Responses of Fish to the 1980 Eruption of Mount St. Helens

Fish are important components of the Mount St. Helens aquatic system. Historically, no other region of Washington State supported as many native freshwater and anadromous species (anadromous fish mature in the ocean but spawn in freshwater) as did the region near Mount St. Helens (Table 12.1; McPhail 1967; McPhail and Lindsey 1986). Many of the anadromous species, including Pacific salmon (Oncorhynchus spp.) and eulachon (Thaleichthys pacificus), are keystone species that provide an important trophic link between aquatic and terrestrial ecological systems and are the foci of food webs that depend on marine-derived nutrients (Willson and Halupka 1995; Bilby et al. 1996; Levy 1997; Cederholm et al. 2001). In addition, fish are important consumers within rivers and lakes and can influence the species composition and structure of biological communities of these aquatic systems through herbivory, predation, and competition (Power 1990).