not exceed 75° F. in sections where brook trout commonly occur 

 and apparently thrive. 



The limiting temperatures are higher in the case of brown and 

 steelhead trout. Temperatures as high as 83° F., for the former, 

 and 85° F., for the latter were recorded. 



The spring and summer of 1921 has been a particularly good 

 one in which to test out various temperatures on trout, because of 

 the unusually prolonged warm weather in May, June and early July. 

 The water temperatures ranged from four to six degrees higher than 

 normal during this period. 



Early in May, some brook, brown, and steelhead trout were 

 placed in wood races 4 feet wide by 20 feet long, supplied with 

 creek water whose temperature was known to be high in summer. 

 Everything progressed smoothly until June 27 when at a tempera- 

 ture of 83.3° F., the brook trout became greatly distressed and re- 

 fused to eat. The table which follows records the daily water tem- 

 peratures and the progress of events from this date until the end 

 of the test. 



Effect of Variation in Temperature on Brook, Brown, and Steelhead 



Trout 



Date. 



1921 



June 27 



28 



29 



30 



July 1 



2 



3 



4 

 5 

 6 



Effects 



Brook trout distressed. 



Brooli trout recovered and feeding. 



Apparently normal. 



Apparently normal. 



Apparently normal. 



Apparently normal. 



Brook trout 20 per cent dead. Steel- 

 heads and Browns distressed. 



Brook trout 50 per cent dead. 



Brook trout all dead. 



Brown trout .50 per cent dead. Steel- 

 head trout 20 per cent deal. All 

 others distressed. 



All trout dead. 



The brook trout passed through a temperature of 83.3° F. with- 

 out loss, but with evident distress and failure of appetite. They ap- 

 parently recovered on a drop of nine degrees over night and a maxi- 

 mum of 79.7° the following day. They lived through five suc- 

 ceeding days with the maximal temperatures ranging from 78.8° 

 to 80.7° F., but began to die at 84.2° (mortality 20 per cent). None 

 died the following day, July 4, at 82.4° ; but on July 5 at a tem- 

 perature of 83.2° F., the mortality was 100 per cent. 



60 



