Echosounding revealed that large numbers of fish continually inhabit the midwater zone of 45,440-acre Bull Shoals Reservoir. Fish population sampling in these waters with conventional gear had proved relatively inefficient. In an attempt to develop a method for sampling these waters, a modified and scaled-down version of the “British Columbia” midwater trawl was constructed and operated. Night trawling produced catches composed principally of threadfin shad, Dorosoma petenense (Günther). Fish were found to be vertically stratified in a sharply limited layer between the surface and the thermocline. Concentration was found to decrease with increasing depth but the horizontal distribution was remarkably uniform. The development of a technique for deriving an order of magnitude population estimate is presented. The method employs catch per unit of effort data, the volume of water sampled in a standard haul, depth of strata sampled and volume of water in each stratum. From 72 vertically stratified hauls taken with an 8-foot midwater trawl in the late summer of 1965, a population estimate of 400.8 × 106 young-of-the-year threadfin shad in the reservoir was calculated.
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Houser et al. (1967) studied this question.