NATIONAL FISHERY CONGRESS. 277 



exposure to a density of less than 1.005 or more than 1.022, if not fatal to the individ- 

 uals, is at least fatal to the species, as young are not produced to take the place of the 

 old ones which are dying off. 



In many places where the salinity is favorable during a large part of the year it 

 happens that at certain seasons a heavy influx of fresh water produces a temporary 

 reduction below the desired minimum. This appears to be particularly liable to occur 

 on the Gulf coast, where many great streams and innumerable small ones become 

 swollen by the rains and discharge large quantities of fresh water close to the oyster- 

 beds. Two facts, however, tend to mitigate the evil which might result. In the first 

 place the oyster is able to tightly close its shell when subjected to objectionable 

 conditions, and thereby the fresh water may be for a time excluded, and Professor 

 Washburn has recently shown that they will live for upward of ten days in the water 

 of running brooks. Then, too, the fresh water, being lighter than the salt or brackish, 

 tends to spread over the surface of the bays into which it is discharged, and it is 

 usually found that the bottom density is greater than the surface density, even after 

 long continued freshets. The changes are therefore more gradual and less radical 

 than if the salt water were driven out before the fresh, and the oyster finds conditions 

 more favorable at bottom than it would be subjected to if it were a surface-dwelling 

 organism. In selecting planting grounds the question of liability to the influence of 

 freshets should always be given consideration, as disaster may result from its neglect. 



TEMPERATURE OF THE WATER. 



Adult oysters are not ordinarily adversely affected by temperatures ranging 

 between the freezing point and 90 F. Those upon flats exposed at low water are 

 often frozen during the winter and subjected to the high temperatures of the direct 

 rays of the summer sun, and yet many of them live to a ripe old age measured by the 

 span of an oyster's life. During the spawning season, however, a temperature too low 

 or too high, or changes too sudden and too violent, will either kill the spat or prevent 

 spawning altogether. In the Long Island and Chesapeake regions cold rains and 

 periods of low thermometer are not infrequent in summer, and multitudes of oysters 

 in their swimming stage end their career in sudden adversity. On the Gulf coast 

 such fatalities are of less frequent occurrence, and the probabilities of obtaining a 

 set, other things being equal, is correspondingly enhanced. 



CHARACTER OF THE BOTTOM. 



To be suitable for oyster-culture the bottom should be of such consistency as will 

 prevent the oysters becoming engulfed in the mud or covered by shifting sands or 

 ooze. The several surveys that have been made of the Gulf coast by the Fish 

 Commission indicate that suitable bottom, unoccupied by a natural growth of oysters, 

 may be found with but little effort. These sections of our coast, however, appear to 

 be rather more liable than the northern oyster grounds to shiftings of the bottom by 

 stormy seas, and the prospective oyster-grower should not be misled by deceptive 

 appearances, as a loose sand in shallow water exposed to heavy or even moderate 

 wave action may in a short time change its location in a manner disastrous to the 

 planter. With large areas of suitable bottom open to occupation, it is not necessary 

 to point out to the Gulf coast oyster-grower the means by which his Connecticut 

 brother has made available to his purposes many thousand acres of bottom by nature 

 wholly un adapted to the oyster. 



