INVESTIGATION OF OYSTER SPAWNING, ETC., MILFORD, CONN. 481 



water had a pH value ranging from 7.8 to 8.2 when spawning occurred, while in 

 the exceptional case the pH was 7.G and the water temperature 23° C. 



As shown in Figure 26, the pH value of the water in Milford Harbor is lowest 

 at the time of low water, when the pH is approximately 7.2, and is highest near the 

 period of high water, when the pH averages about 8.2. The failure of the oysters 

 to spawn at low tide, when the water temperature is often above 20° C, evidently is 

 due to the low alkalinity of the water at this stage of tide, as indicated by the pH 

 readings. Spawning was found to occur near the times of high water at this same 

 temperature, when the alkalinity was much higher or when the pH value was 7.8 

 or above. In 1925, the heaviest spawning took place on the day when the water at 

 the times of high tide had attained a temperature of 20° and 21.5° C, and in 1926, 

 when the temperature at the same stage of tide was 20.5° and 21° C. 



In summarizing the studies of spawning in Milford Harbor, it is concluded that 

 the most important controlling factors are the temperature of the water, the range of 

 tide, and the hydrogen-ion concentration. 



OCCURRENCE AND DISTRIBUTION OF THE hAKVJE 



For several years, studies of the oyster larvae in Connecticut waters have been 

 carried on by various investigators of the bureau (Churchill and Outsell, unpublished 

 reports), and extensive plankton collections were made in the region between Bridge- 

 port and New "Haven. In these collections the abundance and distribution of the 

 larvae were extremely irregular, and in the majority of the samples no larvae could 

 be found. In locating stations over tliis comparatively large area such a variety of 

 changes in the physical conditions is encountered that the results at each station are 

 hardly comparable and there are insufficient data for the study of any one locality. 



The plan that was put into operation in 1925 consisted (1) in the rehabilitation of a 

 natural oyster-growing body of water, such as MUford Harbor, by the estabUshment 

 of spa\vning beds and (2) in an intensive study of the occurrence and distribution of 

 the oyster larvae in this restricted area in relation to the physical conditions existing 

 there. Both quantitative and qualitative plankton samples were collected, together 

 with data as to temperature, salinity, and stage of tide. The oyster larvae were found 

 in two rather distinct groups, the first of which was rather small in number and 

 appeared on July 8 and 9 in the straight-hinge stage, which indicates that light spawn- 

 ing occurred on Jiily T-, while the second or larger group of larvae was found in the 

 water on July 14 following a heavy spawning of oysters on July 13. The duration 

 of the larval period in the first group was approximately 1 3 days , with a mean daily 

 water temperature of 20.8° C, while in the second group the period from spawning to 

 setting was Ifijiajs at a mean water temperature of 20.6° C. The completion of the 

 larval period, with setting of the larvae on the 20th and 29th of July in 1925, occurred 

 approximately two weeks earlier than had been observed at any time previous and 

 can be attributed to the higher water temperatures of that year. 



In 1925, 130 plankton samples were collected at the various stations from both 

 the surface and bottom. The results obtained from these collections were much 

 different than had been expected, and the oyster larvae not only were scarce but 

 occurred very irregularly. The majority of the larvse found were either a day or two 

 old or nearly fully developed and ready to set. The number of larvae at any station, 



