Ian Roberts, a salmon farmer in B.C., in his letter of June 4, correctly criticizes me for claiming sea lice have been blamed as a major reason for the collapse of sockeye runs in the Fraser River. It is difficult to define a precise cause for the declines of some runs.
However, a number of recent scientific articles have shown correlations of proximity of salmon farms with wild salmon declines (e.g Connors, B.M. et al. 2012, Migration links ocean-scale competition and local ocean conditions with exposure to farmed salmon to shape wild salmon dynamics, Conservation Letters), and in the Cohen report to Michael Kent (Technical Report 1) it is suggested that Caligus sea lice should be considered as a candidate for parasite-associated mortality of sockeye salmon smolts, the stage migrating to sea.
Roberts, therefore, throws doubts on my criticism of Trevor Taylor’s column in my letter of May 25. Trevor Taylor’s main points were: (1) salmon escaping from aquaculture sites were not a matter of concern; (2) sea lice occur naturally, so are not a problem in farmed salmon; (3) infectious salmon anemia is a naturally occurring disease, and may equally affect wild salmon, which have a natural mortality rate of around 20 per cent.
Taylor was incorrect on all these points, which anyone can read up on Google. Too bad natural marine mortality isn’t 20 per cent, although we’d probably be up to our necks in salmon if it were. However, a nasty fact remains, that wherever salmon farms are located in proximity to wild salmon rivers, the local wild stock declines.