Researchers who have spent the past two decades studying one of the most productive salmon fisheries in North America say "techno" fixes like hatcheries could be doing more harm than good to salmon populations.

Ray Hilborn and Daniel Schindler, both from the University of Washinton, looked at 50 years of data from the Bristol Bay salmon fishery in Alaska. They found that its success was due to what they called a "portfolio effect". Because there are a variety of different populations within a salmon species, there's a greater chance that at least one of those populations will be a "winner" based on the particular conditions of any given year.

"Some respond better in cold, wet years, others in warm and dry years," said Schindler. "The net result is that each population experiences its own ups and downs based on environmental conditions and pure chance. The winner makes up for the loser every year."

Their findings were published in a paper that made the cover of this month's Nature magazine. Schindler says that, while scientists have long known that ecological diversity offers more stability (and is even more important in the face of climate change) biodiversity within a species is often overlooked.

Within the Fraser River, for example, there are dozens of different species of sockeye that hatch and spawn in different streams. The Fraser and the Skeena are Britsih Columbia's two greatest salmon rivers, and although the Fraser especially has lost many of its returning fish, it's not too late to save them, say the researchers.

"We have already lost about 30 per cent of population diversity native to the west coast," says Schindler. "But. . . populations still exist. B.C. is in the enviable position of being able to protect diversity."

How? "Don't judge value by recently productivity," said Hilborn. "Be prepared for surprises. Don't let hatcheries put all their eggs in one basket by producing one species that dominates productivity. Keep harvest pressure lower than would appear." And, most importantly, work aggressively to protect salmon habitat.

"If we allow the salmon biology to play out as it should. . . these stocks will probably re-diversify, assuming they aren't swamped by hatchery fish," said Schindler. "The biggest unknown as we look to the future is what climate change will do. If river become too warm, all bets are off."

Colleen Kimmett reports for The Tyee.