Occupancy patterns of mammals and lentic amphibians in the Elwha River riparian zone before dam removal

The downstream transport of sediments and organics and upstream migration of anadromous fishes are key ecological processes in unregulated riverine ecosystems of the North Pacific coast, but their influence on wildlife habitats and populations is poorly documented. Removal of two large hydroelectric dams in Washington’s Elwha Valley provides an unprecedented opportunity to study long-term responses of wildlife populations to dam removal and restoration of these key ecological processes. We compared pre-dam removal patterns in the relative abundance and occupancy of mesocarnivores, small mammals and lentic amphibians of the Elwha River riparian zone above, between and below the dams. Occupancy of riparian habitats by three mesocarnivore species diminished upriver but did not appear to be closely linked with the absence of salmon in the upper river. Although the importance of salmon in the lower river cannot be discounted, other gradients in food resources also likely contributed to observed distribution patterns of mesocarnivores. Abundance and occupancy patterns within congeneric pairs of new world mice (Peromyscus spp.) and shrews (Sorex spp.) indicated that closely related species were negatively associated with each other and responded to habitat gradients in the riparian zone. The availability of lentic habitats of amphibians was highly variable, and occupancy was low as a result of rapidly changing flows during the larval development period. We speculate that long-term changes in habitat conditions and salmon availability following dam removal will elicit long-term changes in distribution of mesocarnivores, small mammals and amphibians. Long-term monitoring will enhance understanding of the role of fish and restored ecosystem processes on wildlife communities along salmon-bearing rivers in the region.