80 
BULLETIN OF THE BUREAU OF FISHERIES 
of particular significance with regard to oysters in most of the Gulf of Mexico waters, 
since most oysters occur at approximately the low-tide level and few are found in 
deeper water. 
Whatever may be the significance of the correlation between temperature fluc- 
tuations and the abundance of diatoms at the surface, the graphs (figs. 8 and 19) 
show distinctly the gradual disappearance of diatoms between March and August. 
This is entirely in harmony with the well-known seasonal variation in diatom growth. 
Steuer (1903) called attention to the fact that while in northern waters there are two 
maxima of diatom abundance, one in spring and one in the fall, in more southern 
waters the two maxima encroach more and more upon the winter months, thus 
tending to fuse together in warm regions to form a single winter maximum. This 
condition was found in the Adriatic. A secondary maximum was found to occur in 
June and July. Fish (1925) found essentially the same condition to obtain in 
Buzzards Bay. 
Since this variation is a function of temperature, and since the warmer the water 
the greater the tendency to concentrate the maximum into the winter months, it 
would be expected that in the very warm water of Galveston Bay the maximum 
would be of relatively short duration, perhaps in mid or late winter, depending upon 
the time of minimum temperature. It would be of considerable importance in 
reaching a complete imderstanding of the differences between oysters of the North 
Atlantic coast and those of the South Atlantic and Gulf coasts to obtain systematic 
diatom collections throughout the year. It may well be that the short season during 
which oysters in the southern waters are fat or prime is due as much to a short period 
during which sufficient food is available as to the long spawning season. The obser- 
vation of Battle (1892) on oysters in South Carolina waters is of significance in this 
respect. He wrote (p. 329) : "As a rule the oysters do not attain their best condition 
in South Carolina until late in the winter and early in the spring.” Yet the spawn- 
ing season there, as in Texas, probably ends in late fall. It is very probable that the 
oysters do not become prime until relatively late because of the lack of food in fall 
and early winter, and that the period of maximum “fatness” of the oysters corre- 
sponds closely with the period of maximum abundance of diatoms. 
USE OF WIRE BAGS OF SHELLS AS CULTCH 
In South Atlantic and Gulf waters one of the major difficulties in obtaining seed 
oysters is due to the fact that silt and slime soon cover the cultch after it is placed 
in the water. As has been discussed in the preceding pages, the setting periods in 
Galveston Bay were scattered and of short duration, although setting might be ex- 
pected at times during at least six months ’of the year. Had shells been placed in the 
water at the middle of April when a set was expected, the shells would have become 
silted and their value as cultch in this manner reduced before any setting took place. 
For this reason the simple method of spreading shells on suitable bottom is inadequate 
especially when the setting does not occur soon after the planting of the shells. One 
aim of the present investigation was to determine whether the method of using wire 
bags of shells as cultch is suitable in such a body of water as Galveston Bay. A 
complete account of experiments with these bags on the Atlantic coast has recently 
been published by Galtsoff, Prytherch, and McMillin (1930). 
As has been described, the set obtained on shells in such bags in Galveston Bay 
was highly satisfactory. Table 3 shows the number of spat per bag of shells obtained 
