Study shows sea lice problem widespread

Salmon farms are transferring parasitic sea lice to wild salmon over a much wider region than first thought. That’s the conclusion of a newly published article called Evidence of farm-induced parasite infestations on wild juvenile salmon in multiple regions of coastal British Columbia, Canada.

Three biologists co-authored the peer-reviewed article in the latest issue of the Canadian Journal of Fisheries and Aquatic Sciences. They are Simon Fraser University professor John Reynolds, University of Victoria professor Michael Price and Salmon Coast Field Station Director Alexandra Morton.

The study finds that fish farms are the primary source of parasitic sea lice on wild juvenile pink and chum salmon in wide swaths of coastal B.C., not just in the Broughton Archipelago.

Scientists have long correlated open net-pen salmon farms with sea lice on wild juvenile salmon in the Broughton Archipelago, a key migratory route for juvenile fish heading to the open ocean. Several studies have shown that sea lice can be fatal to small juvenile salmon.

This latest study reaffirms the correlation between sea lice in fish farms and sea lice infested wild salmon in the Broughton Archipelago region. It also establishes the link throughout the Georgia Strait, heading south, and in Finlayson Arm on the Central Coast.

“Our research underscores the value of moving open net pen salmon farms out of migration routes of wild salmon, and ultimately into land-based closed containment systems,” notes Reynolds.

The study found that in most of the regions examined, less than five-per cent of the juveniles that had not been exposed to fish farms had sea lice. In contrast, 30- to 40-per cent of fish near fish farms had the parasite.

Areas with the most fish farms, such as the Georgia Strait, had the highest infection rates of wild fish.

This study’s authors note that the highest sea lice infestation of wild juveniles is in the Discovery Islands, a region with the highest farm salmon production and through which Fraser River wild sockeye migrate.

In contrast, areas with no fish farms, such as Bella Bella, had the lowest rates of sea lice infection.