals
Defra. (2001). Review of Policy on non-native species