1932 ANNUAL REPORT. 1Q31 55 



taken in 250 c.c. glass-stoppered bottles, and immediately packed in ice for 

 laboratory analysis. Analyses were made for oxygen, normal carbonates and 

 hydroxides, bicarbonates, etc. For methods see the thirty-eighth annual report, 

 Provincial Board of Health, Ontario, 1919. 



Experiments were divided into two series known as Series I and Series II. 

 Each experiment was conducted in duplicate to reduce accidental errors and 

 to provide a check on the results obtained. Duplicates were lettered "A" and 

 "B." Cage "A" was located east of cage "B." 



Careful precautions were taken in lowering and raising the fish in the water. 

 The temperature of the water from the bottom to the eight-metre level was 

 recorded at four-metre intervals and at two-metre intervals from the eight- 

 metre level to the surface. The rate of lowering and raising was adjusted so 

 that the fish did not experience a temperature change more rapid than one 

 centigrade degree per minute. Raising and lowering was not done continuously, 

 several rest periods being allowed to enable the fish to adjust themselves to 

 the new pressures. The cages were lowered and raised by means of a windlass 

 with an eight to one ratio. 



Counts to determine the distribution of copepods were made. The con- 

 centrated plankton haul was gently but thoroughly agitated and a 5 c.c. sample 

 was removed. The copepods in this sample were counted under a binocular 

 microscope and the total number in the haul was then calculated. The sample 

 was then returned to the bottle which was sent to the Department for 

 confirmation. 



Enough fish stomachs were analysed to give the writer an idea of what 

 was being eaten at each location. The remainder were sent to the Department 

 for analysis. 



To understand the lake conditions one must consider the normal and 

 unusual movements of the water. Under the influence of westerly winds, there 

 is usually a marked west to east drift along the shore. This is characterized 

 by clear, cold water with a definite thermocline. It bears an abundant copepod 

 fauna whose region of maximum density is usually about eight metres below 

 the surface. This region rises or lowers with changing conditions; light and 

 temperature being the two most apparent factors. 



Occasionally in the early summer and more often in the late summer, 

 easterly winds set up an unusual east to west drift of water along the shore. 

 As a rule such a drift lasts from a few days to a week but this year an east to 

 west drift began on August 2nd and continued without interruption until August 

 16th. On August 16th strong westerly winds reversed it, but it changed back 

 again on August 19th and flowed east to west without interruption until the 

 time of writing (August 26th). 



This drift brought large quantities of warm water toward the shore. The 

 thermocline gradually lowered and then disappeared. By August 13th the 

 water, at 16 metres depth, one mile from shore, had reached a temperature of 

 20.6 degrees C. at the bottom and 20.7 degrees C. at the top. The warm water 

 first lowered the region of maximum copepod density and later reduced the 

 copepod population to less than 20 per cent, of what it had been under normal 

 conditions. The return to a normal drift on August 16th was followed by a 

 marked increase in the copepod population. During the east to west drift 

 the water was more turbid than usual. 



The bottom of the lake slopes downward at the rate of about 16 metres 

 per mile. Close to the shore it is composed of sand and silt and a certain amount 

 of debris. Opposite the headlands there are many stones ranging in size up 



