Salmonid Spawning Habitat in Rivers: Physical Controls, Biological Responses, and Approaches to Remediation
Salmon Bioturbation and Stream Process
Allen S. Gottesfeld, Marwan A. Hassan, and Jon F. Tunnicliffe
A considerable body of research has been built in the past 50 years in order to understand salmon habitat and the influence of anthropogenic activities. Geomorphologists have played an important role in this research, having described the sedimentary conditions, and channel morphology requirements for productive salmonid populations (Bjornn and Reiser 1991; Kondolf and Wolman 1993; Montgomery et al. 1999). Much of this work has sought to understand the sediment generated from catchment disturbances such as logging and associated activities such as road construction on salmonids, their habitat, and their reproductive dynamics. Recent research has considered the role of salmon as geomorphic agents controlling their own habitat (Montgomery et al. 1996; Gottesfeld 1998; Gottesfeld et al. 2004). Far fewer investigations have attempted to quantitatively describe the effects of salmon as geomorphic agents and their role in mobilizing sediment.
In the course of excavating their spawning redds, riverine salmonids modify the streambed morphology and move sediment downstream. What is most remarkable about the excavation by the fish is that the individual actions of high concentrations of spawners lead to sediment mobilization and to large-scale changes in the local bed topography and channel morphology. In streams with dense populations of salmon, the whole surface of spawning reaches may be modified (Montgomery et al. 1996; Peterson and Quinn 1996; Gottesfeld et al. 2004). At these sites, salmon bioturbation may be the dominant or subdominant agent of sediment transport and affect the composition, stratification, and fabric of the stream bed sediments (Kondolf et al. 1993; Montgomery et al. 1996; Gottesfeld et al. 2004). Since some populations of salmon home to the stream and sometimes to the reach in which they were hatched (Wagner 1969; Cramer 1981), they may have a profound cumulative effect over many years.