PROGRESS IN BIOLOGICAL INQUIRIES, 1937 45. 



cipal investigations carried out at the Milford, Conn., laboratory by 

 Dr. V. L. Loosanoff and James B. Engle. To obtain a broader knowl- 

 edge of conditions governing the survival of oysters in the Sound and 

 its tributaries, a study of the physical and biological factors was 

 undertaken on a much larger scale than had been carried out during 

 previous years. 



For observations on temperature, salinity, conditions of oyster 

 gonads, presence of larvae in the water and their setting at various 

 depths, 23 stations were established in Long Island Sound proper 

 from a ]:)oint opposite the mouth of Saugatuck River in the west to 

 Joshua Point in the east. AH these stations were visited every week 

 during the spawning and setting season. 



Regardless of the fact that much work on the biology of the oyster 

 has been carried on in local waters, no attempt has ever been made to 

 conduct a systematic study of oyster setting in Long Island Sound 

 proper. To fill this gap it was decided to determine the beginning and 

 end of the setting period, the intensity of setting throughout this 

 period, the intensity in relation to depth, the correlation between set- 

 ting and the temperatures and salinity of water, and finally, the rate 

 of survival of recently set oysters in different parts and in different 

 depths of Long Island Sound. For these studies two oyster-seed pro- 

 ducing areas located about 5 miles a})art were chosen. The so-called 

 Stratford Point area represented the natural oyster beds where little 

 or no cultivation of oysters is carried on. Welch's Point area, on the 

 other hand, was located in the center of cultivated grounds. In the 

 studies of setting in each area, wire bag collectors of uniform size and 

 containing approximately the same number of shells were used. The 

 bags were removed from the water at semiweekly intervals and 

 replaced by unused duplicates. 



From the analysis of this year's observations as well as from the 

 information already in the files of the station it may be concluded that 

 the salinity of bottom water, wliich is subject to only slight seasonal 

 changes throughout the 3^ear and remains virtually the same from year 

 to year, is not a factor responsible for the success or failure of spawn- 

 ing and setting of oysters in the Sound. It was also noted that during 

 the summer of 1937 spawning occurred at a temperature of less than 

 20.0° C. (68° F.) which had been regarded previously as the minimum 

 temperature required to induce this act under natural conditions. The 

 first and general spawning of oysters in the Sound took place on July 

 2 and 3. It was followed by a setting which was first recorded on 

 July IT. Subsequent heavy settings in July and early August con- 

 tinued without interruption for 3 weeks. The last and rather light 

 setting occurred on September 20. Examinations of spat collectors 

 disclosed that setting took place from mean low water to a depth of 70 

 feet, but was heavier in shallow water. The first set in some places 

 amounted to 10,000 spat per bushel, but mortality caused by attacks 

 of starfish and drills ranged from 93 to 100 percent. 



To assist the oyster growers of Long Island Sound in obtaining the- 

 best set, information accumulated by the laboratory staff was sum- 

 marized and issued in Aveekly bulletins which were distributed through 

 the cooperation of the Connecticut Shellfisheries Commission. The 

 bulletins contained statements regarding the condition of oysters,, 

 changes in water temperature, and expected time of spawning and 



