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Synopsis of the Tweed Foundation's seminar on Gyrodactylus Salaris held on Tuesday, 2nd November 2004 at the Cross Keys Hotel in Kelso.
Contributors:
Professor Randolph Richards (Chair)
Director, The Institute of Aquaculture, Stirling University & RMB Professor of Clinical Fish Pathology
Professor Christina Sommerville (Speaker)
Professor of Aquatic Pathology, The Institute of Aquaculture
Doctor Andy Shinn (Speaker)
The Institute of Aquaculture
Doctor Carey Cunningham (Speaker)
Fisheries Research Services, Aberdeen
Mr Vidar Skiri (Speaker)
River Manager, River Rauma, Norway
Attendees:
Approximately 100 people including representatives from SEERAD,EA, SNH, AST, FRS, RTC, TF, NASCO, Tweed Forum, Local Angling Associations and Tweed proprietors, other River Boards (Nith, Eden, Ayrshire rivers),Tweed boatmen,bailiffs and interested anglers.
WHAT IS Gyrodactylus salaris (Gs)?
Invisible (parasite) to the naked eye,0.5 millimetre in length, only one needed to breed, when one Gs is born it is already producing the next two generations (one becomes 6 million within 4 weeks).
Attaches itself to fish skin by tiny claws. A young salmon can host 10,000 before it dies.
Very difficult to identify from other Gyrodactylus species, none of which are fatal to salmon (computer programs now available to assist identification-principally by the shape of the claws).
Gs can travel on its own and can survive for six days off a fish.
Gs cannot tolerate full concentrate sea water but survives happily in brackish water. It will attach to other salmonid and non-salmonid species but at certain levels of infestation these other fish develop immunity, as do Baltic salmon. However, Gs is thought to be lethal to almost all genetic strains of Atlantic salmon as evidenced by affected rivers in Norway and Russia (and as tested on Scottish fish).
Experience from Norwegian rivers is that Gs leads rapidly to the almost total extinction of Atlantic salmon.
WHICH COUNTRIES ARE AFFECTED AND HOW CAN IT BE TRANSMITTED?
Due to identification difficulties there is some doubt regarding the Gs diagnosis in the non-Scandinavian countries (except Russia), but current known distribution shows that the UK, Ireland and Iceland are the only countries unaffected which face onto the Atlantic and North Sea. The UK is therefore surrounded on its south and east sides, down as far as Spain and Portugal in the south and extending to all Baltic countries (where Gs originated) in the east.
Most transfers of Gs have been on live fish (in Norway and Russia stocking with Baltic salmon parr), but some Norwegian rivers have been infected by Gs travelling from other infected rivers in the same estuary/fjord, thereby proving its ability to survive in less than full-strength saline sea water and travel through brackish water from one river to another.
It can also be transported on fishing gear, canoes, dogs, etc. but the chances reduce to negligible amounts the longer Gs is out of water and dry (it can survive for long periods in damp, not even fully wet, conditions, e.g in plastic bags or on dead fish).
LIVING WITH Gs AND THE LESSONS OF THE RAUMA AND OTHER AFFECTED NORWEGIAN RIVERS
45 rivers have been infected; 15 are now Gs free after Rotenone treatment;11 have been treated with Rotenone and the remainder are awaiting treatment.
Rotenone kills all fish in the river by removing the oxygen, but all other aspects of the river environment return quickly to pre-treatment status after Rotenone has been applied.
Some rivers have needed more than one treatment and the Rauma is still not free of Gs after 22 years.
Particular emphasis was placed on speed of reaction to an outbreak because delay allows the parasite to proliferate unchecked and within three years there are no young salmon left in the river.
Other methods, such as barriers to stop returning fish entering infected parts of the river, can be used together with ingathering of broodstock in hatcheries to preserve the genetic stock while the process of eradication is on-going.
Aluminium sulphate treatment which kills the parasite but not the fish is being trialled in Norway.
A Rotenone treatment is expensive and requires substantial manpower and money even on the Rauma which is 46 km long (in contrast with the Tweed which has 3,000 km of river including all the tributaries in which juvenile salmon are present).
The clear message is that infection is a disaster and, although a contingency plan is essential so that action can be taken quickly, all possible care must be taken to stop any outbreak in the first place.
CONCLUSIONS AND ACTIONS
Take all possible steps to avoid infection which will almost certainly be disastrous for Tweed. It has taken 22 years to try to eliminate Gs from the Rauma using Rotenone and it has still not been successful (they are planning another application in 2006). The Rauma is only 46 km long: would Rotenone or aluminium sulphate ever work on Tweed with 3,000 km of river in which salmon live?
Steps to avoid infection include:-
Rigid control and monitoring of all live fish being brought into the river catchment (including ponds) to include the banning of live bait fishing; Rigorous disinfection procedures mandatorily applied to all anglers and their kit if they have been fishing in infected countries (or possibly anywhere outside the UK) in the previous 4 weeks (to be applied to all river users, e.g. canoeists); The RTC and other River Boards to be responsible for ensuring strict compliance with these necessary controls on infection from importation of live fish (historically the most likely route) and from anglers and their kit coming from abroad.
Carry out effective lobbying of both the UK and Scottish Governments to fast track the preparation of a credible and effective contingency plan in the event of any UK river becoming infected. This is essential to avoid paralysis and delay in the event of Gs arriving.
The biggest lesson from Norway is that delay and prevarication are disastrous and can result in the complete loss of viable salmon fisheries for a generation or more.
Internationally, to lobby both the UK and Scottish Governments not to allow any relaxation of live fish import restrictions from Gs affected countries and to have it acknowledged in the EU that the imperative for free trade is secondary to the need to protect UK and Irish salmon fisheries from Gs infection.
The above to be coupled with constant monitoring of all EU countries for incidence of Gs and that the latest techniques for identifying Gs are used throughout the EU to ensure that those countries that are designated now are truly affected and that there has been no misidentification ( which more than one speaker thought was the case with France, Spain, etc). Difficulties of identification are a real concern because it is equally possible that Gs has been identified as a harmless Gyrodactylus, so tiny are the physical distinctions between Gs and its harmless strains.
To encourage Norway, and all other countries bordering the North Sea and the Atlantic, to get rid of Gs in all its rivers as soon as possible, to recreate the buffer between the UK, Ireland and Iceland and the Baltic states so that the chances of infection from the Baltic (where Gs has been for centuries) return to their pre-1975 level and to encourage those countries infected since 1975 to establish rigid controls to ensure that Gs cannot escape again from its natural Baltic environment.
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