72 DEPARTMENT OF THE NAVAL SERVICE 
7 GEORGE V, A. 1917 
expedition, judging by the eye of the fractions. No accuracy beyond 10 microns 
was possible, and we rarely strove for an accuracy beyond 20 microns. Thus all our 
measurements fall into groups separated by 20 microns, which gives the false impres- 
sion that the fry were produced in corresponding broods. There is no doubt that 
broods do exist, but it is necessary that the entire attention be focused on this aspect 
of things, in order properly to establish the number and sizes of the respective broods. 
We had to choose between covering a small field of observation thoroughly and 
accurately, or the reverse; aud we deliberately chose the latter alternative, as the 
logical thing to do, beginning with the general and specializing on such parts as the 
general survey showed to be worthy of additional work. Of course, a complete 
uncovering of oyster biology cannot be expected in one month or one season, ‘hence 
the finer work remains yet to be done. 
But the table does indicate some things of practical value, and that is why it is 
introduced. It will be noticed that fry, ready to set, were not observed in fair abun- 
dance until August 16. Indeed, the largest recorded for the 5th, 10th, 14th, and 16th, 
represents a regular advance in growth of 240 microns in twelve days, or 20 microns 
per day, which gives seventeen days as the minimum length of life of the floating 
larve. This length of life is quite to be expected under the influence of the higher 
range of temperature, 72 to 74 degrees, recorded. But a large proportion of the fry 
exist in temperature averages of less than ‘0 degrees; and there is inde- 
pendent evidence! showing that the period of free life of the fry in Richmond 
bay is over three weeks. It is not unreasonable to suppose that some of the fry may 
grow even slower than this rate. The rough survey marks out the boundaries of special 
problems that call for more accurate researches, on the rate of growth. Another feature 
indicated by the table, is the distribution of spawning. Spawning began late in July 
or early August, and was practically continuous throughout the greater part of 
August, with a climax at the 20th. Not only does an individual oyster use a consider- 
able period for ejecting its spawn, but the individuals on a bed do not mature at the 
same time. Further, it is evident that as the oyster beds of the bay are subjected to 
different ranges of temperature. the different beds do not propagate simultaneously. It 
follows, therefore, that spatting is also a more or less drawn-out affair, although there 
are special favourite days for spatting as for spawning, dependent on weather, as 
shown by our New Jersey: researches. These researches also have shown that 
not all the broods of fry that appear successively, reach the spatting stage 
successfully. This is another problem demanding research. The practical aspect of 
this question lies in the fact that ecultch, to be most useful, must be clean, and to be 
clean must be placed closest to spatting periods. It follows that cultch planting should 
be periodic, and that the periods should be regulated by the general weather and special 
plankton reports of the locality proposed to be shelled. For further discussion of 
spawning and spatting see those sections farther on. 
TEMPERATURE SUMMARY. 
Temperature is a factor of supreme importance in oyster life. The warmth of the 
water depends on depth, character of bottom, distance from inlet, direction of winds, 
temperature of the air, and on the sunshine. The highest temperature was 76° F., 
observed once on the flats off Tilton creek; but 74° F., was found &t the head of Bide- 
ford river, in Shemody creek, in Indian river, in the head of the bay, in Oyster creek, in 
Barbara Weit river, part of the time at Grand River bridge, and near Southwest Creek 
bridge. This is only 6 degrees above the minimum for oyster propagation, and the 
main areas of Richmond bay fail to reach this maximum. Thus, 72 degrees was 
recorded in the upper Grand river, Trout river, Bideford river, off Plat river, lower 
part of Shemody ereek, and off Barbara Weit river, Oyster creek, and the mouth of 
1See Stafford. ‘‘The Canadian Oyster,” 1913, pp. 88 and 84. ‘his excelient memoir is a 
very full exposition of the biology of the oyster. 
