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Potential Bio-Security Issues

The invasive non native species below are not currently present within the Esk district. They have been split into two categories depending on the degree of threat each of the new species pose to the local economy and bio-diversity in combination with the likelihood of their introduction.

Class A = Species with Severe consequences for local bio-diversity and economy and a High to Medium risk of introduction

Class B = Species with Moderate consequences for local bio-diversity and economy with a Low to High risk of introduction

There are five Class A (high risk) species for introduction into the Esk systems and they include the fish parasite Gyrodactylus salaris, three freshwater invertebrates and two aquatic plant species (Table 1).


Table 1 - Class A Species, their Impacts and Risk of Introduction

Gyrodactylus salaris (Freshwater external parasite of salmon) High- Through unintentional introduction from anglers and water sport enthusiasts through:
  • contaminated fish
  • clothing/equipment which has been in contact with infected water including canoes
  • Ballast water
  • Catastrophic impact on salmon (Salmo salar) populations throughout Scotland.
  • Has largely exterminated S. salar in 41 Norwegian rivers
Australian swamp stonecrop (Crassula helmsii) High - Through introduction from two existing populations nearby other pathways include:
  • Garden trade
  • Disposal of garden waste
  • Secondary spread by animals and human activity
  • Suited to a wide range of slow moving freshwater systems.
  • Out competes native species.
  • Forms dense carpets choking ponds and ditches.
  • Reduced light levels below the rafts can cause die off of waterweeds and algae and reduce water oxygenation levels
Zebra mussel (Dreissena polymorpha) Freshwater Bivalve Medium-through unintentional introduction from contaminated boat hulls and engines and bilge water.
  • Major economic impact on all subsurface water structures e.g. blocking pipes and impacting hydro-electric schemes
  • Varied and unpredictable ecological impacts including changes to freshwater nutrient cycles, extinction of local mussels, changes to stream substrate affecting spawning areas
Chinese mitten crab (Eriocher sinensis) Resides in freshwater but migrates to the sea for breeding. Medium-through unintentional introduction from boat hulls and live food trade.
  • Burrowing in high density populations damages river banks
  • Concern over impacts on local species
  • Intermediate host for the mammalian lung fluke Paragonimus ringer, known to infect humans

Curly waterweed (Lagarosiphon major)

Medium - found in a small number of locations throughout Scotland especially in the central belt area and spread through:
  • Garden and aquatic trade
  • Fragmentation exacerbated by wind dispersal, boat movement, angling equipment and possibly water fowl
  • Capable of forming very dense infestations in suitable habitats and occupying the full water column in waters up to 6m deep with significant impacts on native plants, insects and fish.
  • Classified as a serious threat to tourism, angling, boating and other recreational pursuits as well as conservation goals


There are also a total of 15 Class B species of which there is a high risk of introduction for two species, a medium risk of eight species and a low risk for the remaining five species (see Table 2).


Table 2

Ruddy duck (Oxyura jamaicensis)


Could migrate from a number of locations in Eastern Scotland

Orfe (Leuciscus idus)


Through intentional/unintentional introduction from an existing population nearby.

Water primrose (Ludwigia grandiflora)


Unintentional introduction from boat hulls and the pond and garden trade

Water fern (Azolla filiculoides)


Through intentional/unintentional introduction from numerous locations throughout Scotland, especially central belt

Slipper limpet (Crepidula fornicate)


Unintentional introduction from boat hulls???

Didemnum Tunicates / sea squirts (Didemnum vexillum)


Unintentional introduction from marine fishing boat hulls

Wireweed (Sargassum muticum)


Unintentional introduction from marine fishing boat hulls??

Ruffe (Gymnocephalus cernuus)


Currently recorded in central Scotland and could be introduced as live bait or in ballast water

Bullhead (Cotus gobio)


Translocated species recorded in central Scotland that could be introduced deliberately or as live bait

Common cord grass (Spartina anglica)


One location near St Andrews

Large flowered waterweed (Egeria densa)


Only found to date in East Lothian possible introduction from garden and/or pond trade

Floating pennywort (Hydrocotyle ranunculoides)


Currently only in England up to the midlands possible introduction from garden and/or pond trade

Parrot's feather (Myriophyllum aquaticum)


Through intentional/unintentional introduction from two existing populations in the south of Scotland

Fanwort (Cabomba caroliniana)


Only found in one location in southern Scotland possible introduction from garden and/or pond trade

Asian topmouth gudgeon (Pseudorasbora parva)


Currently only recorded from 5 locations in England. Could be introduced as live bait, in ballast water or through aquaria trade