Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

Oceanographic Features and Climatic Variability
Oceanographic features of the action area may influence prey availability and habitat for
Pacific salmonids. The action area includes important spawning and rearing grounds and
physical and biological features essential to the conservation of listed Pacific salmonids -
i.e., water quality, prey, and passage conditions. Ocean conditions and climatic
variability may affect salmonids in the action area.
The primary effects of the ocean on salmon productivity involve growth and survival of
salmon. All salmon growth is completed in the ocean. According to Welch (1996), fish
growth will not reach its maximum potential if food density (food available divided by
ocean volume) is insufficient to provide the maximum daily ration. If this critical level of
food is not exceeded, then the potential for the ocean to limit salmon growth exists.
The decline in salmon survival in Oregon and Washington since 1977 may be caused by
poorly understood processes in the marine (as opposed to freshwater) environment
(Welch 1996). Current findings also indicate that the primary control on salmon
distribution is temperature. However, the upper thermal limit varies throughout the year
(Welch 1996).
Naturally occurring climatic patterns, such as the Pacific Decadal Oscillation and the El
Niño and La Niña events, are major causes of changing marine productivity. Recent
studies have shown that long-term changes in climate affect oceanic structure and
produce abrupt differences in salmon marine survival and returns (Mantua, Hare et al.
1997; Hare, Mantua et al. 1999). A major regime shift in the subarctic and California
Current ecosystems during the late 1970s may have been a factor in reducing ocean
survival of salmon in the Pacific Northwest and in increasing the marine survival in
Alaska (Hare, Mantua et al. 1999). Fluctuations in mortality of salmon in the freshwater
and marine environment have been shown to be almost equally significant sources of
annual recruitment variability (Bradford 1997). These events and changes in ocean
temperature may also influence salmonid abundance in the action area. In years when
ocean conditions are cooler than usual, the majority of sockeye salmon returning to the
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