Road construction of the Redwood National Park highway bypass resulted in a large accidental infusion of fine sediments into pristine streams in Prairie Creek State Park, California, during an October 1989 storm event. This incident provided a natural experiment where we could measure, compare, and evaluate native stream amphibian densities as indicators of stream ecosystem stress. We employed a habitat-based, stratified sampling design to assess the impacts of these sediments on the densities of aquatic amphibians in five impacted streams by comparing them with densities in five adjacent, unimpacted (control) streams. Three species were sampled in numbers sufficient to be informative: tailed frogs (Ascaphus truei, larvae), Pacific giant salamanders (Dicamptodon tenebrosus, paedomorphs and larvae), and southern torrent salamanders (Rhyacotriton variegatus, adults and larvae). Densities of amphibians were significantly lower in the streams impacted by sediment. While sediment effects were species specific, reflecting differential use of stream microhabitats, the shared vulnerability of these species to infusions of fine sediments is probably the result of their common reliance on interstitial spaces in the streambed matrix for critical life requisites, such as cover and foraging. Many streamdwelling amphibians are highly philopatric and long-lived, and they exist in relatively stable populations. These attributes make them more tractable and reliable indicators of potential biotic diversity in stream ecosystems than anadromous fish or macroinvertebrates, and their relative abundance can be a useful indicator of stream condition.
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