150 Theories and Techniques of Management 



dissolved oxygen and forced the fish to gulp air at the surface. Fish re- 

 covered fully when placed in fresh water if they were collected when 

 still gulping air. This method is practical only in small ponds because of 

 the cost of the sulfite ( 10 cents per pound ) .^^^ 



FISH POPULATION ADJUSTMENT 



As mentioned above, there are a number of ways that a low-producing 

 population may be adjusted to achieve a higher yield without eliminating 

 and replacing the entire population. These methods are applicable when: 



(1) A population consists of desii-able fishes, but with some species stunted 

 and others becoming scarce due to excessive competition. 



(2) There is high demand for one or two species and low demand for one 

 or more other species inhabiting the same water. 



(3) Eliminating the indigenous population and starting over with a new one 

 is impossible or impractical. 



Use of Nets and Seines 



In small ponds, wire traps or wing nets are used to reduce excessive 

 populations of crappies, bluegills, and other sunfishes and to permit an 

 increase in the largemouth bass. Wing nets employed in Fork Lake con- 

 trolled bluegills and allowed the development of a very large bass popula- 

 tion. The very same type of selective cropping may be done with intensive 

 seining provided the pond or lake basin lends itself to the making of a 

 productive seine haul, and the seine and crew are available. ^^^ The main 

 drawback to either of these methods is that they both entail a great deal 

 of work, and some rather expensive equipment. Also, relatively few lakes 

 or ponds are well adapted to cropping with wing nets or seines, and the 

 average pond or lake owner does not have access to this equipment. 



Partial Poisoning 



Soon after the use of rotenone to poison an entire population became 

 widespread fisheries biologists noted its differential toxicity to various 

 species and sizes of fishes. This led to the development of the selective 

 or partial poisoning technique with rotenone, designed to kill certain parts 

 of a population without seriously damaging the remainder of it. This 

 technique for removing warm-water fishes from trout lakes has been 

 described on page 143. 



In 1945 and 1946, I applied a shoreline treatment of rotenone to Park 

 Pond of the South Pollywog Association holdings of a stripmine pond area 

 in east central Illinois, in order to reduce an excessive population of 

 gizzard shad and small sunfish. Later, when Dr. R. Weldon Larimore was 



