Lousy With Lice

Throw another louse on the fire. A new study concludes that young Pacific sockeye salmon that migrate through coastal salmon farms carry far more parasitic sea lice than those that don’t. The finding is sure to fuel a long simmering controversy over the impact that the booming salmon farming industry is having on wild runs.

Salmon farming, which involves raising the fish in large, floating pens, has expanded in the past few decades. In some places, coastal waters are now dotted with thousands of pens holding millions of fish. The crowded conditions favor the spread of parasites and disease, and that has raised concerns that the farmed fish might pass problems along to wild runs.

In Europe and parts of North America, for example, studies have already suggested that sea lice from farms have contributed to the declines of wild salmon. Some experts worry the same trend may be playing out along Canada’s west coast, where salmon farming has grown while some of the world’s largest wild runs have declined. The problem has become so severe that, in 2009, the Canadian government opened a “Judicial Inquiry” to investigate the causes.

To see if lice might be playing a role, a team of researchers from Canadian government agencies, universities and nonprofit groups used genetic techniques to identify young sockeye salmon (Oncorhynchus nerka) originating from two major rivers: the Fraser and the Skeena. The Fraser sockeye migrate to the sea through a region with salmon farms, the Skeena fish do not. Then, the researchers compared levels of sea lice on the fish. They found that parasitism of Fraser sockeye increased significantly after the juvenile fish swam by the fish farms, and had lice levels that were an order of magnitude higher than the Skeena fish, they report in PLoS One.

The study is the first to document a possible role for salmon farms in transmitting sea lice to sockeye salmon, the authors note. And “given the high intensities of lice observed on some juveniles in this study—up to 28 lice perfish— there’s an urgent need to understand the extent of the threat,” says Craig Orr of the Watershed Watch Salmon Society, a co-author of the study. As a precaution, some conservationists have called for removing pens from key migration routes, but such ideas have sparked fierce debate in the past. David Malakoff | February 9, 2011

 Source: Price, M., Proboszcz, S., Routledge, R., Gottesfeld, A., Orr, C., & Reynolds, J. (2011). Sea Louse Infection of Juvenile Sockeye Salmon in Relation to Marine Salmon Farms on Canada’s West Coast. PLoS ONE, 6 (2) DOI: 10.1371/journal.pone.0016851

Image courtesy Raincoast Conservation Foundation