Two researchers hired by the Cohen Inquiry have come to differing conclusions on the likelihood commercial salmon farms are seriously harming the Fraser River sockeye run.
SFU biologist Larry Dill concluded the evidence suggests the growth in fish farm production and the decline in sockeye stocks are linked, likely in concert with other marine factors.
He found the spread of disease is the most likely factor – not sea lice infestations, escaping farmed salmon or waste discharged from the farms, such as uneaten food or chemicals.
The potential damage to juvenile sockeye from the large numbers of penned Atlantic salmon they pass in the Broughton Archipelago might seem like common sense, Dill testified Monday before the commission into the decline of sockeye stocks, but stressed his findings are far from conclusive.
"The evidence for that is there, but it's fairly weak and uncertain," he said. "Common sense is not always a good guide to science."
Dill said the aquaculture industry adds new risks for migrating wild stocks.
The farms make it much easier for different incoming or outgoing generations of sockeye to pass pathogens back and forth, he said.
Dill also said the huge number of fish being farmed leads to bio-magnification, where large numbers of parasites can build up, and more virulent strains of pathogens can evolve.
Don Noakes, a Thomson Rivers University professor, penned a second paper commissioned by the inquiry, and concluded none of the risk factors associated with fish farms is likely to have damaged sockeye runs and found no link between them.
He said he has concerns about the interpretation of data from studies examining the possible link between sea lice and salmon in the Discovery Islands, which he called unlikely.
"There is no evidence that any exotic pathogens or diseases have been introduced by the salmon farming industry," Noakes report states.
In cross-examination before the commission Monday, Noakes was pressed to admit his findings were "speculative" and water them down.
"It's my assessment," he maintained. "I haven't heard anything to convince me otherwise."
The inquiry heard that three million Atlantic salmon die each year in the floating net pens between northern Vancouver Island and the mainland, and that up to 600,000 perish from disease.
Previously, the inquiry heard geneticist Kristi Miller argue a newly detected virus could be a major factor behind the sockeye die-off, but she also conceded the evidence so far does not suggest aquaculture is directly responsible.
Dill, Noakes and two other researchers testifying Monday agreed that wild sockeye and the aquaculture industry should be able to safely co-exist, if the farms are managed properly and steps are taken to reduce any harmful interactions between them.
Lawyers for the provincial government agreed Monday to release provincial audits of salmon farms, including data on dead and diseased fish.
That was a reversal from last week, when the provincial representative at the inquiry argued the release would not be in the public interest and could have a chilling effect on voluntary disclosure of disease outbreaks – on livestock farms as well as fish farms.
"I don't think anybody bought that," said Watershed Watch Salmon Society executive director Craig Orr, who said the provincial concession was a relief to many inquiry participants.
"It's really important to have the audited data to examine to see whether there are problems in the data submitted by the farmers."
Aquaculture remains the focus of the sockeye commission hearings until at least Sept. 8, before turning to issues such as water temperatures, cumulative impacts and the priorities of the Department of Fisheries and Oceans.
The judicial inquiry led by retired Judge Bruce Cohen was called by the federal government after less than 1.5 million sockeye returned in 2009, far fewer than the more than 10 million expected.