PRODUCTION AND COLLECTION OF SEED OYSTERS 
201 
conservation department of 1923, the quantity of set produced by artificial propaga- 
tion was equal to approximately one bushel. The conclusion seems to be inevitable 
that the practicability of the artificial propagation of oysters has not yet been dem- 
onstrated. Apparently, the New York Conservation Commission later on reached 
the same conclusion, because in the report of 1927 on page 340 it states: “The New 
York State oyster growers suffer from the lack of oyster set. Most of the seed used 
is brought in from Connecticut or other States. This is a big handicap, and a remedy 
is eagerly sought for.” It is the author’s opinion that present methods of artificial 
propagation of oysters are very valuable for laboratory and experimental study of 
the life history of the oyster, and it seems possible that in the future, when the pro- 
cedure is simplified and the market price of seed oysters is higher, they can be made 
applicable for the practical needs of the industry. The immediate problem, how- 
ever, is to find out means and methods to increase productivity in natural areas 
rather than to experiment in the line of artificial propagation. 
SPAWNING AND SETTING OF OYSTERS 
It has been known for many years that setting in northern waters is subject 
to wide fluctuations. Oyster growers have attributed the failure of oysters to set 
to various factors: Adverse weather conditions before and after the time of spawn- 
ing, tides, currents, sedimentation, natural enemies, etc. In spite of a great variety 
of opinions expressed, the problem has been very little studied and the scientific 
literature on the subject is surprisingly meager. In discussing spawning, fertiliza- 
tion, and development of the oyster, the earlier investigators (Brooks, 1905; Ryder, 
1881, 1882, 1883, 1884; and Stafford, 1913) gave but little attention to factors which 
might affect these phenomena. Nelson (1920), studying oyster culture problems 
in New Jersey waters, states that adult oysters do not spawn in New Jersey waters 
until the temperature has reached 21.1° C. (70° F.) and has maintained it for some 
time. Nelson believes that free-swimming larvae are very sensitive to temperature 
changes and that a fall of several degrees in water temperature may cause the death 
of a large number of them. He states (op. cit., p. 9) that “a sudden fall in 
temperature during the setting period may completely inhibit the obtaining of a 
set.” 
Churchill (1920) and Gutsell (1924) state that oysters may spawn when the 
water reaches a temperature of 20° C. (68° F.) but that spawning proceeds at 
normal speed only when the water is 21.1° C. or above. According to Galtsoff 
(1930), temperature is not the only factor that controls the discharge of the sex 
products. Working under laboratory conditions, he found that the presence of 
sperm in the water induces the female oyster to spawn, the reaction taking place at 
the temperature of 20° C. and above. The eggs discharged by the female in turn 
induce the spawning of the males, and the process once started in one place con- 
tinues throughout the oyster bed. Thus, the mutual stimulation of the opposite 
sexes plays an important role in the propagation of the oyster. 
The failure of oysters to set was attributed not only to low temperature of water 
but also to the presence of enemies destroying the oyster larvae. Nelson (1925) 
thinks that the ctenophore, Mnemiopsis leidyi, which occurs in great abundance in 
the inshore waters, is responsible for the disappearance of oyster larvae and the 
absence of set in certain areas of New Jersey waters. 
Our present knowledge of the biology of the oyster is not sufficient, however, 
to explain the role of the other factors which may affect spawning and setting. It 
