Whither the run?
Scientists try to explain dismal salmon run
Jane Kay, Chronicle Environment Writer
Monday, March 24, 2008
Amid growing concern over an imminent shutdown of the commercial and sport chinook salmon season, scientists are struggling to figure out why the largest run on the West Coast hit rock bottom and what Californians can do to bring it back.
The chinook salmon - born in the rivers, growing in the bay and ocean, and returning to home rivers to spawn - need two essential conditions early in life to prosper: safe passage through the rivers to the bay and lots of seafood to eat once they reach the ocean.
Yet, the Sacramento River run of salmon that was expected to fill fish markets in May didn't find those life-sustaining conditions. And some scientists say that's the likeliest explanation for why the number of returning spawners plummeted last fall to roughly 90,000, about 10 percent of the peak reached just a few years ago.
The devastating one-two punch happened as the water projects in the Sacramento-San Joaquin River Delta pumped record amounts of snowmelt and rainwater to farms and cities in Southern California, degrading the salmon's habitat. And once the chinook reached the ocean, they couldn't find the food they needed to survive where and when they needed it.
"You need good conditions in the rivers and ocean to get survival and good returns for spawning," said Stephen Ralston, supervisory research fisheries biologist with the National Oceanic and Atmospheric Administration, or NOAA, and a science adviser to the Pacific Coast Fishery Management Council.
Without those favorable conditions, the salmon run crashed. Five years ago, the peak was 872,700 returning spawners. Roughly 90,000 were counted in 2007, and only 63,900 are expected to return to spawn in fall 2008.
Helped by cool-water winter
The fishery council, a regulatory body charged with setting fishing limits, has recommended a full closure or a strict curtailment of the commercial and sport season. A final decision will come in April.
NOAA researchers say a cool-water winter will help the beleaguered run in the future. An influx of cold Alaska waters, along with a shot of nutrients from vigorous upwelling of deep waters, have been fueling the food chain that feeds salmon, birds and marine mammals.
But the scientists warn that chinook, which have swum through the San Francisco Bay for thousands of years, have suffered human harm over the past half-century and now also need human help.
They've proposed a number of solutions, including sending more water over the dams and reservoirs and down the tributaries where salmon spawn; removing barriers to migration such as old dams; screening the fish away from the pumps and diversion pipes that suck them up, misdirect or kill them; controlling pesticide and sewage pollution - and catching fewer fish while the populations try to rebuild.