Why Massive Numbers of Farmed Salmon Are Dying


Douglas Frantz and Catherine Collins, authors of Salmon Wars: The Dark Underbelly of Our Favorite Fish, report in Time Magazine on why 865 million farmed salmon world wide have died in mass die-offs in the last decade. They cite a recent scientific study published in Nature Scientific Reports. The scientists blame the deaths on several factors, from ocean warming caused by climate change, to the aquaculture industry's overuse of antibiotics and pesticides, and its aggressive attempts to increase production. 

Franz and Collins say that, beyond the staggering number of dead fish, the findings raise questions about the future of growing salmon in cages on the ocean—and aquaculture in general.

The peer-reviewed paper published this month in Nature was the first to analyze global data on these sudden die-offs. The scientists found that these events are increasingly common and killing more fish. The data came from the four largest salmon-producing countries, Norway, Chile, the United Kingdom, and Canada, as well as two smaller producers, Australia and New Zealand.

Among the common causes were lax government regulation, competition among companies to meet rising demand, and warming waters caused by the climate crisis, Dr. Gerald Singh, an assistant professor at the University of Victoria in British Columbia and a co-author of the study, told us. "With climate change, I suspect more of these events will occur," he said.

Salmon are cold-water fish. Warm water contains less oxygen, making it harder for salmon to breathe. Marine biologists have tracked both Atlantic and Pacific salmon migrating to the Arctic in search of a more hospitable environment.

Farmed salmon, however, are trapped in cages and cannot make the journey toward colder water. Last year, when a record 17.4 million farmed salmon died in Scotland, processors blamed warming water. The deaths of 100,000 salmon at two farms off the coast of Maine were attributed to low oxygen in the water, likely a result of rising temperatures. At least 2.6 million salmon died at 10 farms along the coast of Newfoundland in eastern Canada in late summer of 2019 during a prolonged spell of warm water. An inquiry into the die-off concluded that the salmon were already under stress from chemical treatments for parasites and suffocated after swimming to the bottom of the pens in search of cooler water.

Warming waters also allow parasites and viruses to thrive inside the cages, requiring farms to use more chemicals to try to stop outbreaks that can wipe out entire farms. Rising temperatures also contribute to algal blooms, which threaten salmon by further depleting oxygen levels.

Bill Taylor, president of the Atlantic Salmon Federation, an international organization dedicated to protecting wild salmon, said the salmon farming industry is only accountable to shareholders and is focused on short-term profits. "The only way salmon farmers can really do this is to pump more fish into more cages, accept massive losses, and eke out a few more fillets at the end of a growing cycle," Taylor said in an email interview. "There is no future for salmon aquaculture in ocean sea cages."
"The increasing frequency and size of mass mortality events on open-net salmon farms is the result of an unsustainable industry operating beyond natural limits, in an increasingly unpredictable and uncontrollable environment," Rachel Mulrenan, Scotland director of the UK environmental charity WildFish, which was not involved in the study, said in an email interview.