76 U. S. BUREAU OF FISHERIES 



corner is occupied by high hind. The channel along the western shore 

 of the island and in the North River is from 19 to 27 feet deep, with 

 very steep banks. The bottom and flats along the northeastern shore 

 of North River are hard, while soft mud prevails on the bottom of 

 the channel and on the flats farther up the river. Sticky mud is 

 found between Doboy and Commodore Islands. At high tide, sea 

 water enters the channel from Doboy Sound through the mouth of 

 North River, while fresh water from Darien River is brought in by 

 North and Rockdedundy Rivers. 



On the western shore of the island there is a dock extending nearly 

 to the channel from which daily observations of temperature, salinity, 

 and plankton were carried out. The rocks on the banks and on the 

 pillars of the dock were well covered with oysters. 



TEMPERATURE AND SALIXlTY OF THE WATER 



Daily observations of temperature and salinity of the water made 

 during the period from June 22 to August 31, 1928, are shown in 

 Figure 11 and Table 2, together witli the data on precipitation and 

 maximum and minimum air temperatures. The latter were taken 

 from the records of the nearest meteorological station, at Brunswick. 

 An examination of Figure 11 shows that by the end of June the 

 water temperature was already above 26° C (79° F.) and that it 

 remained around this figure throughout the summer. The curves of 

 maximum and minimum air temperatures remained at their respec- 

 tive levels Avithout showing any definite rise or fall. As would be 

 expected, their fluctuations from day to day were more pronounced 

 than those of tlie w^ater temperatures. 



These thermal conditions, typical for the coastal region of Geor- 

 gia, the climate of which is characterized by long, hot summers dur- 

 ing which the clianges in temperature from day to day are very 

 small, are distinctly different from those observed in Long Island 

 Sound and other inshore areas of the North Atlantic States, where 

 during the sunnner the temperature of the water gradually rises 

 until it reaches its maximum, usually during the second or third 

 week of August. The fact that water temperature in Georgia 

 remains nearly constant throughout the summer must have a pro- 

 nounced effect on sjiawning of oysters. It has been shown by the 

 experiments of Galtsoff (1930) that temperature is one of the 

 important factors stimulating the discharge of the sex products by 

 the oysters. Prytherch (1929) has demonstrated that spawning of 

 oysters in Long Island Sound usually is coincident with the rise of 

 temperature of the water. These observations were confirmed by 

 Galtsoff (unpublished reports) for Wareham River and Onset 

 Mass., where it has been noticed that oysters begin to spawn a' most 

 simultaneously after the temperature has reached its highest point. 

 It is permissible to assume that in the localities when the tempera- 

 ture remains nearly constant for a period of several months environ- 

 mental changes other than temperature may enter into play and 

 become the controlling factors. ■ Unfortunately, observations at 

 Doboy Island began rather late (end of June), when the tempera- 



