444 



BULLETIN OF THE BUREAU OF FISHERIES 



daily air temperature reaches its annual maximum during the period from July 10 to 

 August 5. This is true for the water temperatures, also, as the trend of the two is 

 approximately the same during the annual cycle. 



In comparing the monthly mean temperature of the air with that of the water 

 in Milford Harbor, we find that during the summer months the air ranges only 

 from 1 to 2 degrees higher. This relationship can be used as the basis for esti- 

 mating the approximate water temperatures over a period of six years (from 1922 

 to 1927) when thermograph records were not available. Obviously, when air tem- 

 peratures are above normal the water is correspondingly warmer, and when they 

 are below normal the water temperatures are noticeably lower. Thus, analysis of 



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MONTHS 



i. — Monthly departure of air temperature from normal, as shown by records of the United States Weather Bureau, 

 Haven, Conn, The normal mean temperature, in ° F., for April is 46.9; May, 57.8; June, 66.6; and July, 72 



the mean monthly air temperatures for any year will indicate the probable water 

 temperatures that occur in small, partially inclosed basins. For this purpose the 

 departure of the air temperature from normal can be used as an index to the pre- 

 vailing conditions. The monthly departures of air temperature for April, May, 

 June, and July of each year from 1922 to 1927 are presented in Figure 8. In April 

 the water temperature reaches a degree at which the oyster resumes feeding after 

 having been in hibernation since November, and, consequently, we are interested 

 in temperature conditions from this time until spawning occurs in the latter part 

 of July. The monthly differences in air temperatures occurring during this period 

 in each of these years are at once apparent, and when they are summarized for 

 the entire period we find that for three of the years the temperature was above 

 normal and for the other three below. The significance of these departures is dis- 

 cussed later in connection with their effect on spawning and setting. 



