Simon Fraser University

Sea lice studies reveal flaws

January 26, 2006 , vol. 35, no. 2

By Carol Thorbes
There are serious flaws in the way the federal department of Fisheries and Oceans assesses the potentially lethal effects of sea lice on juvenile salmon, according to a research paper co-authored by Rick Routledge, a fish population statistician at Simon Fraser University's centre for coastal studies.

For the past three years, he and co-author Alexandra Morton, an independent fish biologist, have been studying the impact of sea lice-infested fish farms on migrating young salmon in the Broughton Archipelago.

“I believe that most of the very young pink and chum salmon that pass by fish farms soon after they enter salt water will die if they're exposed to the high infestation levels that we've observed in the Broughton Archipelago in recent years,” says Routledge.

The duo's previous studies showed that pink and chum salmon are covered in sea lice after migrating past fish farms. Now, their latest research reveals that a Fisheries and Oceans Canada fish health assessment method, called the Fulton condition factor (FCF), is so flawed that it fails to recognize when sea lice are killing fish until just days before the fish die. The FCF method gives fish a clean bill of health if their weight corresponds to a form of height-to-weight ratio index for good health.

Their research shows that sea lice-infested juvenile pinks and chum maintain a healthy weight until shortly before a behavioural change and then die quickly. “They become listless, fail to respond to mock predatory threats and drift away from their school,” says Routledge.

“Because this abnormal phase is so short-lived, they are never abundant in the population. It's analogous to people with heart disease. Even though many people die of heart attacks every year, you don't see many people suffering from heart failure as you walk the streets. The trauma is too short-lived.”

Routledge and Morton say that once sea lice-infested juveniles become emaciated, they will soon die even if predators don't catch them. Consequently, federal scientists never catch many samples of emaciated, sea lice-infested fish to put through their FCF test. The duo concludes: “The Fulton Condition Factor is not a reliable indicator of the impact of sea lice infestations on juvenile pink and chum salmon.” The study, Fulton's Condition Factor: Is It a Valid Measure of Sea Lice Impact on Juvenile Salmon?The North American Journal of Fisheries Management available online here. Routledge and Morton now want federal scientists to stop using the FCF to assess infested fish.

They also want the province to re-impose its previous moratorium on fish-farm expansion and to move farms away from areas used by the youngest and most vulnerable wild salmon.