The industry responded by stuffing, on average, twice as many fish into each farm. Today, farms typically put 50,000 to 90,000 fish in a pen 100 feet by 100 feet. A single farm can grow 400,000 fish. Others raise a million or more.
The moratorium on new farms was lifted in September by the provincial government after voters elected a pro-business slate of lawmakers and administrators. As a result, 10 to 15 farms are expected to open each year over the next decade.
Five international companies -- three of them based in Norway -- control most of the existing farms. Nearly all are situated around Vancouver Island, which begins outside Seattle's Puget Sound and extends up the coast for 300 miles.
It's a lightly populated place of stunning beauty. Cedar, hemlock and Douglas fir grow right down to the high-water mark.
Massive tides flush rich blue-green waters through the archipelago of islands, straits, bays and inlets, nurturing five types of wild salmon. These, in turn, attract seals, sea lions, white-sided dolphins and the world's best known pods of killer whales.
Residents rely on boats and seaplanes to reach surrounding islands that host many of the farms. Each farm is a cluster of pens, often interconnected by metal walkways and tethered offshore by a lattice of steel cables, floats and weights.
In the midst of this idyllic setting, signs of strain on the marine environment are bubbling to the surface much the way diseases and parasites, incubated in European salmon farms, fouled the fiords of Norway and the lochs of Scotland.
In Norway, parasites have so devastated wild fish that the government poisoned all aquatic life in dozens of rivers and streams in an effort to re-boot the ecological system.
"The Norwegian companies are transferring the same operations here that have been used in Europe," said Pauly, the fisheries professor. "So we can infer that every mistake that has been done in Norway and Scotland will be replicated here."
Dale Blackburn, vice president of West Coast operations for Norwegian-based Stolt Sea Farm, said his staff works very closely with its counterparts in Norway. But, he said, "It's ridiculous to think we don't learn from our mistakes and transfer technology blindly."
Still, more than a dozen farms in British Columbia have been stricken by infectious hematopoietic necrosis, a virus that attacks the kidneys and spleen of fish.
Jeanine Siemens, manager of a Stolt farm, said, "It was really hard for me and the crew" to oversee the killing of 900,000 young salmon last August because of a viral outbreak.
"We had a boat pumping dead fish every day," she said. "It took a couple of weeks. But it was the best decision. You are at risk of infecting other farms."
Farms are typically required to bury the dead in landfills to protect wild marine life and the environment. But Grieg Seafood recently got an emergency permit from the Canadian government to dump in the Pacific 900 tons of salmon killed by a toxic algae bloom. The emergency? The weight of the dead fish threatened to sink the entire farm.
About 1 million live Atlantic salmon -- favored by farmers because they grow fast and can be packed in tight quarters -- have escaped through holes in nets and storm-wrecked farms in the Pacific Northwest.
Biologists fear these invaders will out-compete Pacific salmon and trout for food and territory, hastening the demise of the native fish. An Atlantic salmon takeover could knock nature's balance out of whack and turn a healthy, diverse marine habitat into one dominated by a single invasive species.
Preserving diversity is essential, biologists say, because multiple species of salmon have a better chance of surviving than just one.
John Volpe, a fisheries ecologist at the University of Alberta, has been swimming rivers with snorkel and mask to document the spread of Atlantic salmon and their offspring.
"In the majority of rivers, I find Atlantic salmon," Volpe said. "We know they are out there; we just don't know how many, or what to do about them."
His research focuses on how Atlantic salmon can colonize, if given a chance. It has terrified the U.S. neighbors to the north. Alaskan officials banned fish farms in 1990 to protect their wild fishery. So they don't take kindly to British Columbian farms creeping toward their southern border.
Although native Pacific salmon are rare and endangered in the Lower 48, Alaska's salmon fisheries are so healthy they have earned the Marine Stewardship Council's eco-label as "sustainable." The council's labels are designed to guide consumers to species that are not being overharvested.
Recently, the prospect of genetically modified salmon that can grow six times faster than normal fish has heightened anxiety. Aqua Bounty Farms Inc., of Waltham, Mass., is seeking U.S. and Canadian approval to alter genes to produce a growth hormone that could shave a year off the usual 2 1/2 to three years it takes to raise a market-size fish.