Bristol Bay sockeye thrives on diversity, UW study says

In nature, as in stock investing, the key to success is a diversified portfolio, says a new study by University of Washington biologists.

Sockeye salmon from Bristol Bay, Alaska, make up one of the world's most valuable and dependable fisheries — largely because of the variety of ecological niches the species occupies and the varied life cycles the fish have developed as a result, says a paper published Thursday in the journal Nature.

Though they're all the same species, Bristol Bay sockeye comprise hundreds of populations, each adapted to its own river, stream or tributary. Some of the populations return from the sea after one year. Others spend two years foraging in the ocean before heading back to spawn. Some sockeye flourish when it's cold and wet. Others do better in hot, dry years.

That variety means the species as a whole survives and thrives, even when bad weather or a shortage of food in the ocean hammers individual populations.

"There are enough winners to make up for the losers every year," said UW ecologist Daniel Schindler.

Humans benefit, as well. Fishermen can rely on the $120 million annual Bristol Bay sockeye harvest — as can those who relish the red-fleshed fish. The UW analysis found that if the sockeye populations in Bristol Bay were less diverse, managers would have been forced to shut down fishing every two to three years as a result of boom-and-bust cycles.

The scientists pored over 50 years of data from Bristol Bay salmon surveys and harvest records. The fish are so well-studied, it was possible to estimate how many sockeye would have returned to spawn each year for a range of theoretical scenarios where diversity was reduced: if, for example, the bay were populated only by fish that spawned after two years at sea, or if all the fish were suited only to cold, wet years.

"If you just had a homogeneous population, you would have had to close the fishery nearly every other year," said UW fisheries biologist Ray Hilborn. In reality, Bristol Bay hasn't been closed to commercial fishing since 1973.

The lesson applies broadly to other fisheries, ecosystems and even agriculture, Hilborn said. In the Pacific Northwest, salmon diversity has been slashed by habitat loss and hatcheries, which churn out monocultures of fish. But the technological fix hasn't really helped — and has in, fact, left many salmon runs more vulnerable to collapse, the scientists said.

It's important to remember, though, that hatcheries were the response to habitat destruction, said Heather Bartlett, hatcheries division manager for the Washington Department of Fish and Wildlife (WDFW). Society chose dams, agriculture and urbanization over salmon habitat. WDFW is in the midst of reforms that include scaling back hatchery production and using hatchery fish mainly to feed the appetite for sports angling.

"Hatchery reform is only going to take us part of the way," Bartlett said. "You've got to have habitat in order for these runs to rebuild."

Natural diversity is particularly crucial when disasters strike, like the oil spill in the Gulf of Mexico, Hilborn said. After the Exxon Valdez spill in Alaska, pink salmon that spawned near the shore were devastated by oil that smothered their eggs. But pinks that laid their eggs farther upstream escaped the toxic effect and were able to help the species rebound.

Before the Deepwater rig exploded and sank, the Obama administration had already decided to make Bristol Bay off-limits to offshore drilling. But the region is threatened by a proposed gold and copper mine, which could damage salmon habitat, Schindler said.

Because many previous studies of ecological diversity have been conducted in labs or on small plots, some natural resource managers have been skeptical of whether it translates into measurable benefits on a large scale, said J. Emmett Duffy, of the Virginia Institute of Marine Science. The UW study should help change that, said Duffy, who was not involved in the project.

"It's out there in the big, messy real world," he said. "And you can't get much more concrete than salmon in terms of the value to the economy."

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com