THE OYSTER AND THE OYSTER INDUSTRY. 15 



the temperature over the oyster beds falls in winter nearly to 32° F., 

 the freezing point, and in summer rises to 72° in deep water and 

 75 to 78° over the msliore beds. In Chesapeake Bay oysters in 

 certain shallow water beds withstand variation from the freezing 

 point, below 32 to 90° F.*^ In the Gulf of Mexico the usual range 

 of temperature over the oyster beds is from 50 to 90° F. The rela- 

 tion between temperature and the spaAvning of oysters has been 

 discussed on page 12. 



DENSITY OF WATER. 



The higher the proportion of salt contained in sea water the 

 greater the density. Therefore, it is common practice to estimate 

 the proportion of salt by measuring the density of the water with the 

 salinometer. This consists of a glass bulb with a narrow stem at one 

 end on which are gradings reading from 1.000 to 1.031. The bulb 

 is weighted at the end opposite the stem, so that it will sink some- 

 what below the surface, leaving the stem projecting from the water. 

 The less salt in the water the less the density and the lower the 

 salinometer will sink. Fresh water is arbitrarily considered as 

 1.000 and the point on the stem of tlie salinometer to which the water 

 reaches when the instrument is placed in fresh water is so marked. 

 Grades are marked below that on the stem, the bulb rising higher 

 in the water the greater the density. The highest grade is usually 

 1.031. For convenience three bulbs are usually used, one reading 

 from 1.000 to 1.011, one from 1.010 to 1.021, and one from 1.020 to 

 1.031. Common sea water usually reads from 1.025 to 1.026 on the 

 salinometer. Oysters are found in water ranging in density from 

 1.002 to 1.025, but can not withstand densities lower than 1.007 

 for indefinite periods. In general they seem to thrive best in 

 densities between 1.011 and 1.022. 



Oysters arc not usually found out in the main body of the sea- 

 water, away from the inlhience of the fresh water from the streams, 

 where the density is 1.025 or more. It wdl thus bo apparent that 

 oysters have become adapted to a certain ranj'o of densities, and 

 natural beds have grown up at points fairly close to shore or in 

 inclosed bays where the salinity of the seawater is modified by the 

 inflowing of fresh water. 



MTJD, SILT, AND SUSPENDED MATTER.* 



A bottom composed of slightly shifting sands or of very soft mud 

 into which the adult oysters will sink a7id on which the minute spat 

 can gain no firm support is alike unfavorable to oyster culture and 

 to th(5 development of natural beds. If, however, hard objects be 

 distributed on or above such bottoms they will become collectors of 

 spat so long as they remain clean and free from slime or sediment, 

 and if it be desired to produce permanent beds or to catch the float- 

 ing spat for the purpose of seeding other beds it is manifest that, 

 the scouring acticm of the currents being equal, waters containing 

 a minimum of sedimentary matter are to he preferi'ed to thoso more 

 or less laden with mud. 



"Moore, H.F. (1897, p. 280.) 



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



