Atlantic salmon face perilous waters.

Although Canada's west coast is well known for disputes over the beleaguered Pacific salmon, it was the country's East Coast salmon fisheries - wild salmon in the north Atlantic Ocean and farm-raised salmon in New Brunswick - that made headlines last summer. Early in 1998, the salmon population in the North Atlantic Ocean dropped to 114,000 mature fish - its lowest point ever and barely half of what experts say was needed to meet minimum spawning targets. Meanwhile, salmon farmers in the Canadian province of New Brunswick were faced with the opposite problem: they couldn't seem to kill their crop fast enough to stop the spread of disease. Since March 1998, New Brunswick salmon growers have slaughtered more than 1.2 million salmon under provincial government orders in an effort to contain an outbreak of Infectious Salmon Anemia (ISA).

With the North Atlantic salmon fishery on the brink of collapse, all seven countries in the North Atlantic Salmon Conservation Organization (NASCO) in June 1998 agreed to a moratorium on commercial salmon fishing. While the ban alleviates one part of the problem, it leaves another critical part unaddressed: some of the most serious pressures on Atlantic salmon come not from fishing, but from pressures on spawning grounds. Rivers from Maine to Quebec have been blocked by hydroelectric dams and contaminated with effluent from pulp and paper mills for decades. The task of rehabilitating wild salmon stocks has been further complicated by the growing presence of salmon netcages for the fish farms that dot coastal waters. Farmed salmon can choke waters with their waste, dilute the genetic diversity of wild salmon through escaped fish, and transmit diseases to wild salmon.

In the farmed-salmon sector, about one-fourth of the industry was shut down for the 1998 season by the ISA epidemic. The disease, which suppresses the immune system and leaves the fish vulnerable to infection, exists at low levels in the wild. It was first detected in the Bay of Fundy more than a year ago and has since flared up, apparently thriving in the breeding grounds offered by the netcages that hold densely packed salmon under intense feeding and growing regimes.

Once ISA or another disease takes hold in a fish farm, the fear is that it may spread uncontrollably and infect wild fish, invertebrates, seabirds, and perhaps even people. In fact, Scottish scientists have confirmed that thousands of wild sea trout in Northwest Scotland have been killed by diseases originating in commercial salmon farms. In response, infected salmon have been doused with chemicals to rid them of sea lice, one of the vectors that transmit ISA. However, some sea lice have developed a resistance to the pesticides, which may Icad authorities to approve more toxic substitutes.

Arguably, these drastic measures could have been avoided, as these recent episodes are merely repeats of history: ISA outbreaks in the late 1980s and early 1990s in Norway cost an estimated $100 million in economic losses. Rather than advocating the widespread use of toxic chemicals, officials in New Brunswick are requiring growers to incorporate cleaner operations - lower densities of fish, greater distance between cages, and improved effluent treatment. Whether these measures will be implemented quickly enough to control the spread of the disease remains to be seen. Because salmon need a healthy environment, protecting them requires sound management on an ecosystemwide basis.