400 BULLETIN OF THE BUREAU OF FISHERIES 



or heat budgets (Table 63) of these years; that is, that the growth rates of a relatively 

 cool year were lower than those of a relatively warm year, and vice versa. At firet 

 glance there appears to be some correlation between temperature and the growth 

 rate of the Saginaw Bay herring. We see from Tables 62 and 63 that the years 1919, 

 1921, and 1922 were the warmer years of the series, and from Table 39 that during 

 these years and 1920 growth was more rapid than during the years 1915 to 1918. 

 In the years 1915 to 1918 chemical substances imdoubtedly were present in Saginaw 

 Bay water that were not present before or after that period. Their effect on growth 

 rate is discussed in another place. Assuming that they had an effect, the relation of 

 temperature and growth rate might be obscured by it if years when the chemicals 

 weie present were compared with other years. It is best, therefore, to compare the 

 years 1915 to 1918 one with another and the years subsequent to 1918 one with 

 another to see whether in either period any relation is revealed between fluctuations 

 in temperature and those in growth rate. 



We may then consider the 1-year fish of each year class separately and compare, 

 year for year, their growth rate with temperature. We find, then (Table 39), that 

 the 1-year fish grew approximately at the same rate during 1915 to 1918 apparently 

 uninfluenced by the fact that the average annual air temperature dropped 4.2° F. 

 in 1917 and rose 3.5° F. in 1918 (Table 62), or, othei-wise stated, that the average 

 temperature was decreased about 20 per cent in 1917 and increased about 18 per cent 

 in 1918 (Table 63). Yet in 1919, with an increase in the average air temperature of 

 only 1.0° F., or about 8 per cent, the growth rate of the 1-year fish increased (113-116 

 to 116-127 milUmeters); and with a decrease of 1.4° F. in the average air temperature 

 (8 percent) in 1920, the growth rate of these fish increased above that of 1919 (116-127 

 to 117-139 millimetei's) . With an increase of 3.3° F. in the mean air temperature in 

 1921 (roughly 20 per cent), the growth rate increased only slightly above that of 1920 

 (133 and 139 to 136 and 142 miUimeters, respectively); and with a decrease in tem- 

 erature of 1.5° F. (15 per cent) in 1922 there was a slight increase in rate of growth. 

 Apparently, so far as these data show, there was little correlation between the growth 

 rate of the 1-year herring of Saginaw Bay and temperature during either the period 

 1915 to 1918, or, in that following 1918. We conclude that the evidence does not show 

 that temperatui'e was the controlUng factor in the alteration in the growth rate of 

 the herring of Saginaw Bay during the period 1915 (1916) to 1922. 



The amount of sunshine determines the rate of growth of phytoplanlcton and 

 consequently that of the zooplankton, on which herring feed; but the relation of 

 sunshine to both air and water temperatures is such that probably mean air temp- 

 eratures afford a good index to both. It has not been thought necessary, therefore, 

 to study the data for the purpose of determining whether any relation exists between 

 the average number of sunshine hours in various seasons and the rate of growth of 

 the 1-year herring. 



FISHING INTENSITY AS A FACTOR 



One of the best and most convincing demonstrations of the effect of intensive 

 fishing on the rate of growth of fishes is that afforded by the work of the Danish 

 biological station at Copenhagen, carried on under the direction of Doctor Petersen 

 (1922). In his survey of the plaice fisheries, covering the years 1893 to 1922, Doctor 



