Trawls of various designs and sizes were compared to evaluate their use for monitoring and harvesting fish populations in Lake Oahe. Catches of a 10.7-m semiballoon trawl, selected to monitor changes in the fish populations from 1965 to 1970, showed a downward trend in the abundance of all species, except walleye; the decline was largest in the lower area of the reservoir with a slight increase in the upper area. Of two trawl designs tested, semiballoon trawls captured more fish per hour than high-rise trawls, and a 15.9-m semiballoon trawl with a 3.8-cm mesh cod end captured fish at the highest and most consistent rate. The size and species composition of fish caught in small-mesh trawls differed from those caught in trap nets. Trawl catches were too small to recommend or warrant their use as a commercial fishing gear, but the use of both small mesh trawls and trap nets should improve accuracy in monitoring fish populations in this reservoir.
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Federal Government Series
Evaluation of trawls for monitoring and harvesting fish populations in Lake Oahe, South Dakota