Flood and Debris-flow Effects on Virginia Brook Trout Populations

Streams and rivers in the Blue Ridge Mountains of Virginia provide an excellent cold water resource and have historically supported exceptional wild trout populations. In June 1995, a flood of greater than 500-year recurrence interval created a unique opportunity to assess the impact on trout populations within 3 rivers of the Shenandoah National Park (SNP). Debris flows impacted the lower one- to two-thirds of the Rapidan, Staunton, and North Fork Moormans rivers, either extirpating or greatly depressing trout populations. The number of trout collected in debris flow areas were significantly reduced (P≤0.05) in 1996, 1997, and for the post-flood 3-year mean when compared to pre-flood means. Trout populations in the flooded headwater reaches of all 3 rivers were not reduced. Debris flows, in association with severe flooding, greatly depress and even extirpate native brook trout (Salvelinus fontinalis) populations, but flooding alone may have little effect on populations. Trout number and biomass were also greatly influenced post-flood by high numbers of young-of-the-year trout. The rapid recovery, to date, of the trout populations reflects the remarkable resiliency of native brook trout.

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