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The Effects of Pool Size and Beaver Activity on Distribution and Abundance of Warm-water Fishes in a North Missouri Stream

Willis D. Hanson and Robert S. Campbell
The American Midland Naturalist
Vol. 69, No. 1 (Jan., 1963), pp. 136-149
DOI: 10.2307/2422849
Stable URL: http://www.jstor.org/stable/2422849
Page Count: 14
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The Effects of Pool Size and Beaver Activity on Distribution and Abundance of Warm-water Fishes in a North Missouri Stream
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Abstract

The linear distribution of fishes appeared to be related to stream gradient and area of the watershed; headwater species occurred where the gradient was 8.2 feet per mile, and the watershed area was less than 93 square miles. The influence of large deep pools on species distribution is possibly more significant than, and superimposed on, this basic pattern. The presence of beaver pools in the headwater section affected fish habitat through (1) a greatly increased volume of water; (2) providing deep pools in times of intermittent stream flow; (3) increasing variety of fish habitat. The effect of beaver pools on the fish population was seen in (1) an increased variety and abundance of species; (2) a greatly increased standing crop. The standing crop of plankton in beaver pools was approximately five times as great as in the stream proper. Whereas land use and stream straightening frequently have deleterious effects on fish populations because of silt deposition and shallowing of pools, beaver activity appeared to improve the carrying capacity of the stream for warm-water fishes.

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