Something To Think About: Confirmation Bias

December 5, 2017 - Campbell River, B.C.

By Ian Roberts, Director of Public Affairs, Marine Harvest Canada

Every now and then I receive an email with a link to a peer-reviewed study about salmon farming and a question along the lines of “What is your response to this study that proves what I think?”

This is confirmation bias, selecting science papers that agree with your preconceived ideas. We are all guilty of it. My response could easily be “Well, here’s a study that proves what I think.”

However, in the last decade, several thorough science reviews specific to B.C. salmon farming have occurred in attempt to eliminate confirmation bias.

Cohen Commission, 2012

The $35M Cohen Commission reviewed thousands of documents and interviewed hundreds of witnesses to understand impacts to the Fraser River sockeye. The Commission concluded the following (ranked in order) as primarily affecting Fraser sockeye: 1. Ocean conditions inside and outside Georgia Strait; 2. Delayed density dependent mortality (another way of saying natural “boom and bust” but over a long time scale); 3. Competitive interactions with pink salmon; 4. Marine and freshwater pathogens. Specific to salmon farming the Commission concluded that: “Data presented during this Inquiry did not show that salmon farms were having a significant negative impact on Fraser River sockeye.” (Final Report, Vol 3, page 24).

Senate Inquiry, 2015

The Canadian Senate Committee on Fisheries and Oceans issued its report called An Ocean of Opportunities: Aquaculture in Canada. The Committee sat for 66 hours, held 34 public hearings, heard the views of 138 witnesses, and received hundreds of written submissions and other documentation. Senators also visited 23 Canadian regions in 6 Provinces. The report concluded that Canadian aquaculture research and development is internationally recognized for its high quality and recommended that aquaculture production should be doubled within the next 10 years, provided that operators adhere to environmentally-sound practices. You can read the final reports online.

Monterey Bay Review, 2017

Monterey Bay Aquarium’s Seafood Watch program published its review of available science on B.C. salmon aquaculture. The report states that while a level of concern may be warranted, “there is currently no evidence that there is any impact from salmon farms to wild salmon.” Seafood Watch ranks farmed Atlantic salmon raised in marine net pens in B.C. to consumers as a “good alternative”. The full report is published at

Instead of arguing that “my study is truer than yours” or “my biology degree is better than your PhD”, I point to these comprehensive science reviews. They’ve been led by a judge, the government, and a non-government environmental organization and they assess a broad range of studies to eliminate confirmation bias.