Fire and bull trout: spawning patterns in rock creek and western Montana

Abstract

Bull trout (Salvelinus confluentus) is a native salmonid species that is listed as threatened under the U.S. Endangered Species Act. Bull trout are a species that seems particularly sensitive to changes in water conditions, requiring cold, clean, and connected habitat. Although information for bull trout habitat requirements exists, the cause for many population declines remains unknown. Therefore, the main objective of my study is to examine the influence that large wildfires >3.64 square kilometers have on bull trout using tributaries for spawning. The influence wildfires have on bull trout was determined by comparing the number of spawning nests called redds annually before and after a fire. I also compared sediment data before and after a fire when available. After the fire, mean redd counts decreased each year in seven of the nine tributaries with available data, except for the North Fork of the Blackfoot River and Skalkaho Creek Sediment data did not align with the fire history data but showed periodic spikes in sediment that exceeded bull trout physiological tolerance. My study shows the decline of bull trout throughout much of Western Montana and should indicate the importance of restoration in conservation priorities.