History, Ecology and Restoration Potential of Salmonid Fishes in the Umpqua River, Oregon

Kelly Crispen Coates, The University of Montana

Abstract

Salmonid populations are decreasing across their historic range in the Pacific Northwest, and throughout the lower 48 states. This study incorporates a retrospective analysis of historical literature, traditional ecological knowledge as well as current ecology to determine historic salmonid abundance in the Umpqua River, Oregon and current conditions for salmonids in the context of wild salmonid restoration. Results for the Umpqua were compared to other Pacific Rim Rivers. The history of the basin and impacts to the river including settlement, agriculture, logging, mining, dam building, hatchery supplementation and non-native species introduction were reviewed. Decreases in runs were compared to impacts to the river over time to determine the impact that had the largest effect on salmonid abundance. Although anthropogenic impacts have occurred throughout the river basin, the most detrimental impact to wild salmonids was overharvest in the late 1800’s and early 1900’s. Freshwater habitat metrics were sampled to determine impacts to salmonid sustainability in the basin, and possible restoration opportunities. The metrics examined were: juvenile salmonid density, non-native fish species, water chemistry, temperature, aufwuchs, benthic invertebrates, stable isotopes of δN15 and δC13, and landscape scale attributes. All metrics were compared to those of other Pacific Rim rivers. Within the Umpqua River system, juvenile salmonid density was highest in the North Umpqua. Overall, juvenile salmonid density for the Umpqua River was comparable to pristine floodplain rivers across the Pacific Rim. Non-native species and hatchery influences have a detrimental effect on wild salmonids, and more research should investigate possible impacts. While water chemistry is not apparently limiting salmonid sustainability in the Umpqua River, water temperatures are above lethal limits in months of July and August. Marine nitrogen (δN15) signals were highest in the Main Umpqua River, and may be compounded by agriculture, however further studies are necessary to determine agricultural influence. Restoration recommendations for salmonids in the Umpqua River include a basin wide conservation and restoration plan that addresses the underlying problems of habitat fragmentation and degradation, and high water temperatures. Addressing these issues will inform restoration possibilities for related habitat concerns including the amount of available spawning habitat, available gravel for spawning and proper incubation and growing conditions for juvenile salmonids and lamprey. Given the legacy of overharvest in the basin, careful examination of the impact of increasing the limit of wild salmon and steelhead harvest to various stocks is also necessary.