145 



8 



River. Perhaps 14 percent of all migrating juvenile salmonids in the John Day Pool of the 

 Columbia River are eaten by fish predators. 



Seals and sea lions have been protected by the Marine Mammal Protection Act since 1972. 

 Harbor seal and California sea lion populations in Pacific Northwest marine waters have steadily 

 increased between 4 and 12 percent per year. Based on population estimates and gut and scat 

 analysis, seals and sea lions in Oregon and Washington waters may have consumed a combined 

 8 million pounds of salmon (about 1 million fish) in 1990. This was equivalent to about 17 

 percent of the two state's combined commercial salmon catch of 5.6 million fish in that year. 

 Seals and sea lions also injure fish. Recent studies estimated that almost 20 percent of salmon 

 ascending Columbia River dams had "seal bites". Such wounded fish are more vulnerable to 

 disease infection and death and this might help explain part of the 50 percent indirect mortality 

 of upstream adult migrants not accounted for by direct structural losses at Columbia-Snake River 

 dams. 



Significant flood plain riverine habitat and estuary habitat has been lost in Oregon and 

 Washington. Because of these habitat losses, food chain production in the Columbia Estuary has 

 shifted from a macrodetritus base, primarily derived from marsh and swamp vegetation, to a 

 microdetritus base derived from phytoplankton. Similar changes have probably occurred in other 

 coastal rivers and bays. Amphipods and isopods (invertebrates) are detrital feeders and important 

 prey for juvenile salmonids. Significant production of these invertebrates has been lost because 

 of the change in the food base. Insect production from marshes and swamps has been reduced 

 proportionate to area losses. Insects are also important prey for juvenile salmonids. There is a 

 strong implication that food supply may now be limiting in the Pacific Northwest in the area of 

 river mouths and coastal bays. This is probably aggravated by large releases of hatchery fish. 

 In 1990, hatchery releases in the Columbia River system were about 203 million juveniles and 

 natural production was about 145 million juveniles. The 348 million juveniles are about 30 

 percent more than estimated historical production. 



Seals and sea lions are significant potential competitors as well as predators of salmonids in 

 marine waters. Estimated annual consumpfion of Pacific herring in Oregon and Washington 

 waters by seals and sea lions is almost 35 million pounds. If these herring had been consumed 

 by salmon they could have produced almost 4 million pounds of salmon flesh. The increase in 

 seals and sea lions in nearshore waters could be a significant competitive interaction in years of 

 poor biological production, such as the early 1980s and 1990s. 



Another potential competitor for food for juvenile salmonids is the American shad. The 

 Columbia River adult shad population has increased to 4 million in 1990 and billions of juvenile 

 shad could be produced annually. Shad feed on zooplankton and insect larvae, and dietary 

 overlap with juvenile salmonids in the Columbia River is significant. There is inference for food 

 competition between shad and juvenile salmonids in the Columbia Estuary. 



