448 BULLETIN OF THE BUREAU OF FISHERIES 



fluctuations are greatest, and the daily average shows a steady increase. We can 

 define the full-moon tidal period as the interval between the first increase in tidal 

 range following first quarter of the moon to that which follows the third quarter of 

 the moon. The length of this period is approximately 15 days, half of which occurs 

 before the time of full moon and the other half after full moon. During the first 

 half of the full-moon tidal period, the tide in Milford Harbor gradually increases in 

 range from approximately 6 feet to 8.5 feet, while during the second half it gradually 

 decreases from day to day until the range is again approximately 6 feet. 



The area of tidal flats that are flooded at the time of high water or exposed at 

 low water is smallest at the beginning and end of this period and largest at the 

 middle, when the range of tide is greatest. Similarly, the eft'ect of solar radiation 

 and air temperature on temperature of the water is greatest when the range of tide 

 is highest, because of the greater surface that is exposed. 



The rate of increase in the daily water temperature and the maximum degree 

 attained during the fufl-moon tidal periods in July, 1925 and 1926, are shown graph- 

 ically in Figure 11. During this period in 1925, the water temperature increased 

 from 15.8° C. at the beginning to 24.8° C. at the end, a rise of 9° in 15 days. Under 

 virtually the same conditions in 1926, the water temperature increased from 18.2° C. 

 to 26.4°, a rise of 8.2° in the same period of time. The similarity of the changes in 

 the daily temperature as recorded by the thermograph at the beginning and end of 

 this period in 1925 and 1926 is also shown in Figure 11. The maximum temperature 

 reached by the water during the full-moon tidal periods depends upon three general 

 conditions, namely, (1) the temperature of the inshore water at the beginning of 

 full-moon tides, (2) the temperature of the ocean water brought in by the tides, 

 and (3) weather conditions during this period. The first two conditions can be de- 

 termined by direct observations and will vary from year to year in accordance with 

 weather conditions in the preceding spring months. The temperature of the ocean 

 at the mouth of the Sound attains its maximum, which is approximately 18.5° C, 

 from about the 15th of July to the 15th of August. There are, however, noticeable 

 annual differences, of which the 1925 and 1926 records, shown in Figure 12, are good 

 examples. When the ocean temperature has attained 18° or 20° C, its cooling 

 effect on the waters of Long Island Sound during spring tides is not very great and 

 is more than counteracted by the flooding and warming of the water on a much 

 greater area of tidal flats. The third factor, weather conditions, can not be predicted 

 definitely, but an analysis of the meteorological data for many years, as presented 

 in Figure 5, shows that during this period one should expect maximum intensity of 

 solar radiation, maximum number of hours of sunshine, and the maximum air tem- 

 peratures for the entire year. The influence of intense solar radiation and high air tem- 

 peratures combined with greatly increased tidal range is responsible for the heating 

 of the water to a temperature of 20° C. and above during this period. Though the 

 water in the Sound does not warm as rapidly nor reach as high a temperature as 

 that in the harbors, it follows closely the trend of the inshore-water temperatures. 



In studying the hourly fluctuations in water temperature, we can readily see 

 the actual changes that occur with spring and neap tides and at different stages of 

 the tide, examples of which are given in Figure 13, for the periods July 24 to 26, 

 1926, and August 2 to 4, 1926. The greatest hourly fluctuations occur with spring 



