A survey was conducted in 1997-1998 to identify the distribution of non-native signal crayfish (Pacifastacus leniusculus) and larval California giant salamanders (Dicamptodon ensatus) within the upper Redwood Creek watershed (Marin County, California). The crayfish is widely distributed along the mainstem Redwood Creek. It was found in lower Fern Creek but not in any first order tributaries or above fish barriers. While present throughout the study area, larval California giant salamanders were found mainly in small headwater tributaries. Larval salamanders appear to use habitats in accordance to their availability, while signal crayfish were rarely found in shallow water habitats and appeared to prefer scour pools. Evidence of predation by signal crayfish on larval giant salamanders was found under confined conditions. Controlled laboratory and field experiments would be needed to determine whether competitive exclusion is occurring. Because of its widespread occurrence in the headwater streams surveyed in this project, California giant salamanders would be an appropriate indicator species for those interested in monitoring the health of small headwater streams. Future long-term monitoring using California giant salamanders should be based on permanent monitoring reaches with periodic basinwide habitat and animal surveys to determine if reaches are representative of basinwide conditions.
