Thursday, March 19, 2009
Sacramento River's prized chinook salmon suffered a one-two punch from poor conditions in the ocean and the river, leading to the sudden collapse of the fall run, according to a study released Wednesday.
Years of losing habitat to water diversions and storage in the Central Valley so weakened the fall run that it couldn't withstand two recent years of scanty food supply in the warming Pacific Ocean, said the study by federal, state and academic scientists.
"Poor ocean conditions triggered the collapse. But what primed it is the degradation of the estuary and river habitats and the heavy reliance on hatcheries over the years," said Steve Lindley, lead author and a research ecologist at National Oceanic and Atmospheric Administration.
Over decades, construction of dams and other barriers, reliance on hatcheries and diversion of water from the Sacramento-San Joaquin River Delta have changed California's chinook salmon from genetically diverse, naturally spawning wild populations to one dominated by fall chinook salmon from four large hatcheries, the study said.
When the Central Valley had many salmon runs, the fish would migrate to the ocean at different times, increasing their odds of surviving unpredictable conditions. But the biggest remaining run, the fall run, is heavy on hatchery fish that all migrate at once and can be wiped out by poor climate and sparse food.
Last year, for the first time in California history, commercial and sport fishing was banned. Two consecutive years of low returning spawners - 87,881 in 2007 and 66,286 in 2008 - indicate that the federal regulatory body, the Pacific Fishery Management Council, will set similar curbs for this year's fishing season, which begins in May.
In a surprise finding, the study concluded that the council had a hand in the fish's sharp decline by failing to curtail fishing in 2007. Assessments show the fall-run numbers were low that year but the council didn't act.
Chuck Tracy, the council's staff management officer, agreed with the statement on Wednesday, saying the council was relying on an index used by state Department of Fish and Game and National Marine Fisheries Service. The council has since adopted a new forecast method.
Here's what happened to the fish, according to the study:
Salmon hatched in the Sacramento River and its tributaries in 2004 and 2005 entered ocean feeding grounds months later in 2005 and 2006 during periods of warm sea-surface temperature.
In 2005, ocean studies found malnourished salmon, seabirds and marine mammals. Weak winds from the north and weak mixing of ocean layers quelled the upwelling of nutrients from the depths that feed the food chain, the study said.
Representatives of environmental and commercial fishing groups said the study ignored the need for freshwater flows for the fish to get through the delta to the bay and the ocean.
"We know in past years that higher levels of pumping, under below-normal or dry conditions, took a real toll on Central Valley salmon stocks, and that is exactly what we had going on in 2004 and 2005," said Zeke Grader, executive director of Pacific Coast Federation of Fishermen's Associations.
Tina Swanson, executive director of the Bay Institute, a Novato science center, said the scientists should call for reforms in the way water is released in the Central Valley, including requiring Shasta Dam to release cold water for salmon and the Red Bluff dam to leave its gates open for fish.
"These agencies know what needs to be done but there has been a real lack of will on their part to require and enforce these actions," she said.