Kerotello canodensis Kerotello cochleoris Kellicottio longispino Ploesomo hudsoni Conochilus unicornus 



Asplonchno priodonto Epischuro nevodensis Bosmino coregoni Cerolium hirundinello Combined 



PER C E NT 



Figure 4. --Vertical distribution of zooplankton by species in Bare Lake, 1957, as a per- 

 centage at depth of the accumulated counts. 



lake on an organism per liter basis. Also, 

 in any comparison, the method of capture must 

 be considered. A third consideration, rarely 

 mentioned in plankton papers, is the presence 

 and abundance of plankton predators such as 

 populations of Chaoboms and fish. Edmondson 

 wrote (1957, p. 239-240): "Although many 

 animals are known to prey on zooplankton, 

 little is known of the rate of predation or the 

 effect on the zooplankton population." 



As indicated in figure 6, Bare Lake apparently 

 had about three times as many zooplankters 

 per liter of water in the summer of 1957 as in 

 the summer of 1952. The question arises as to 

 why this was so. Did Bare Lake actually pro- 

 duce more zooplankton in 1957, or, perhaps 

 because of a possible longer life expectancy, 

 were zooplankton merely available for capture 

 by the net over a longer period of time? 

 Perhaps in 1952, the population was subjected 

 to more intense grazing by predators than in 

 1957. Certainly the 1952 zooplankton had the 

 advantage of inhabiting an environment en- 

 hanced by the addition of fertilizers. Bare 



Lake was then in its third summer of artificial 

 fertilization with di-ammonium phosphate and 

 sodium nitrate. The application of these ferti- 

 lizers to the lake was discontinued after 1956. 

 Unfortunately the exact abundance of each fish 

 species inhabiting the lake is not known. Data 

 are available however in unpublished records 

 of the Fish and Wildlife Service that indicate 

 relative abundance for all species present 

 (table 2). 



Essentially Salmo gairdneri, Oncorhynchus 

 tshawytscha, and Coitus aleuticus are too few 

 in number to affect seriously the zooplankton 

 population and may be ignored. 0. nerka ap- 

 pears to have been slightly (12 percent) more 

 abundant in 1952 than in 1957. However, 

 Salvelinus malma and 0. kisutch appear to have 

 been definitely on the increase throughout the 

 study period (table 2). S. malma was quite 

 likely twice as abundant in 1957 as in 1952. 

 Although Gasterosteus aculealus was known to 

 be abundant there are no accurate estimates 

 of numbers in the records, and it may be as- 

 sumed that its abundance was unchanged over 



8 



