INVESTIGATION OF OYSTER SPAWNING, ETC., MILFORD, CONN. 435 



we find that at several points between the upper and lower boundaries of the natural 

 beds in each section the productivity and abundance of the oysters show wide varia- 

 tions. As a general rule, oyster growth and seed production are best in a zone about 

 halfway between the upper and lower limits of a natural bed and least at the extremes, 

 which can be correlated with variations in the physical conditions found in different 

 parts of the bed. However, if we take the natural beds as a whole, or the cultivated 

 beds, we find great fluctuations in the quantity of seed oysters that they produce 

 from year to year. Their production often ranges from over 1,000,000 bushels, as 

 was the case in 1925, to virtually none, as in 1926 and 1927. The study and com- 

 parison of the physical conditions in 1925 and 1926 was made in order to determine 

 the factors responsible for these annual fluctuations in seed-oyster production. 



The potential value of any body of water for the propagation, growth, or fatten- 

 ing of oysters is determined largely by the physical and chemical conditions that exist 

 there. In some localities these conditions are more or less constant, while in others 

 they imdergo considerable variation. Each region, however, has certain physical 

 characteristics of its own, and these are representative of the combined influence of 

 the climatological, hydrographical, and physiographical conditions found there. In 

 Milford Harbor and vicinity there is a great range of variation in a comparatively 

 short distance ; and since it is a favorable location for the production of three impor- 

 tant shellfish — the oyster, quahaug, and soft clam — the various factors will be dis- 

 cussed in detail in order that they maj' serve as the basis for comparison with other 

 regions. 



TEMPERATURE 



In the environment of the oyster, water temperature is the most important 

 factor, as it controls, either directly or indirectly, the growth and reproduction of 

 the organism. It directly affects the physiological processes of the oyster, such as 

 feeding, respiration, development of the gonads, spawning, etc., while indirectly it 

 influences, to a great extent, the growth and abundance of the microscopic forms 

 that constitute the food of the oyster and oyster larvae. 



The water temperature in Milford Harbor is the resultant of the interaction of 

 the various factors that can be placed in two major groups — the climatological and 

 the hydrographical. The chief climatological factors affecting water temperature 

 are (1) solar radiation, (2) air temperature, (3) precipitation, (4) wind, and (5) per- 

 centage of sunshine. The chief hydrographical factors, in order of their importance, 

 are (1) tide, (2) river discharge, (3) tidal currents and circulation, and (4) depth 

 of water. 



The relative importance of any one of these factors can be discussed only in a 

 general way because its effect on water temperature depends largely on its relation 

 to one or more of the remaining factors. 



In Figure 3, the mean daily temperatures of bottom water are shown for July 

 and August of 1925 and 1926 and cover the period when spawning and setting of 

 oysters occur in Connecticut waters. The figures are taken from the records of the 

 thermograph placed in the harbor at Station 2, the average for each day being 

 determined by means of a planimeter. The fluctuations in water temperature that 

 occurred during these two summers are typical for estuaries and shallow inshore 



