134 



PROBLEMS OF LAKE BIOLOGY 





f^resencQ of perc/i m /oJcg trout stomochs 



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Moy 



J'une 



(J'u/y 



A u 



ai 



Sept. 



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Thmperoturos of the upper c*0 /nefres of looter 



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/4-/7 



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Fig. 1. Amounts of perch foinid in lake trout stomachs in 1937 and 1938, Lake Opeongo, Algonquin 

 Park, Ontario. The absolute values in the two years are not directly comparable. The Aveights given 

 for 1937 are calculated from the lengths of the perch ingested, whereas the weights for 1938 are the 

 actual weights of the stomach contents. The calculated -weights are at least twice the actual weight of 

 perch present in the stomachs, and the graph has been adjusted by plotting the values for 1937 on half 



the scale used to plot the values for 1938. 



of food as take them through barriers set limnion of Lake Meiidota to feed, although 



up by thermal stratification, there are some they would soon die if they remained there, 



exceptions. Pearse and Achtenberg (1920) Similarly Juday and AVagner (1908) found 



found that perch invade the stagnant hypo- that lake trout commonly entered waters in 



