Management Techniques 143 



dicated that a concentration of 0.5 ppm of derris powder with 5 per cent 

 rotenone content should be lethal to all kinds of fishes. Also, a 14-degree 

 elevation of water temperature from 60°F to 74°F decreased the reaction 

 time to equilibrium loss and death of the fish by one-half, and rotenone 

 was found to be somewhat more toxic in acid than in alkaline water. 



Biologists soon discovered that derris and cube mixtures with water 

 were slow in penetrating the deeper waters of thermally stratified lakes. 

 For this reason it was physically possible to kill warm-water fishes such as 

 yellow perch, rock bass, and largemouth bass inhabiting the upper warmer 

 layers of water without killing many brook or rainbow trout,-^- 07, iii jj^_ 

 habiting the colder strata below (Figure 6.4). Hayes and Livingstone^"^ 

 combined the technique with the stocking of brook trout in a Nova Scotia 

 lake and were able to increase the trout yield by 230 per cent. 



Wide experience with rotenone-bearing compounds including the newer 

 emulsions formulated by several chemical manufacturing companies has 

 shown that it is risky to depend upon a dosage of material containing 

 5 per cent rotenone of less than 1 ppm to give a complete kill of fish.^^ In 

 Illinois we have used a standard dosage of 3 pounds of 5 per cent 

 rotenone-bearing material or 3 pints of emulsifiable rotenone, 5 per cent, 

 per acre-foot of water, a dosage somewhat larger than 1 ppm. The extra 

 chemical takes care of: (1) inaccuracies of lake volume estimates, (2) 

 fishes showing high resistance to rotenone, ( 3 ) water of high organic con- 

 tent and/or alkalinity, and (4) unevenness of spreading. It is better to 

 use too much rotenone than too little when all of the population must be 

 killed (Figure 6.5) because if a few fish survive, both the cost of the 

 rotenone and the treatment time of the crew have been lost, and the 

 lake must be retreated. 



In every case special methods of application should be used to carry 

 the rotenone into deeper parts of a lake. One of the simplest is to in- 

 troduce the rotenone mixture or emulsion dirough a weighted hose con- 

 nected to a tank supported in the boat a foot or two above the water 

 level. The movement of the boat ( driven by an outboard motor ) and the 

 action of gravity forces the liquid into the deeper waters. The surface 

 and edges of the pond or lake can be treated by the use of any type of 

 small-power sprayer apparatus, and this same equipment can be used to 

 pump the liquid into deep water. A hand sprayer is sometimes eflFective 

 for covering edges of a small pond; for treating open surface water, the 

 material can be poured over the side of the boat in advance of an out- 

 board motor. Bilge-pump attachments available widi some makes of 

 outboard motors have been used for spreading emulsifiable rotenone. 

 Powdered derris or cube suspended in water might clog a bilge-pump 

 attachment. 



Care must be exercised to spread the fish-killing material as evenly 



