INVESTIGATION OF OYSTER SPAWNING, ETC., MILFORD, CONN. 495 



PREDICTING THE INTENSITY AND TIME OF OYSTER SETTING => 



The production of seed oysters on both the natural and cultivated beds in 

 Connecticut has fluctuated tremendously from year to year; for example, from over 

 1,000,000 bushels in 1925 to virtually none in 1926 and 1927. 



The present investigation has shown that the physical conditions in 1925 were 

 decidedly different than in 1926 and could be correlated with the quantity and 

 ripeness of the spawn in the oysters, the time of spawning and setting, and the 

 intensity of setting or quantity of seed oysters that were produced each year. 



The data on the various factors have been presented, analyzed, and discussed 

 as to their effect on the oyster and oyster larvee and the environmental conditions 

 over the oyster beds. Of the many factors involved, water temperature has been 

 found to be the most important in controlling the development and ripening of the 

 gonads and in determining the time of spawning and setting. The studies have 

 shown that the success or failure of setting and its intensity depend largely upon the 

 departures of temperature from normal. As is shown in Figure 28, during the past 

 six years setting in Long Island Sound has been successful when the temperature was 

 above normal and has failed when it was below, for the period April to August. 

 Another important factor is the relationship between the range of tide and the 

 increase in water temperature to 20° C. and above, which is necessary to induce 

 spawning of the oyster. 



The present investigation would not be complete without a discussion of the 

 economic and practical value of the results that have been obtained. The most 

 important application that can be made is in predicting the intensity and time of 

 oyster setting in Connecticut waters. A method or plan of procedure has been devel- 

 oped for the purpose of determining or predicting, one month in advance, (1) the 

 relative intensity of setting that will occur and (2) the time when spawning and setting 

 will take place. The fundamental principle of the method is a comparison of the 

 records of the present season with those of the preceding years for which the time 

 of spawning and yield of seed oysters is known. The predictions can be made from 

 about the 1st to the 10th of July of each year after careful consideration has been 

 given to the following conditions: 



1. The quantity of adult oysters on the beds. 



2. Water temperature from April to July. 



3. Quantity and degree of ripeness of the spawn. 



4. The range of tide for July and August, as shown in the tide tables. 



The first condition obviously is important and can be determined without diffi- 

 culty from the planting records of the oyster-growing concerns or by examination of 

 the oyster bottoms. This factor is of great significance because it is multiplied by 

 the quantity of spawn per oyster and gives the approximate total quantity of spawn 

 that can be discharged into the water. 



The second condition, water temperature, preferably should be determined by 

 a thermograph, although an approximate estimation can be made as to its departure 



1 Predictions in regard to oyster spawning and setting in Connecticut waters were made on July 1, 1928, using as a basis the 

 conditions herein described. The light general set that was predicted to occur on Aug. 11 did talse place at that time and in the 

 quantity anticipated. On the beds off Stratford Point and Bridgeport the set on Aug. 11 averaged 10 spat per shell, while ofl 

 New Haven an average of 12 spat per shell was found on Aug. 15. 



