Session A7- Research

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Nislow, Keith; Letcher, Benjamin; Hudy, Mark; Smith, Eric
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Improperly designed road crossings act as barriers to movement of aquatic organisms and can depress local abundance and reduce local species richness, with potential impacts on population viability and biotic diversity. However, because abundance and richness are highly spatially and temporally heterogeneous and the relative importance of immigration on demography is uncertain, population and community-level effects can be difficult to detect. In this study we tested the effects of barriers to upstream movements on the local abundance and species richness of a diverse assemblage of resident stream fishes in the Monongahela National Forest, West Virginia, USA. Fishes were sampled using simple standard techniques above- and below- road crossings that were either likely or unlikely to be barriers to upstream fish movements (based on physical dimensions of the crossing). We predicted that abundance of resident fishes would be lower in the upstream sections of streams with predicted impassable barriers, that the strength of the effect would vary among species, and that these variable effects on abundance would translate into lower species richness. Supporting these predictions, stream sections located above predicted impassable culverts had fewer than half the number of species and less than half the total fish abundance, while stream sections above and below passable culverts had essentially equivalent richness and abundance. Our results are consistent with the importance of immigration and population connectivity to local abundance and species richness of stream fishes. In tum, these results suggest that when measured at appropriate scales (multiple streams within watersheds), with simple protocols amenable to use by management agencies, differences in local abundance and species richness may serve as indicators of the extent to which road crossings are barriers to fish movement, and help determine whether road crossing improvements have restored connectivity to stream fish populations and communities.