LIFE HISTORY OF LAKE HERRING OF LAKE HURON 



399 



a study of the air temperatures remains tlic same. Table 62 shows, in degrees Fahren- 

 heit, for the months of April to Novemher, inclusive, for the years 1913 to 1922, 

 the mean monthly air temperatures at Saginaw, Mich. They were taken from 

 the various reports of the chief of the United States Weather Bureau. The mean 

 of the monthly averages of each year is shown in the last column of the table, while 

 the mean of each month of the several years is given at the bottom of each column. 

 To make comparison of these temperature data easier and more accurate, I deter- 

 mined, by means of a polar planimeter, the area inclosed by each curve plotted from 

 the monthly averages for each year, employing as the base line a line drawn through 

 39.2° F., the temperature at which water reaches its maximum density. The result- 

 ant values express roughly the relative amount of heat available from the air for 

 each year for the months April to November, inclusive. These values are arranged 

 in Table 63 in order of size. It may be noted, when a comparison is made, that the 

 order of the years, based on the size of the planimeter measurements differs only 

 slightly from that based on the magnitude of the annual averages of the mean monthly 

 temperatures. 



Table 62. — Mean monthly air tempernlnres, in ° F., of April to November, 1913 to 1923, inclusive, 

 taken at Saginaw, Mich., by the United States Weather Bureau 



Table 63. — Area included in curve based on average monthly air temperatures of Saginaw, Mich., 

 for period April to November, 1913 to 1922, inclusive [Table 62). The base line employed is the 

 line drawn through 39.2° F. 



We know nothing specifically about the relation of temperature to growth rate 

 in the herring or about optimum temperatures for the growth of the herring; but if 

 we assume that, other factors remaining constant, the year with the warmest growth 

 season produces the largest and fastest growing fish, we ought, then, to find that the 

 herring in Saginaw Bay grewjnost rapidly in 1921 and least rapidly in 1917, and that 

 the growth rates of the other years fluctuated in general as the average temperatures 



