The biggest threat currently facing our migratory fish is the tiny ecto-parasite, Gyrodactylus salaris (Gs) – a creature which could single-handedly devastate our salmon stocks. If it ever gained a foothold here, it would destroy our unique salmon heritage. Thankfully the United Kingdom and Ireland, unlike the rest of Europe, are still officially Gs-free. But it is vital to act to ensure this status is maintained, and to prevent a national economic and environmental catastrophe.
Image by Dr Tor Atle Mo, National Veterinary Institute, Oslo
Gs is less than half a millimetre long, and attaches itself to either the scales or fins of fish. Gs both damages the fish’s skin and allows for secondary infection, and several thousand of the creatures can feed on a single salmon parr. Thankfully, the parasite cannot survive full strength sea water, so natural migration of fish is unlikely to spread infection.
Gs originated from the Baltic strains of salmon (which are resistant), reaching rivers in south-west Norway via careless movements of rainbow trout in the 70’s. Since then, 41 Norwegian rivers have been infected and their salmon populations effectively exterminated.
Gs has also spread to rivers in Denmark, Germany, France, Spain and Portugal, resulting in mass mortality of juvenile fish.
Scientific tests have revealed that Scotland’s strains of salmon are highly susceptible to Gs and if the parasite entered a Scottish freshwater system it would likely result in up to 90 per cent mortality.
Image by Dr Tor Atle Mo, National Veterinary Institute, Oslo.
Treatment of infected rivers is a long-term and highly expensive business. Rotenone – an extract from the root of the derris plant – has been used in some rivers in Norway. This kills all fish in the river, and ultimate recovery relies on restocking programmes carried out from eggs and juveniles collected prior to the poisoning. Such drastic treatment is only possible in short rivers with favourable conditions. An alternative is to use aluminium sulphate – a chemical which kills Gs but not the salmon – but both treatments are hugely expensive and offer no guarantee of success, as was recently demonstrated in Norway.
As a result, keeping Gs at the forefront of everyone’s minds will remain an on-going priority for the Association, for prevention is considerably more effective than cure.
With help from the Government, we have commissioned the production and placement of 1300 riverbank signs to ensure anglers, canoeists and other water users are aware both of the risks posed by Gs and of the appropriate action to take. The Association has also purchased supplies of disinfectant so that proprietors can provide disinfection facilities for anglers.
A detailed GS Contingency Plan has also been prepared by the Government and stakeholders in case of the worst case scenario – the announcement of an outbreak.
Image by Dr Tor Atle Mo, National Veterinary Institute, Oslo.
A series of simple procedures will ensure Gs never reaches Scotland. GS can survive for 5 to 7 days without a host in damp conditions (e.g. angling clothing, waders, wet reels, lines or landing nets).
If you have fished abroad* within seven days prior to fishing in Scotland, you must disinfect, using one of the following techniques:
- Dry equipment at a minimum of 20°C for at least 2 days
- Heat at above 60°C for a minimum of one hour
- Deep freeze equipment for at least one day
- Immerse in a solution suitable for killing Gs for a minimum of 10 minutes**
* Particularly Norway, Sweden, Russia, Finland, Denmark, France, Germany, Spain or Portugal
** Virkon, Wescodyne (1% solution), sodium hydroxide (salt water 0.2%)If you are in any doubt, disinfect. All of our member boards are on hand to provide advice to anglers.