SPAWNING AND SETTING OF OYSTERS 
59 
of water temperature were obtained over the period of six months from the end of 
February to the end of August, 1929. 
Over the same period samples of water were taken at noon daily from the end 
of the pier and tested for salinity and hydrogen-ion concentration. Salinity was 
determined by means of specific gravity hydrometers, and hydrogen-ion concentration 
was tested colorimetrically by means of LaMotte comparators using phenol red, 
cresol red, and thymol blue as indicators. These results were not corrected for the 
small error due to salt variation. 
Samples of plankton were taken as frequently as possible at 3 stations (fig. 5, 
stations 1, 2, and 3) in Offatts Bayou, 3 (fig. 4, stations 4, 5, and 6) in West Bay, and 
1 (fig. 3, station 7) in East Bay. A plankton net of No. 20 bolting silk was towed at 
slow speed for five minutes at each station and the sample preserved in formalin for 
Figure 4.— Chart showing a portion of West Bay including plankton and shell-planting 
stations at the Deer Islands and near the mouth of Offatts Bayou. For stations in the 
bayou see Figure 5. (From U. S. Coast and Geodetic Survy Chart No. 1282) 
analysis in order to establish the relative abundance of oyster larvae and of diatoms. 
Whenever possible water samples were brought from the vicinity of Deer Islands 
(station 5) and Hanna Reef (station 7) and tested for pH and salinity. In this ' 
manner records were obtained which showed the physical characteristics of the water 
as well as the abundance of oyster larvae and diatoms throughout the major part of 
the spawning season. 
As a means of determining when setting of oyster larvae takes place, oyster shells 
were planted periodically on the reefs at stations 1 and 2 in the bayou, station 3 at 
the Deer Islands, and station 4 on Hanna Reef. The shells were placed in bags, which 
were made of K-inch mesh poultry wire and held about a half bushel of shells each. 
(Fig.l.) Descriptions of such bags have been published by Prytherch (1930a). 
Shells from the Bolivar cannery were used because they were thoroughly clean. 
By planting these bags of shells periodically in favorable places it was possible to 
determine when setting occurred. There was no possibility of the shells becoming 
slimy, for they were frequently exchanged. 
