The debate surrounding the impact of farmed salmon on wild salmon populations often focuses on the issue of sea lice.
Wild salmon supporters correlate the alarming decline of wild fish to the fact that fish farms harbour unnaturally high concentrations of sea lice which destroy juvenile wild fish. Salmon farm proponents refute this theory, arguing that there is no direct scientific evidence to support this claim, and that their self-imposed regulation of sea lice levels on the farms is within reasonable and safe limits.
It is absolutely true that there is no unequivocal evidence to show a salmon farm sea louse leaving a farm, attaching to a wild salmon juvenile and then seeing that fish die as a direct result of weakness and infection caused by the louse. However, what independent scientists do see is that when wild juvenile salmon leave their spawning grounds they have no parasites, but when they approach the farms they are inundated with sea lice.
Salmon farmers use chemicals to ensure that the number of adult lice on their fish is never above three, a number which is low enough to keep their fish healthy. So what is happening?
Unfortunately, the lice are very effective parasites, and they reproduce alarmingly efficiently. With farms being stocked with up to 750,000 Atlantic Salmon, just three adult lice per fish means that each fish farm can harbour several hundred million sea lice eggs and still be within regulations. Chemicals may help the farm fish combat large numbers of parasites. The wild salmon do not have that protection.
Neither salmon farms nor the governing body of the Department of Fisheries and Oceans are under any requirements to sample juvenile fish around their fish farms to see the impact of their businesses.
The argument surrounding sea lice is like so many difficult environmental debates we are now facing. Because the ecosystems we live in are so large and so complex, it is often virtually impossible to find direct scientific correlations between cause and effect. Instead we must look at the weight of evidence to support one argument versus the other. In the example of air pollution we do not have specific evidence that the pollutants released by one individual factory or oil refinery leads to breathing problems or illness.
However it has been accepted that the cumulative worsening of air quality is harmful to human health. Therefore we protect ourselves and limit emissions.
So what about our fish? Sea lice incubated by farms are not the only cause for depletion of wild salmon stocks but they are a significant factor known to us today as illustrated by the reproduction rates above.
If we continue to look for undeniable evidence of the link between open-net fish farms and the collapse of wild salmon stocks, it is most likely that the wild fish will be long gone before we have our answers.
We do not have to make a choice between wild and farmed fish. We can keep farmed fish in closed containment, away from the oceans and migratory routes, thus eliminating infection of the wild salmon fry by the incubated lice from the open-net cage farms.
The science is in. We need to act in good faith with the weight of evidence we have available to us now.
We would like the electorate in Canada to ask each local candidate to support moving fish farms to closed containment, and away from our wild salmon.
Brian Gunn is President of the Wilderness