THE OYSTER AND THE OYSTER INDUSTRY. 17 



oyster might become exhausted. Cmrents keep the material agi- 

 tated and cause a fresh supply to sweep across the oyster beds. 



Movement of the water also brings a fresh supply of oxygen to 

 the oyster which aerates the blood by oxygen derived from the water 

 passed through its gills. 



DEPTH OF WATER.*^ 



The known vertical range of oysters under natural conditions is 

 from or near high-water mark to a depth of about 130 feet, the 

 latter extreme occurring over densely stocked and productive beds 

 in Patuxent River, Md. In a large part of the oyster region of 

 South Carolina the natural beds occur almost exclusively between 

 high and low water marks, and some of the beds of Florida are 

 similarly situated, the oysters growing on the aerial roots of man- 

 groves, as they frequently or generally do in Porto Rico and others 

 of the West Indies. In places on the Gulf coast 03'sters set and 

 grow in limited numbers in the gi-ass on the ed^es of the marsh 

 prairies above the level reached by many hi^h tides, but in such 

 situations they are frequently killed by freezmg. 



In the Mississippi delta region a good set is often obtained on 

 cultch planted at or near high-water mark, but the young oysters 

 are removed to deeper water before cold weather arrives. 



Elsewhere oysters are rarely planted in this country on bottoms 

 exposed at low water. In most places comparatively shallow depths 

 ranging from 2 to 12 or 15 feet are utilized in oyster culture, but in 

 Long Island Sound the practice has been successfully extended to 

 depths of 60 feet or more. 



FRESHETS, STORMS, AND ICE.** 



Freshets occur with more or less frequency in the rivers discharg- 

 ing near the oyster beds of many of ttie South Atlantic and Gulf 

 Coast States, and with them are to be classed the crevasses or breaks 

 in the levees which sometimes accompany high water in the coastal 

 streams of Louisiana. 



Tlie effects of a freshet are twofold. The most immediate effect 

 is that, owing to the vastly increased volume of fresh water dis- 

 charged, the salinity of the water over the oyster beds is reduced 

 far below the normal and in many cases becomes fresh or practically 

 so for considerable periods. As already stated in another connec- 

 tion, this is often fatal to the oysters already on the beds, and, even 

 when this is not the case, the production of a set is inhibited during 

 the prevalence of the abnormal conditions. 



Freshets also carry large quantities of mud and debris scoured 

 from old channels and washed from the land, and as the currents 

 slacken in the bays and estuaries, where the oyster abounds, their 

 carrying power diminishes, and the materials are dropped on the beds. 

 If the deposits so made be deep, the old oysters may bo killed, while 

 even a light deposit is sufficient to prevent the attachment of spat 

 until it be again gradually scoured from the shells and other hard 

 bodies on the bottom. 



a Moore, H. F. Proposed revision of "Oysters and Methods of Oyster Culture" (1897). 



