Each year, four separate "runs" of chinook salmon follow the instinctive call to work their way upstream from the ocean, through the Golden Gate to spawning areas in the Central Valley. Four decades ago, as many as 100,000 chinook -- sometimes called king salmon -- made the winter run, but with pollution and habitat degradation working against them, the winter-run population dipped to 189 fish in 1994. More recent data indicate some recovery. The chinook are thought to be a particularly sensitive indicator of the overall health of the Bay Area ecosystem because their migratory nature and range of habitat requirements make them reliant on many of its components.
NRDC researchers calculated five-year averages for the number of winter-run chinook salmon, relying on data from the California Department of Fish and Game. Averaging population figures helps researchers see beyond the effects of such short-term variables as annual weather patterns, and accounts for the chinook's spawning cycle. (The fish spawn once in their lives, usually but not always in their third year of life, and then die.) The 1995 to 1999 average of 1,874 fish was an important increase from the disastrously small 1990 to 1994 average of 487 chinook. The winter run in 1994, when just 189 chinook made the journey, was the smallest on record. In 2000, only 1,352 chinook made the winter run, a disturbingly low number. It is too soon to tell if this represents a true reversal of the positive trend of the previous five years.