Influence of Differential Angling Mortality and Stream Gradient on Fish Abundance in a Trout-Sculpin Biotope

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Abstract
The lowest 2.4 miles of a small, unfished tributary of the St. Joe River was treated with rotenone in July 1964. Four species of fish, Salmo clarki (369 fish), Salvelinus fontinalis (2,361 fish), Cottus confusus (3,513 fish) and Cottus rhotheus (161 fish), formed the total population. The relative and absolute numbers and weights of S. clarki increased upstream whereas those of S. fontinalis increased downstream. In contrast, C. confusus was about evenly distributed and C. rhotheus was present in just the downstream 0.3 mile. With few irregularities, the mean lengths of the three most abundant species increased in an upstream direction. The total biomass of fish was 50 lb per acre of which 83% were trout and 17% were sculpins. S. clarki and S. fontinalis, 6 inches or longer, accounted for 75% and 55% of their species weight, respectively. In this length class, a 32 man‐hour fishing effort prior to rotenone treatment resulted in the capture of 50% of the cutthroat and 25% of the brook trout.

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