Viruses and Atlantic Salmon

“Aquaculture escapees carried the most viruses of any group we studied and frequently had multiple infectious agents present. Our study looked at returning adult wild salmon, the survivors, so we weren’t able to see how out migrating smolt were affected as they passed near sea-cages in a critically vulnerable period of their life. This type of research will help us better understand the disease risks where wild and industrial fish overlap.” – Jonathan Carr, V.P. Research and Environment, Atlantic Salmon Federation

This week we have seen an extremely important report from the Atlantic Salmon Federation confirming what campaigners have known for years, but have to date been unable to prove, the link between the presence of viral diseases in farmed salmon and the decline in the wild populations of salmon and salmonids such as sea trout. The summary reads in part:

“The results confirmed that intercontinental transmission of infectious agents is likely occurring in offshore waters near Greenland between Atlantic salmon of North American and European origin. Analysis also showed that among the groups analyzed, aquaculture escapees had the highest prevalence of viruses and multiple infections were common among both cultured and wild fish.”

There is no reason whatsoever to suppose that what has been happening on the West side of the Atlantic Ocean hasn’t also been happening on our West coast. It is also the case that the major cause of the mass mortality events that happened in mid-Argyll last Autumn were largely attributable to another, but similar, viral disease, salmon cardiomyopathy. We have written about this before; briefly it’s a new arrival in Scotland that came from Norway a few years ago, is incurable and gives no external signs of its presence until the salmon are on the point of death. When it was detected MOWI took the decision to cull all remaining stocks in most of its “farms” in mid-Argyll, before the disease took them, at which point they would have moved from being a marketable product to Category Two waste that cannot by law enter the food chain. The event has made it into the current Private Eye, see above image.

It’s beginning to look as if the problems for this beleaguered industry aren’t confined to sea lice. With this year having already seen unseasonably warm days there’s no reason for any wishful thinking that viruses won’t return. We hope that Marine Scotland and the Fish Health Inspectorate will read the study and appreciate that viruses, like salmon, don’t know about borders.

The study can be found here: Atlantic Salmon Federation