Using seabird associations with the Columbia River Plume to demonstrate the conservation importance of river plumes

Abstract

**Abstract:** The Columbia River on the west coast of the United States is the 21st largest river in the world in terms of annual mean flow. Freshwater discharge from the Columbia River flows into the northern California Current Ecosystem, one of the most productive marine food webs in the world. A large, dynamic plume is formed at the mouth of the river, which has a strong regional influence on nearshore oceanography and productivity. Using at-sea surveys, land-based surveys, and satellite telemetry, we demonstrated that the plume also strongly affects the distribution, abundance, and habitat preferences of seabirds and seabird prey. Specifically, we found that two numerically dominant piscivorous seabirds, common murres (Uria aalge) and sooty shearwaters (Ardenna grisea), aggregate in large numbers in this region, preferentially select plume habitat, and respond to spatial and temporal changes in plume dynamics. Coastal pelagic fishes consumed by seabirds such as northern anchovy (Engraulis mordax) are disproportionately more abundant in plume waters compared to adjacent waters, suggesting that foraging birds use the plume to increase prey encounter probabilities. Plume effects are evident in both summer and winter, although the dynamics driving winter use of the plume are not well-understood. Given predicted changes in freshwater runoff with climate change, and high levels of human use of the Columbia River and other large rivers for commercial and recreational activities, we suggest that river plumes are under-appreciated regions of global conservation importance for seabirds. **Authors:** Jeannette Zamon¹, Elizabeth Phillips², Josh Adams³ ¹NOAA Fisheries - Pt. Adams Research Station, ²NOAA Fisheries - Northwest Fisheries Science Center, ³US Geological Survey