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Food, Health, and Eco-news
Fish Farming Update: Sea Lions Die in Fish-Farm Nets; Sea Lice Grow Drug Resistant

New reports on mammal deaths and drug-resistant lice add to aquaculture industry's woes

by Craig Weatherby

We're not opposed to aquaculture in principle. Fish farming probably is needed to supplement dwindling natural stocks of fish.

But aquaculture must be practiced more carefully, as witnessed by the continuing litany of environmental problems related to salmon farming.

Two weeks ago, we reported on violations on South American farms (see “Chile's Salmon Farms Accused of Drug and Worker Abuses”).

Now comes word that in Chile, the sea lice that afflict salmon raised on fish farms are becoming resistant to the leading pesticide.

Mortality rates caused by sea lice infestations at Chilean salmon farms are up 30 percent over last year, and the evidence suggests that sea lice have developed resistance to the lice-killing chemical emamectin benzoate.

The number of parasites per fish has increased, the treatment is less and less effective, and some farms have had to close.

The parasite does not kill the fish, but weakens them, which leads to disease and soaring death rates that make salmon farming uneconomic.

Meanwhile, marine mammals are becoming snared in Canadian salmon farms' nets.

Sea lions snared in salmon-farm nets

This past April, 51 sea lions drowned after they became trapped between nets at a Canadian salmon farm in British Columbia.

The company has reported 110 drowned sea lions so far this year, up from 46 in 2006.

Employees of Creative Salmon Company Ltd. discovered the mass of dead mammals April 12 while changing nets on the firm's Dawley Pass farm located in Tofino Inlet.

Divers initially discovered a few drowned sea lions between the grower net, which encloses the salmon, and the guard net, which is attached to the bottom of the grower net to exclude sharks.

Workers aboard a boat initially tried to remove the dead sea lions by lifting the grower net and shark guard from the water with a crane, but the load was too heavy.

Divers then entered the water and discovered dozens of dead sea lions.

The sea lions probably chewed through the predator shark guard nets to get at the salmon, but drowned when they couldn't get back out (Like whales and seals, sea lions are air-breathing marine mammals).

Environmentalists wonder how many of the limited numbers of sea lions may fall victim to B.C.'s salmon farms.

According to Catherine Stewart, campaign director for the Living Oceans Society, “We have to surmise the scope of the problem coast-wide could be very significant. You're not going to eliminate the predator [marine mammal] deaths with open net cages. Inevitably, there will be entanglements and drownings.”

She believes that the only way to avoid such deaths is to move towards closed-containment systems, a view echoed by Andrea Kavanagh, director of the Pure Salmon Campaign in a press release (Pure Salmon Campaign 2007):

“It has been a bad couple of weeks for salmon farmers around the world. First, we learned that sea lice had overrun several Chilean fish farms, forcing those companies to abandon their farms and move to new sites. And then earlier this week, the Norwegian Directorate of Fisheries revealed that in 2006, one million fish escaped from Norwegian open-net pens costing the companies $7 million. Today in Canada, Creative Salmon announced that in one incident alone, 51 California sea lions were found deaddrowned in nets that surround a single farm.

"All three incidents are tied together by a common thread. Each of these events could have been prevented if fish farmers changed their operations to physically separate their farms from the marine environment. How many more reasons do these companies need before they realize that closed containment is the way to go?

“These 51 sea lion deaths are a tragedy, but unfortunately not surprising. When fish farmers contribute to the depletion of our oceans' bait fish, marine mammals are forced to look for a new food supply. Naturally, they'll turn to a pen full of hundreds of thousands of factory farmed salmon.

“This should be a wake-up call to the aquaculture industry. Instead of continually pouring money into a broken system, it's finally time to start researching a new closed system that will be better for the planet and their pocketbooks” (Pure Salmon Campaign 2007).

The Pure Salmon Campaign is a project of the National Environmental Trust, and advocates replacing net cages with the enclosed tanks used for land-based fish farms.


  • Drews K. Creative Salmon Reports 51 Sea Lion Deaths. Accessed online June 20, 2007 at
  • Pure Salmon Campaign. Statement by Andrea Kavanagh, director, Pure Salmon Campaign, on the deaths of 51 sea lions at a Canadian salmon farm. Accessed online June 20, 2007 at
  • Science News. Farming the deep blue sea. Accessed online June 20, 2007 at