Abstract
Throughout the world, historically large populations of native anadromous salmonids are in severe decline or extinct. In the United States alone, twenty-six Evolutionarily Significant Units of Pacific salmonid are currently threatened or endangered. These declines are most commonly attributed to degradation of spawning and rearing habitat resulting from increased loading of fine sediments. Although excessive loading of fine sediments into rivers is well known to degrade salmonid spawning habitat, its effects on the demographically critical rearing juveniles have been unclear. We experimentally manipulated fine bed sediment in a northern California river and examined responses of a juvenile salmonid. Increasing concentrations of deposited fine sediment decreased growth and survival of juvenile steelhead trout. These declines resulted from a shift in invertebrates toward burrowing taxa unavailable as prey and from increased steelhead activity and injury at higher levels of fine sediment. The relationship between deposited fine sediment and juvenile steelhead growth is linear. This suggests that there is no threshold below which exacerbation of fine sediment delivery and storage in gravel bedded rivers will be harmless, but also that any reduction will produce immediate benefits for salmonid restoration.
Mary Power