British Columbia

New research suggests wild salmon exposed to fish farms have 'much higher' rate of viral infection

Fraser River sockeye and chinook salmon pass through some of the most dense fish farming areas and were found to have high rates of infection compared to wild salmon in the north where fish farms are not a factor.

Wild salmon infected with the virus struggle to return to spawning grounds, says report's author

Alexandra Morton is lead author on a report that says wild salmon exposed to open-net fish farms are much more likely to be infected with piscine reovirus (PRV). (Sea Shepherd Conservation Society)

Wild salmon exposed to open-net fish farms are much more likely to be infected with piscine reovirus (PRV) than those that don't have that contact, a new study has concluded.

The data also show that the virus makes it more difficult for wild salmon to swim upstream to their spawning grounds, which has major implications for the sustainability of the populations.

"The government has to remove this industry from the key salmon migration routes or we risk the complete loss of wild salmon in this province," said Alexandra Morton, lead author on the report and an outspoken advocate for wild salmon.

Major implications for Fraser sockeye, chinook

​According to the research, PRV was found to be much more prevalent in the lower Fraser River than the upper Fraser River.

"This suggests that salmon infected with PRV are less capable of swimming up through strong rapids in places like Hell's Gate and therefore unable to reach their spawning grounds," said co-author Rick Routledge, a professor of statistics at Simon Fraser University. 

The study showed a 37-per-cent rate of infection of wild salmon in the Discovery Islands and 45 per cent in wild salmon in the Broughton Archipelago.

Both areas have a high density of farming activity.

Important commercial fish populations run through the area, including Fraser River sockeye and chinook, which are an essential part of the diet of southern resident killer whales.

The Discovery Islands were the focus of the 2012 Cohen Commission, which concluded that fish farms were likely having a serious impact on Fraser River sockeye, which pass through the area on their journey back to the Fraser.

"Nobody has looked at this and these fish are collapsing," said Morton who worries that because the virus is believed to have originated in Norway, native species do not have a natural defence against the infection.

Detected in wild trout

The virus was found in both wild salmon and trout, such as steelhead, which have also featured dramatic decreases in annual returns in recent years.

The study examined fish in the Broughton Archipelago, where First Nations have recently occupied fish farms in protest of the practice of open-net farming.

"The difference between the infection level in wild fish in the north and south was absolutely startling," said Morton.

Salmon stocks in the Fraser, Skeena and Nass have all seen record low returns in 2017 though scientists point to a number of factors including warming oceans, increasing river temperatures, predation and loss of habitat as contributing factors.

The research is the first of its kind to conclude that large numbers of B.C's wild salmon are becoming infected with PRV through exposure to fish farms.

PRV is a virus that causes an acute infection in the red blood cells of the fish, which reduces oxygen levels.

Industry disputes suggestions of harm

In Norway, the local strain of the virus has been linked to a deadly salmon disease called Heart and Skeletal Muscle Inflammation, or HSMI.

HSMI has been documented on a fish farm in this province, but any connection to PRV has yet to be established, and Fisheries and Oceans Canada says the evidence in this country suggests the B.C. version of the virus has a "low ability to cause disease."

Researchers here have tried exposing Pacific and Atlantic salmon to the B.C. strain of PRV in controlled experiments, but none of the fish have fallen sick or died, according to the federal ministry.

Those in the fish farming industry say they're not convinced the virus causes any illness in salmon.

"Our members aren't considering any direction actions on their farms," said Jeremy Dunn, executive director of the B.C. Salmon Farmers Association.

"This virus is well known to be common amongst farm fish for many years. It is not associated with any sickness with the fish on our farms, and this paper in particular ... hasn't provided any direct evidence that there's any harm being caused."

Still, the scientists behind the new report worry that long before a fish develops HSMI, the effects of the virus weaken fish to the point they cannot make it back to their spawning grounds, which require swimming long distances upstream.


  • A previous version of the story misstated the link between piscine reovirus and Heart and Skeletal Muscle Inflammation.
    Dec 14, 2017 7:21 AM PT