Department of unintended consequences: with wild fish populations plummeting worldwide, aquaculture seemed like the best way to satisfy the world’s ever-growing appetite for fish. Oops: according to a new study in the journal PLoS Biology, that come into contact with
Salmon aquaculture now produces more than one million tons of fish per year. But that doesn’t mean wild salmon stocks are left alone to rebuild. Farm-raised salmon that escape from the open-net pens along coasts—which is how most salmon farms are set up—breed with wild populations, earlier studies showed, meaning the progeny are no longer truly wild. Also, the crowding in salmon farms breeds sea lice (which can be lethal to juvenile fish), as well as other parasites and disease-causing pathogens, which also escape—right into the coastal waters where wild salmon swim en route to and from the open sea. The effect of sea lice alone could be disastrous: according to a study published last December in Science, the parasites are so ravaging opulations of one species of salmon in British Columbia that the populations are projected to plummet 99 percent within eight years.
But while the detrimental effect of salmon farms on wild fish has been known generally, the quantitative impact of swimming past salmon farms has been murkier.
Enter this study, led by Jennifer Ford of the Ecology Action Center and the late Ransom Myers of Dalhousie University. In five regions around the world, they find that the number of wild salmon surviving and returning to spawn after swimming past salmon farms is less than half the survival rate of salmon that do not get anywhere near the farms. Combined with the earlier studies, the findings point to a grim future: salmon farming is so seriously compromising natural populations that s