OYSTER INVESTIGATIONS IN GEORGIA 



91 



salinity of tlie water on April 21 i-anj^cil from 7.8;> per millc at 

 4 p. m. — approximately 90 minutes after low waiter — to 26.22 per 

 miile at 9 a. m. — approximately W minutes after the mornin*^ high 

 water. Samples of water were taken from the surface and fiom 

 2 feet above the bottom. At 7 a. m. the surface salinity w^as 17.21 

 per mille; at 8 a. m., 22.01; at 9 a. m., 28.78; then it dropped slowly 

 to 9.()8 at '^ p. m.. 7.92 at 4 p. m., and then i-ose rai)idly to 20.4G at 

 7 p. m. The bottom salinity was appreciably greater but followed 

 the surface salinity in the form of its curve. For instance, at 9 a. m. 

 the bottom salinity Avas 2G.22, while the surface salinity was 23.78. 

 The difference in "salinities was even greater on the flood tide ; for 

 example, at 5 p. m. the bottom salinity was 18.64, wdiile the surface 

 salinity was only 8.84. When ob.servations stopped at 7 p. m., the 

 difference between the top and bottom samples ranged from 4 to 6 per 

 mille. These figures show^ that at the time of the observations there 

 was a good flowof fresh water at the surface of the tidal stream. 



SPAWNING AND SETTING OF OYSTERS NEAR DOBOY ISLAND 



At the beginning of observations on June 22, 1928, oysters around 

 Doboy Island were ripe, and the temperature of the w^ater Avas above 

 26° C. (79° F.) As the spawning of the oyster may occur at any 

 temperature above 20° C. (68° F.), it is possible that oysters began 

 to spawn early in June. The first oyster larvae (straight-hinge stage) 

 were found in plankton on June 28. It is interesting to note that 

 throughout the season the larvie were rather scarce and their occur- 

 rence in i^hinkton irregular. Quantitative plankton samples were 

 taken at both high and low water from the surface and at the bottom 

 of the channel at Doboy Island by means of a pump, and the water 

 (150 gallons each time) was strained through bolting silk No. 20. 

 There were, unfortunately, numerous gaps in the collections of 

 quantitative plankton samples caused by trouble with the motor 

 which operated the pump. The results of the observations, pre- 

 sented in Table 5, show that the maximum number of oyster larvae — 

 423 per 100 gallons — w-as found on July 4. A few larvae of various 

 sizes continued to be present in plankton until August 9. With the 

 beginning of freshets during the second half of August the larvae 

 disappeared. 



Table 5.- — Occnrretiec of oyster lanxe in plankton 



' 15 umbo stage. 



2 All umbo stage. 



