Scientists have discovered three new viruses among endangered Chinook and sockeye salmon populations. One of the viruses belongs to a group not known to infect fish.

How the viruses affect the health of salmon isn't yet clear, but in other species, the viruses can cause serious harm.

"Although there's no risk to humans, one of the viruses is evolutionarily related to respiratory coronaviruses, and is localized to the gills," Gideon Mordecai, researcher in the department of earth, ocean and atmospheric sciences at the University of British Columbia, said in a news release. "That suggests it has a similar infection strategy to its distant relatives that infect mammals."

In a genetic survey of wild, hatchery and aquaculture salmon living along the British Columbia coast, scientists used DNA sequencing to identify the signatures of different viruses. In total, scientists sampled DNA from 6,000 salmon. The new viruses were found in hundreds of dead and dying farmed salmon, as well as in wild specimens.

"It emphasizes the potential role that viral disease may play in the population dynamics of wild fish stocks, and the threat that these viruses may pose to aquaculture," said UBC virologist Curtis Suttle.

One of the three new viruses was identified in more than 15 percent of all the tested hatchery Chinook salmon. Another was found present in 20 percent of farmed Chinook.

Researchers suggest their findings, published this week in the journal eLife, are a reminder of the evolving threats to salmon health, both in the wild and in aquaculture. The study's authors called for improved monitoring efforts and followup research to determine the health impacts of these newly identified viruses.

"It's essential that we determine whether these viruses are important factors in the decline of Chinook and sockeye salmon stocks," said Suttle. "The research highlights the need for robust surveillance to improve our understanding of how viruses might impact the health of wild Pacific salmon populations."

Over the last three decades, Chinook and sockeye salmon populations have been steadily declining. Scientists have previously identified a number of potential causes for the declines, including exposure to toxic runoff, but researchers have failed to single in on any one major culprit.

Improved monitoring efforts could help researchers protect salmon from viruses at critical points in their development, ensuring indigenous peoples, as well as commercial and recreational fishers, can continue to utilize one of the region's most prized natural resources.

"Being able to screen so many fish for these viruses was an exciting breakthrough, and meant we were able to identify hot spots of infection," said Mordecai. "One of the viruses was relatively common in juvenile migratory salmon as they enter the ocean -- a period thought to be critical to their survival into adulthood."

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