Bristol Bay sockeye thrive on diversity, scientists say

June 2, 2010 

SEATTLE -- A new study says that sockeye salmon from the five river systems of Bristol Bay make up a valuable and dependable commercial fishery largely because of the variety of ecological niches the species occupies and the varied life cycles the fish have developed as a result.

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

Opponents of developing the Pebble copper and gold deposit in headwaters of two of Bristol Bay's five river systems were touting the new study as part of their campaign to block development of a multibillion-dollar Pebble mine, saying a mine accident could upset the salmon ecosystem.

The study said that although 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.

50 YEARS OF STUDY

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. 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.

LESSONS FOR FISHERY MANAGERS

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 place an area through which Bristol Bay salmon migrate off-limits to offshore drilling. Developing the Pebble mine could damage salmon habitat, Schindler said. He has made public statements opposing Pebble development in the past, based on his research.

The mining companies pursuing Pebble have said state regulators will thoroughly assess any development plan and vow that "protection of the area's ecosystem is a critical element of success" for Pebble.

Jeff Hutchings, a wildlife biology professor at Dalhousie University in Canada who was not involved with the research, called it "groundbreaking."

"It's the strongest evidence to date that there's a financial benefit to maintaining population diversity," he said. "If managers ignore this, they do so at their own peril."


The Anchorage Daily News/adn.com contributed to this article.

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