166 Theories and Techniques of Management 



systematic destruction of sunfish nests. Less efiFort would be required 

 to drop a small handful of chemical salts into a nest from a boat than to 

 mechanically destroy the nest, and the former method might be more 

 eflFective. Jackson ^^ used sodium hydroxide pellets for this purpose with 

 good success. If fertilizer should prove useful in poisoning sunfish em- 

 bryos, pond fertilization would be serving a dual purpose. 



Dangers from the Use of Fertilizers. The application of inorganic ferti- 

 lizers to ponds and lakes for increasing fish production ^^^' ^^^ has not 

 been well accepted in parts of the United States outside of the southeast. 

 The objections to pond and lake fertilization are many, and it seems 

 apparent that results have been variable and quite unpredictable.^^ --' ^-' ^^ 



In the northernmost states, the suffocation of fishes under ice is com- 

 mon during severe winters with heavy snowfall. Fertilization of ponds 

 and lakes in this region increases the danger of winterkill. ^^' ^^^ Ball and 

 Tanner ^ stated that the addition of fertilizer to one of their experimental 

 ponds was the indirect cause of winterkill, because the fertilizer stim- 

 ulated the algae which later decomposed under the ice. 



In all parts of the country there is the ever-present danger of "summer- 

 kill" of fishes, where calm hot weather along with an abundance of plank- 

 ton algae may result in nocturnal oxygen depletion in lakes and ponds. ^^ 

 This occurrence is not uncommon in organically rich lakes which are not 

 fertilized. Swingle and Smith ^^^ advise against applying fertilizer when 

 rooted aquatics are decomposing. They cite an instance when an applica- 

 tion of fertilizer was broadcast over decomposing masses of Najas, with 

 the result that oxygen was depleted and bass and other fishes died. 



In Michigan ponds, the use of fertilizer could not be depended upon 

 to control higher aquatic plants,"* and produced filamentous algae even 

 if not applied until after the water had warmed in the spring.^' ^^ This 

 agreed with findings in Wisconsin ^^ and in the hard water ponds of 

 West Virginia.i^^ 



The nuisance values of algae stimulated by inorganic fertilizers are 

 stressed by several authors. Ball and Tanner^ state: "Tlie appearance of 

 the lake and its use for swimming, boating, and other recreational pur- 

 poses were adversely affected by the fertilizer. The matted green scum 

 formed by the filamentous algae around the shore and festooning the 

 marginal vegetation was very unsightly and was a hindrance to fishermen, 

 both in the use of their boats and by the fouling of their baits. The odor 

 of the decaying algae was very unpleasant." Patriarche and Ball ^^ warn 

 about the unsightly condition that occurs when a growth of filamentous 

 algae follows fertilization. Hansen, et al.,^^ describe a bloom of Rhizo- 

 chlonium sp. in Lauderdale pond (Illinois) which covered from 25 to 75 

 per cent of the surface and stopped fishing except where the alga was 

 absent. 



