56 DEPARTMENT OF THE NAVAL SERVICE 
7 GEORGE V, A. 1917 
any practical effect? Because “it is the last straw that breaks the camel’s back,” 
and because all natural species, including oysters, exist under a balance. We have 
only to refer to the extinction of the American bison, which existed in such huge 
herds on our plains; or still better, the extinction of the wild pigeon, whose flocks in 
migration used to darken the skies of nearly a continent for days. It is absurd to 
believe that this species was hunted until the last pair was shot. The destruction by 
the hunter, great as it was in the case of the bison, or of the pigeon, was probably 
slight in comparison with all the other natural enemies, but the latter, suddenly sup- 
plemented by man, finally turned the balance, and completed the work after the hunt- 
ing ceased. Let us consider some of the destructive agencies operating against 
oysters. 
THE MEANING OF FECUNDITY. 
When the oyster ejects its millions of eggs into the water, these at first tend to 
sink to the bottom, which they would reach in ten minutes in calm water. In order 
that the eggs may develop, they must be fertilized by the male spawn or sperms. The 
sperms must be sufficiently abundant to enable an average of three hundred to cling 
to each egg during the ten minutes the egg is afloat. They must have been recently 
ejected from the male oyster or they will have died. The male oyster must have been 
ready to spawn at nearly the same time as the female, and must have lain sufficiently 
near, so that the water flowing over him shall reach the female by the time she emits 
her spawn. This is favoured by the fact that the process of spawning usually takes 
several hours or even days. We need to ascertain a good deal more than we know 
now before we can make precise statements, but we know that even where water is 
in such favourable agitation that the eggs are prevented from sinking to the bottom, 
they must be fertilized within a quarter of an hour to undergo normal development. 
This is the first reason for the enormous production of eggs. In spite of losses, vast 
numbers of developing young are started. As many as ten thousand newly hatched 
oyster fry or larve have been counted in a single bucketful of water dipped up over 
an oyster bed. But this signifies that there are other chances yet to be taken. 
COMPETITION WITH PLANKTON ENEMIES. 
After hatching, which occurs in from five to eight hours, the young oyster swims 
so weakly that the feeblest current carries it hither and thither. Indeed, all it effects 
by swimming, is to reach the surface and then to dive again, and so keep going up and 
down, requiring an hour to swim a distance of a few feet. But the oyster fry find the 
water is crowded with minute enemies, such as Copepods (water fleas), the “veligers ” 
if the many snails that cover the bottom, and a vast number of the larve of bivalves 
of various species, all capturing everything within reach small enough to enter their 
hungry maws. These enemies eat the young oysters, and the messmates consume 
their food. For several weeks the young oyster has to run this gauntlet and obtain 
sufficient food to effect an increase in volume of a hundredfold before it attains the 
spat stage in its development. Great as has been the ninefold decimation, yet so many 
survive that, if clean oyster shells be planted at the time of spatting, as many as a 
hundred or more spat may be caught upon a single shell almost anywhere upon or 
near an oyster bed. 
LOSS BY TIDES. 
This, great survival is the more remarkable when we reflect that twice daily a vast 
body of water runs over the oyster bed out to sea, carrying myriads of larve, and only 
a part of this water returns. The astonishing fecundity of the parent oysters suffi- 
ciently meets this loss also. But the struggle for life has not yet ended. 
