Effects of Mount St. Helens Eruption on Salmon Populations and Habitat in the Toutle River

摘要

The eruption of Mount St. Helens on May 18, 1980 caused massive devastation of the fishery resources in the Toutle River watershed. Catastrophic changes caused by the debris avalanche, pyroclastic flows and mudflows destroyed fish populations and 218 km (77 percent) of the 280 km of anadromous fish habitat formerly utilized by salmonids. Adult salmon spawned in unstable volcanic substrates with average concentrations of fine particles ranging from 11.2 percent to 36.0 percent in 1981 and from 11.2 percent to 33.5 percent in 1982. Survival of eggs to hatching stage in volcanic substrate ranged from 50 percent to 95 percent. Any success was attributed to groundwater upwelling. Juvenile coho mortality ranged from 0 percent to 83 percent during the summer period and was closely associated with high water temperature. Mortality during winter ranged from 62-83 percent in unaffected streams and 82-100 percent in affected streams and was associated with channel stability, suspended sediment, and the amount of cover provided by large organic debris.