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Chapter 6 -- Changes and Trends in Stream Habitat and Fisheries (continued)

Influence of Marine Conditions

Salmon productivity is highly dependent on productivity in the marine environment. Survival of smolts in the ocean is greatly influenced by upwelling ocean currents. The success of a particular year class is heavily influenced by the amount of upwelling during their first six months of ocean residence (McCain et al. 1995). If upwelling is limited, an entire year class may be curtailed.

Overall productivity of the marine environment appears to vary in a predictable pattern over decades. Evidence is accumulating that sea surface temperatures vary in a 50 to 70 year cycle as part of an oscillating pattern in the climate of the North Pacific. This pattern, which has occurred for the last 300 years, has opposite effects on sockeye and pink salmon populations in Alaska compared to spring chinook and coho salmon populations in Oregon, Washington, and California. It is believed that cyclical changes in sea surface temperature, occurring as part of global atmospheric and oceanic patterns, affect the entire food chain in nearshore waters from phytoplankton and zooplankton to salmon. When the waters of the North Pacific are colder, the nearshore waters from Washington to southern California tend to be warmer and vice versa. In areas where ocean water temperatures on the ocean surface are colder, productivity of the marine food chain including salmon tends to be higher. Cold ocean temperatures are generally correlated with high streamflows that also benefit salmon. When the Alaskan salmon are abundant, salmon in California, Oregon, and Washington are reduced and vice versa. Reversals in the pattern occurred in 1925, 1947, and 1977, on an average of about 20 to 35 years. Currently the pattern is unfavorable for salmon in California, Oregon, and Washington. The next reversal will probably happen between 1999 and 2012. The pattern is not absolute; there are occasional three year periods that go against the overall trend. It is likely that trends are only detectable in hindsight (Mantua et al. 1997).

This pattern in the North Pacific interacts with the El Niño-Southern Oscillation which primarily effects tropical regions. Although researchers have found a relationship between the oscillation in the North Pacific and the abundance of salmon, they have not found a significant relationship between Pacific salmon abundance and El Niño. This may be due to the more frequent fluctuation of El Niño that does not last long enough to be reflected in trends in salmon populations over decades (Mantua et al. 1997). Furthermore effects of the El Niño-Southern Oscillation are variable in northern California and so effect on anadromous fish probably varies as well.

Productivity in the nearshore waters of California, Oregon, and Washington may increase in coming years due to an expected change in ocean conditions related to the reversal of the climatic oscillation in the North Pacific. Until that happens, coho and spring chinook populations in these areas may be incapable of rapid recovery. Low productivity in the marine environment makes it more difficult to save sensitive anadromous salmonid stocks from extinction.

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