VANCOUVER, British Columbia, Oct. 31 (UPI) -- The precipitous drop in the sockeye salmon population in Canada's Fraser River has no simple explanation, a 1,000-page, 2 1/2-year study report concludes.
"The idea that a single event or stressor is responsible for the 1992-2009 declines in Fraser River sockeye is appealing but improbable," British Columbia Supreme Court Justice Bruce Cohen said in his final report issued Wednesday
Cohen concludes numerous factors likely have impacted the river's salmon population, including contaminants, shoreline development and ocean conditions, the Canadian Broadcasting Corp. reported.
"Climate change and warming waters present perhaps the most daunting long-term threat to the Fraser River sockeye fishery," Cohen said in his report.
Cohen makes 75 recommendations, including closing dozens of fish farms on the salmon migration route, if they're found to be too risky, the CBC said.
He also notes the risk presented by the competing responsibilities of the federal fisheries department to both promote and regulate the province's fish farms.
He recommends no new open-net salmon farm production be allowed in the Discovery Islands until September 2020.
"If by that date DFO [Fisheries Department] cannot confidently say the risk of serious harm to wild stocks is minimal, it should then prohibit all net-pen salmon farms from operating in the Discovery Islands," he wrote.
Cohen was put in charge of the investigation into the salmon population problem after only 1.4 million sockeye returned to spawn in 2009, down from the 10 million or so expected.
That year's run was followed by a massive run -- 35 million -- but the numbers fell to 4.5 million in 2011 and 2.3 million in 2012.