152 Theories and Techniques of Management 



the production of new bluegills or growth o£ those escaping poisoning. 

 Much of this space would still be available when the bass spawned the 

 following spring, insuring improved survival of young bass. In the in- 

 stances cited above, timing is of utmost importance if the desired results 

 are to be forthcoming. 



The greatest weakness of the partial poisoning technique is that with- 

 out supplementary information on the standing crop of fish, it is im- 

 possible to gauge accurately the extent of the operation in terms of the 

 per cent of a fish population removed.^^ Usually the operation is too con- 

 servative for optimum results, and a repetition may be necessary. In some 

 instances it is useful and practical to do a partial poisoning operation just 

 prior to the spawning season each year for as long as 5 successive years. 

 Each treatment insures the production and survival of a year class of bass 

 for that year and before the end of 5 years the bass population should be 

 approaching the maximum that the water will support. 



Swingle, Prather, and Lawrence ^^^ recommend the stocking of 150 to 

 200 fingerling bass per acre following a summer marginal poisoning 

 operation. Such a stocking might check the success of sunfish reproduction 

 which could be expected to fill up the space created by the poisoning 

 with a new year class of small bluegills, green sunfish or other kinds of 

 sunfish present. As mentioned above, this restocking is unnecessary if the 

 poisoning operation can be done in spring before the bass have spawned 

 or in the fall near the end of the fish-growing season. 



Shoreline vs. Sectional Treatment. In partial poisoning operations one 

 may poison completely a bay or an arm of a lake, using a dosage of 

 rotenone of sufficient strength to kill all fish. In such a case it may be 

 practical to separate the rest of the lake from the treated bay by blocking 

 the opening with a canvas strip, long and deep enough to reach across 

 the mouth of the bay (Figure 6.7). This strip can be hung on a wire 

 supported by posts driven into the lake bottom. 



Beckman ^ demonstrated an increase in the growth rate of rock bass 

 after he had poisoned the fish in half of a lake having a natural con- 

 striction near the center. Unless the arm or bay to be treated represents 

 one half or more of the total lake surface area, such a fish poisoning 

 operation may be insufficient to reduce a stunted fish population. 



Swingle, Prather, and Lawrence ^^^ do not favor sectional poisoning 

 because more desirable fish are killed by this method than by marginal 

 poisoning. This may or may not be a valid argument. Sectional poisoning 

 removes fishes in proportion to the relative abundance of kinds and sizes 

 in a pond or lake and, therefore, is a useful method of cropping. It is 

 probably the only technique short of complete poisoning that is effective 

 in reducing stunted populations of bullheads. 



It is often practical to combine marginal poisoning with sectional 



