344 



BULLETIN OF THE BUREAU OF FISHERIES 



Drummond (1890) published a series of temperatures taken in Georgian Bay 

 on July 27, 1888, which indicates that the thermocline for the bay was around 10 

 fathoms. A few temperature readings that I took in Lake Huron in September of the 

 years 1917 and 1919 (see Table 12) indicate that the thermocline was somewhere 

 between 15 and 35 fathoms, but probably a great deal higher than 35 fathoms, as 

 Drummond's records indicate for Georgian Bay. Figures given in the same table 

 show that the thermocline in Lake Nipigon in late July, 1922, was around 12 fathoms 

 and in Lake Michigan in August, 1920, above 24 fathoms. Records for Lake 

 Superior (in Table 13) indicate that on August 5 and 10, 1922, it was around 5 

 fathoms, except in Black Bay, where, on July 20, there was no evidence of a thermo- 

 cline at 8 fathoms. Figures given by Coleman (1922) show that in Lake Ontario, 

 on October 3, 1922, the thermocline was around 20 fathoms. 



In Lake Nipigon, on July 28, 1922, there was no evidence of warming at 56 

 fathoms. The studies of Clemens, however, show that winds may lower the ther- 

 mocline considerably and the bottom waters may be warmed slightly even to greater 

 depths. In Lake Michigan the deepest temperatures recorded in August and October, 

 1920, at 40 and 49 fathoms, respectively, showed a fraction of a degree above the 

 temperature of maximum density; and in August, 1894, Ward (1896) found about 

 the same temperature there down to 72 fathoms. In Lake Huron the temperature of 

 maximum density was reached on September 12, 1917, at 65 fathoms and on Septem- 

 ber 18, 1919, at 60 fathoms. In Lake Superior, the temperature of 4° was obtained 

 on August 24, 1921, at 54 fathoms and on June 14, 1922, at 25 fathoms. Coleman's 

 (1922) figures for Lake Ontario show no warming at 50 fathoms on October 3, 1922. 

 It may be noted that bottom temperatures of 4° in depths of more than 50 fathoms 

 also have been recorded in summer from Cayuga and Seneca Lakes in New York. 



These data indicate that during the warmest part of the year there is little 

 mixing of water by wind action in any of the lakes below 20 fathoms, and at depths of 

 40 fathoms currents had not brought about the admixture of warmer surface water 

 and bottom water in volume sufficient to raise the bottom temperature more than a 

 fraction of a degree above 4° C, the lowest temperature that could occur on the 

 bottom in summer. Of course, temperature penetration depends largely on the 

 amount of wind action, and the more continued and violent the winds in summer, 

 the deeper would be their effects. 



It appears from the foregoing that in summer the wind-produced currents are 

 relatively ineffective in more than 40 fathoms. In the spring and fall, when the 

 water is colder, currents are possible, of course, to greater depths. With no more 

 data on currents or temperatures than are at present available it does not seem profit- 

 able to speculate further on the probable effect of these factors on the movements of 

 the chubs, especially as it is not known how sensitive they are to differences in the 

 rate of water movement in their environment. 



The chub fishermen know relatively little about the spawning season of any of 

 the species. In several localities on Lake Michigan and Lake Huron alpenae and 

 zenitMcus become the objects of special fisheries during their spawning season, and 

 out of a few ports on Lake Michigan the spawning hoyi are sought for; but only 

 occasional persons here and there know anything about spawning runs of other 

 species of chubs. In fact, many of the fishermen believe that the chubs spawn all 



