|<< Upwelling Front Page | << Previous Article in Upwelling (2 of 4) | Next Article in Upwelling (4 of 4) >>|
Where Have all the Salmon Gone?
By Nate Grader
Prior to the Gold Rush, Chinook salmon, the most highly prized and largest of the Pacific salmon, returned to spawn in the Sacramento and San Joaquin Rivers in California’s Central Valley in almost unimaginable numbers. The unique combination of enormously productive upwelling currents off the California coast and the year round cold but largely ice free tributaries in the Central Valley produced massive Chinook runs.
An estimated historical abundance of around ten to fifteen million fish (from four genetically distinct Chinook runs) returned annually through the San Francisco Bay and delta to their spawning grounds that once stretched past Redding to the north, Auburn to the east and Fresno to the south.
Only the Columbia River on the West Coast surpassed the Sacramento and San Joaquin Rivers and their tributaries in terms of salmon productivity. Early settlers famously described returning salmon so thick that one could “walk across the backs of salmon” to cross a river and not get wet.
Today, nearly all of the major tributaries of the Sacramento and San Joaquin Rivers are truncated by dams. These dams are part of California’s complex hydrological infrastructure that sends a large portion of water from the Sacramento and San Joaquin Rivers to farms and urban centers through a system of pumps and canals.
Rivers, such as the McCloud River above Shasta Dam, whose year round cold water once supported four runs of Chinook, are now irrevocably cut off from spawning salmon. Add to that 150 years of poor land use practices, including hydraulic gold mining during the Gold Rush, and a myriad of other factors –pollution, invasive species, unscreened diversions –and the remaining habitat is not nearly as productive as it once was. Along with the loss of spawning habitat (around 95 %) and degradation to the remaining habitat has been a corresponding loss in salmon abundance.
Salmon runs, largely supported by hatcheries at the base of dams throughout the Sacramento and San Joaquin River system, had stabilized to an average annual abundance ranging from half a million to over a million fish by the end of the 20th century. Additionally, because of hydrological changes to the river system, the most abundant run is now the fall run, historically the smallest run and least favored by native fishermen and early European fishermen because of its lower fat content. During the winter run and spring run, Chinook salmon’s numbers are so low that they are now protected under the Endangered Species Act.
Despite all of these losses, the California Central Valley salmon still support a sustainable fishery valued at $100 million a year that has been the lifeblood for coastal fishing communities from Santa Barbara to central Oregon (60% of the commercial and recreational catch originates from the Central Valley). However, this year’s returns of Central Valley salmon were drastically lower than expected.
Fishermen were the first to notice that salmon abundance was lower than expected as they spent long hours trolling the coast along their favorite tacks with few salmon to show for their effort. Many fishermen report the 2007 season to be the worst they have ever seen. This year’s commercial salmon season, stretching from April to October punctuated by closures to reduce pressure on threatened stocks, was especially frustrating for commercial fishermen given that it was supposed to be a good season.
The “missing” salmon run has left fishermen frustrated and scientists and fisheries managers looking for answers. Everyone seems to have their own theory. Fisheries managers blame ocean conditions such as changes in currents and krill abundance two years ago which would explain the lack of adult 3 and 4 year old salmon this year. Some have postulated the invading Humboldt squid may be decimating young salmon. Still others think that poor hatchery practices combined with invasive species in the delta have led to a poor return of Central Valley salmon.
One explanation that everyone seems to agree on is that the record high water exports in the last few years from the delta are somehow tied to the low salmon returns. The delta smelt, an important indicator species (the canary in the coal mine) for the overall health of the delta ecosystem, is on the verge of extinction because of the record high water exports.
As policy makers and politicians haggle over water exports from the delta, conservationists and fishermen fear that the remnant of a once magnificent run of salmon and a commercial fishing industry hangs in the balance.
|© 2005-2006 Farallones Marine
All Rights Reserved.