99 



A calcium ion concentration of 2.99 me/1 was measured in a euphotic 

 zone water sample during the fall overturn, 1972. According to Reid's 

 (1961) classification for biological productivity, a calcium ion concen- 

 tration greater than 1.25 me/1 is considered "rich". Clark Canyon con- 

 tains over twice this amount and must be considered a fertile environ- 

 ment. 



From December, 1971 to November, 1972, thirty-one algal genera (6 

 classes) were observed in the euphotic zone of Clark Canyon Reservoir. 

 In order of decreasing abundance, the five genera with the largest mean 

 annual standing crops were: Asterionella , Aphanizomenon , Cryptomonas , 

 Rhodomonas , and Synedra . The seasonal abundance of these genera are 

 compared in Figure 3. A blue-green algae bloom, composed primarily of 

 Aphanizomenon sp. , peaked in September, 1972. Water temperature was the 

 only variable measured that was significantly correlated with phytoplank- 

 ton standing crops. 



Five major zooplankton taxon were encountered during the study. 

 Daphnia schodleri and Cyclops bicuspidatus thomasii were the dominant 

 zooplankters during all seasons. D. schodleri became the first abundant 

 zooplankter, appearing in large numbers in mid-May. Water temperatures 

 and chlorophyll a_ concentrations were the only measured variables signif- 

 icantly correlated with populations of JL schodleri . 



METHODS 

 Fish were sampled in Clark Canyon Reservoir using gill nets, trap nets, 

 and seine nets. The gill nets used were 125-foot x 6 foot experimental nets 



