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BULLETIN OF THE BUREAU OF FISHERIES 
is interesting to note, for instance, that in certain localities having an established 
reputation as excellent growing grounds, setting does not take place, in spite of 
high temperature of the water and the presence of large numbers of ripe adult 
oysters. Such, for instance, is Cotuit Bay in Massachusetts, where, according to 
the observations made by the author in 1926, a few oyster larvae were found swim- 
ming in the water but they failed to attach themselves to shells planted in the bay. 
This was probably due to the fact that every shell in this bay in a period of a few 
days becomes covered with a slimy film formed by microscopic algae, rendering its 
surface unsuitable for attachment. 
One condition prerequisite for obtaining a good set is the presence of clean 
cultch, which should be planted shortly before the time of setting. In 1884 Winslow 
wrote, “Thousands of dollars would be saved annually by the oystermen if they 
would determine with any approximate accuracy the date when attachment of the 
young oysters would occur.” It has been shown by Prytherch (1929) that time 
and intensity of setting can be predicted one month in advance; his method is based 
on a study of temperature and tidal conditions in a given body of water, on the de- 
termination of the number of spawners, and on an examination of the fullness of their 
gonad development. 
The knowledge of the exact location of the setting zone is as important to the 
oyster culturist as is the knowledge of the time of setting. Observations carried 
out by Galtsoff and Prytherch in Long Island Sound, in waters of Massachusetts, 
in Great South Bay, N. Y., and along the coast of South Carolina and Georgia show 
that setting is often restricted to a very definite zone. For instance, in the tidal 
waters of South Carolina (Galtsoff and Prytherch) and Georgia (Galtsoff and Luce, 
1930), it is confined to the zone between the tidal marks, while in the Great South 
Bay, N. Y., setting takes place from top to bottom. Analyzing the factors con- 
trolling setting in Milford Harbor, Prytherch (1929) arrives at the conclusion that 
the distribution of the setting zones can be correlated with tidal changes during the 
time of setting. He finds that in Milford Harbor the zone of the heaviest setting 
coincides with the level of low slack water. Corroborating evidence is found in the 
fact that no oyster larvae swim about in the water when the velocity of the current 
is more than 18.3 centimeters (0.6 feet) per second. Whether the setting at a definite 
level is due only to the changes in velocity of the current during the tidal cycle or 
can be correlated with the changes in the composition of the sea water at different 
stages of tide, is a problem for further research in which the authors are engaged. 
METHODS OF SPAT COLLECTION 
One of the most popular methods of collecting spat or seed oysters consists in 
scattering clean shells over the bottoms where setting is expected. This method 
was first introduced in Connecticut in 1855 when, according to Brooks (1905, p. 
105), shells were planted among the islands off the mouth of Norwalk River; since 
that time this method has been extensively employed in northern waters. In certain 
localities — for instance, Wellfleet Harbor, and in some parts of Long Island Sound- — - 
gravel and crushed stone have been planted with very satisfactory results. It was 
soon discovered that the time of planting is of great importance, since the shells 
after being submerged for even a few weeks may become covered with a slimy 
film that prevents the attachment of the oyster larvae. It is of great importance, 
therefore, to begin the planting just before the time of setting. In Long Island 
Sound this is always done between the 15th of June and 15th of August. Inasmuch 
