Normally when you think of lice, you have images of children getting their hair examined by a school nurse with a wooden tongue depressor. But fish farms on Canada’s west coast are infested with sea lice that could threaten the wild salmon population. The infestation is so severe that researchers are hypothesizing that it could lead to extinction in four year.

For about forty years researchers in Canada have been looking at wild salmon populations who have had exposure to the farm raised variety. By looking at rivers in British Columbia, they can compare differences in fish that have had exposure to that who haven’t. "The results are striking. Overall the populations that were not exposed to sea lice disease are stable or increasing," said Martin Krkosek, a fisheries ecologist from the University of Alberta in Edmonton, whose study appears in the journal Science. Krkosek also said this is the same for commercial fishing as well. "Overall, populations that were exposed to sea lice-diseased salmon farms are depressed and are declining quickly. This was true even though commercial fishing was closed on these populations," he said.

Sea lice are parasites that attach themselves to the skin of the fish as they make their way from rivers to the sea. The lice feed on the skin and muscle of the fish. Older fish are usually hearty enough to fight off the infection, but young fish are not. In nature the young fish can avoid it because the infected adults are offshore. The farm raised variety are not so lucky because they feed into rivers through open net systems can expose young salmon swimming past them to the disease.

This study is bringing light to the dwindling numbers and researchers are looking for solutions. The solution is simple," Alexandra Morton, director of the Salmon Coast Field Station in Broughton, told reporters in the briefing. "Build a better barrier to separate the older salmon from the younger salmon."