Gill nets used were 125 feet long, six feet deep, with mesh sizes of ¾ inch to 2½ inches. Nets, weighted to sink, were placed at right angles to the current and attached at the banks with rope.
Sodium Cyanide
Pellets of sodium cyanide were used infrequently to collect fish from a moderately fast riffle over gravel bottom that was overgrown with willows, making seining impossible. The pellets were dissolved in a small amount of water, a seine was held in place, and the cyanide solution was introduced into the water a short distance upstream from the seine, causing incapacitated fish to drift into the seine. Most of these fish that were placed in uncontaminated water revived.
Rotenone
Rotenone was used in a few small pools in efforts to capture complete populations. This method was used to check the validity of other methods, and to reduce the possibility that rare species would go undetected. Rotenone was applied by hand, and applications were occasionally supplemented by placing rotenone in a container that was punctured with a small hole and suspended over the water at the head of a riffle draining into the area being poisoned. This maintained a toxic concentration in the pool for sufficient time to obtain the desired kill. Rotenone acts more slowly than cyanide, allowing more of the distressed fish to rise to the surface.
Dyes
Bismark Brown Y was used primarily at the upper Neosho station to stain large numbers of small fish. The dye was used at a dilution of 1:20,000. Fishes were placed in the dye-solution for three hours, then transferred to a live-box in midstream for variable periods (ten minutes to twelve hours) before release.
Determination of Abundance
In the accounts of species that follow, the relative terms "abundant," "common," and "rare" are used. Assignment of one of these terms to each species was based on analysis of data that are presented in Tables 9-16, (pages 402, 403, 404, 405, 408, 410, 411, 414-415, and 416). The number of fish caught per unit of effort with the shocker (Table 10) and with seines (Table 11) constitute the main basis for statements about the abundance of each species at all stations except the upper Neosho station. Species listed in each Table (10 and 11) are those that were taken consistently by the method specified in the caption of the table; erratically, but in large numbers at least once, by that method; and those taken by the method specified but not the other method.
For the species listed in Table 10, the following usually applies: abundant=more than three fish caught per hour; common=one to three fish caught per hour; rare=less than one fish caught per hour.