Excerpted with permission from Salmon's falling fortunes
By Lance Robertson©THE REGISTER-GUARD
Sunday, April 13, 1997
A variety of human activities hurts salmon and their habitat
Logging: Erosion from clear-cut logging and road building, especially on steep, unstable hillsides, has muddied streams and rivers where salmon spawn. Removing trees along streams warms water. Cutting big trees also robs streams of large logs that used to fall into the water, creating pools for salmon to rest, feed or spawn.
Farming, ranching: Overgrazing of cattle and other livestock has stripped stream banks of vegetation increasing water temperatures and causing silt that can choke salmon eggs. Livestock waste pollutes water. Unscreened irrigation canals can trip young salmon as they migrate to the ocean. Fertilizers can decrease water quality.
Urban development: Population growth has increased pollution of streams with sewage, industrial waste, oil and gas from street runoff and fertilizers from lawns and gardens. Development also can destroy streamside habitat.
Weather: Climate change, such as the El None ocean-warming phenomenon or global warming, prevents the upwelling of colder nutrient-rich water, robbing salmon of food. Salmon populations drop during El Nino years.
Overfishing: As many as 1.6 million coho migrated up West Coast streams annually at the turn of the century. For decades, coho were the lifeblood of a commercial and sport fishery worth $100 million or more in yearly revenues.
Hatcheries: State and federal fish agencies launched major hatchery programs in the 1960s to counter the decline of wild salmon. But hatcheries now are blamed for the wild stocks' decline. Fishing limits were high, resulting in a high take of wild fish. Hatcheries also dilute the wild fish gene pool.
Predators: Coho face a gauntlet of predators on their way to the ocean. Seals and sea lions wait in estuaries for young salmon and again when they return two years later. In the ocean, salmon can be eaten by killer whales and porpoises.
Dams: A few coho streams in Oregon and Northern California have dams and hydroelectric power turbines that can be deadly to salmon. Slack water behind dams can slow or confuse salmon.