Salmon farms along the Canadian coast are driving wild salmon toward extinction, according to a study published today in the journal Science. The study looked at the survival rates of wild pink salmon in British Columbia’s Broughton Archipelago, where salmon farms have sprung up along the shoreline in recent years.

Earlier studies have found that the netted pens of salmon farms are breeding grounds for parasitic sea lice, and that these lice can infect and kill young wild salmon passing by the farms. However, today’s study by fisheries ecologists at the University of Alberta and Dalhousie University is the first to show that sea lice are having population-wide impacts. If nothing is done, the scientists predict that 99 percent of the pink salmon will be gone within four years.

Sea lice attach themselves to the skin of fish and feed on their flesh. Adult fish can survive this onslaught but younger fish (such as the one pictured here) are more vulnerable because they are smaller and have thinner skin. Normally salmon encounter lice only in the open ocean where the adult fish live, but salmon farms have concentrated the lice near the rivers where wild salmon are born.

There are two possible solutions to the problem: Raise farmed salmon in self-contained pens, or move the existing pens away from the rivers and migratory routes used by young wild salmon. The fish farmers claim both options are too expensive. But losing an entire population of wild salmon would be even more costly.—Dawn Stover

Image: Alexandra Morton, Salmon Coast Field Station