Isle of Man

Invasive species data & legislation

There are 18 invasive species listed on the Global Invasive Species Database (GISD), of which 12 are categorised as alien-invasive species. These are the perennial freshwater herb parrot’s feather milfoil Myriophyllum aquaticum , three shrubs; Buddleja davidi, Japanese Knotweed Fallopia japonica, and Rhododendron ponticum. One herb; Himalayan balsam Impatiens glandulifera and two alien invasive fish; northern pike Esox Lucius and the gregarious, freshwater fish Phoxinus phoxinus. Six alien invasive mammals; the European hedgehog Erinaceus europaeus, House mouse Mus musculus, ferret Mustela furo, the Norway rat Rattus norvegicus and the European red fox Vulpes vulpes. There are no known introduced amphibians or reptiles.

The only avian invasive species listed on GISD is the native domestic pigeon Columba livia, however, the Rose-ringed Parakeet Psittacula krameri is a vagrant, and the Ruddy Duck Oxyura jamaicensis has visited the island from an introduced population in Great Britain.

Other native invasive species listed are the common red algae Polysiphonia brodiei, the stoat Mustela ermine and three species of fish; Roack Rutilus rutilus, Atlantic salmon Salmo salar and Brown trout Salmo trutta. Two marine invasives mentioned in the government’s 2014 newsletter are Sargassum seaweed, also known as wireweed, and the carpet sea squirt Didemnum vexillum.

Schedule 8 of the Wildlife Act lists non-native species that are established in the wild and continue to pose a conservation threat to native biodiversity and habitats, such that further releases should be regulated. Eleven non-native terrestrial animals and 31 plants species are recorded to be established in the wild on the Isle of Man, for the complete list see National wildlife legislation includes the Destructive Imported Animals Act 1963 and Wild Animals (Restriction on Importation) Act 1980. Incentives for control of invasive weeds were included in the pilot Agri-environment Scheme. Invasive weed control is a condition of the Countryside.

Problems with invasive non-native species

Japanese knotweed is the most invasive plant in Britain and is very difficult to control. It spreads rapidly, especially on waste ground and next to streams and rivers. It shades out native plants, posing a threat to biodiversity, its roots and stems also cause structural damage to buildings. Himalayan balsam also competes with and displaces native plant species. Rhododendron can form dense stands which can inhibit the regeneration of native species and alter plant and animal communities. Sargassum (wireweed) is widely colonised in the south of the Island, manual weed removal has proved ineffective.

The ‘New Zealand’ flatworm, Arthurdendyus triangularus and ‘Australian’ flatworm, Australoplana sanguinea, are non-indigenous flatworms predominantly found in gardens where they pose a potential threat to native earthworm populations. They could also, given time, have an impact on wildlife species dependant on earthworms and have a deleterious effect locally on soil structure.

Hedgehogs threaten native invertebrates, reptiles, amphibians and ground-nesting bird nests (such as the little tern) through predation; they also compete with native insectivores. Brown rats have been monitored recording the eggs of Arctic terns. The ferret is a threat to native prey species, particularly ground nesting birds.

Priority invasive non-native species and actions

There is ongoing herbicide control of Japanese knotweed along water courses. The Government pages for Japanese knotweed are at;  

Information and advice on the control of injurious weeds can be found at;  

Parrot’s feather milfoil Myriophyllum aquaticum has been successfully controlled by the Société Guernesiaise at one of their nature reserves and control efforts are ongoing elsewhere on the island.

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