The Science of Sustainability

Where have all the salmon gone?

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Run down

Recent news headlines have been full of Chinook salmon, but sadly the same cannot be said of Central Valley waterways. This fall, only about 90,000 Central Valley Chinook salmon returned to their home rivers and streams to spawn, down from more than 800,000 just a few years ago.

Like most salmon, Central Valley Chinook are anadromous, spending the bulk of their lives in the ocean but hatching and returning to reproduce in freshwater. The journey from the Valley through the Delta and San Francisco Bay to the Pacific, and back again, has always been a long and arduous one. In the past half century it has become even more difficult as the fish have increasingly faced an obstacle course of dams, pumps, and dewatered rivers and creekbeds.

Central Valley Chinook salmon populations include four runs-winter, spring, fall, and late fall-with each spawning not only at different times of the year but in different parts of the watershed. The dawning of the age of dams hit the winter and spring runs the hardest, cutting the fish off from their historic spawning grounds in the upper reaches of the watershed. Both runs are now listed under federal and state Endangered Species Acts.


The fall run, which spawns lower in the watershed, was less impacted by dam construction. In recent decades it has numbered more than 10x all the other runs combined and has been the mainstay of the California coastal salmon fishery. Now, even it appears to be in serious trouble: The count of 90,000 salmon this year was the second lowest on record and well below the minimum conservation target of 122,000 set by the Pacific Fishery Management Council. Also alarming is that the number of 2-year-old "jacks" returning was just 2,000, down from a typical count of 40,000. Since most spawners are 3-year-olds, these early returners are considered a good predictor of the size of next year's run.

Ocean conditions are one factor in the salmon decline, with rising water temperatures and more unpredictable upwellings-possibly resulting from global warming. But scientists are also pointing to overexploitation of our rivers and Delta-the "highway" for migrating salmon. The abrupt decline in the salmon population comes concurrently with the collapse of other fish species dependent on the Delta ecosystem, including delta smelt and longfin smelt. The salmon returning to spawn this year would have been juveniles headed to the ocean in 2005, the year Delta water exports hit a record high.

Between unfriendly ocean conditions and the degraded condition of the watershed, the salmon are facing a double whammy. But, as Bay Institute Senior Scientist Tina Swanson points out, "Apart from rolling back global warming, we can't really control ocean conditions. What we can do is drastically improve conditions within the watershed so that more adults can spawn successfully and more juveniles survive the journey to the ocean."

Ann Dickinson is Communications Manager for The Bay Institute (www.bay.org), a nonprofit research, education, and advocacy organization dedicated to protecting and restoring San Francisco Bay and its watershed, "from the Sierra to the sea."

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Category: Biodiversity, Biology, Environment, Partners, Sustainable Food, Water

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Ann Dickinson

About the Author ()

Before moving to California almost five years ago, Ann served as Sally Brown Fellow in Environmental Literature at the University of Virginia, where she taught undergraduate seminars on literature and the environment and coordinated an ongoing reading series featuring nationally prominent nature writers. Prior to that, she spent a year as a research assistant at the Smithsonian Tropical Research Institute's field station on Barro Colorado Island, Panama, studying how young leaves defend themselves against herbivores.
  • Tom Edwards

    Take a look at every bay in the world anymore! Seals and Sea Lions. Thousands of them. I am thankful I don't fish and thankful that I don't like Salmon.
    Go to the mouth of any river or bay and watch the Seals and Sea Lions. One bite and throw the carcass. If they would eat them it would be better but the waste. All the crabs hang around the mouths to feast on the salmon too. Then can't catch them in traps.
    Father who was a comercial fisherman told me 50 years ago when they protected the seals and Sea Lions that the end was here for the Salmon. Too damn true!