280 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



PHYSICAL AND BIOLOGICAL CONDITIONS ON OYSTER-BEDS. 

 TEMPERATURE OF WATER. 



The oyster lives in waters of widely varying temperature, both as to 

 the average for the year and the extremes met with at different 

 seasons. Perhaps the greatest divergence between the extremes is 

 in Chesapeake Bay, where the range is from the freezing-point of 

 brackish water, something below 32°, to 90° F. In New Jersey and in 

 Chesapeake Bay the shallow-water oysters, which are exposed or 

 nearly exposed at low water, are frequently frozen, an event which is 

 not necessarily fatal if they are gradually thawed. Young oysters 

 in shallow water are sometimes "winter-killed," or their vitality is 

 seriously reduced, by exi)osure to exceptionally low temperatures. The 

 remedy, or rather preventive, is to remove to deeper water in the fall, 

 and seed oysters on natural spatting-grounds may often be saved by 

 this means. 



In deeper water, such as is found on the oifshore beds of Long Island 

 Sound, they are not subject to such severe trials, but are nevertheless 

 called upon to withstand, during several months, a temperature not far 

 from 32° F. In the Long Island oyster region the summer temperature 

 of the water reaches 75° F., and from May 1 to November 1 probably 

 never falls below G0° F. On the South Carolina oyster-beds the tem- 

 perature appears to rarely fall below 55° F., but, on the other hand, 

 the exposed banks of that region are subjected to the direct rays of the 

 sun and therefore withstand a temperature considerably higher than 

 that to which submerged oysters are liable. 



The temperature has an important bearing upon the food supply. 

 When the water is warm there is a rapid multiplication of the small 

 forms upon which the oyster feeds, and at the same time the activities 

 of the oyster itself are quickened. The two facts taken together result 

 in a more rapid growth of the oyster than is likely to take place in 

 colder waters. 



It is often said that "plants do not spawn," and there appears to be 

 some truth in the statement if we apply it to a period of a year or so 

 after planting, and refer to cases in which the transplanting has induced 

 considerable modification in the conditions under which the oyster is 

 placed. This fact is no doubt largely due to the changes in temperature 

 to which the oyster is subjected when transplanted. Dr. Ryder says: 



A very short exposure of the animal to water of an increased temperature caused 

 a deterioration of the generative matter. I have tried to fertilize the eggs of num 

 hers of oj'sters that had lain over night m the Quinnipiak River and invariably 

 failed ; the eggs in every case appeared to be overripe. Oysters taken from the bed 

 at the same time and from the same locality, but kept in a basket over night, gave 

 good results. 



The same investigator found that at Beaufort, N. C, the best results 

 m fertilization were obtained the nearer the teinpeiatnre was to 70° F. 

 Both at Beaufort and in Chesapeake Bay the embryos develop most 



