NATURAL OYSTER BEDS OF DELAWARE. 



27 



to foresee. Oysters can not set on the mud. They must have some 

 hard, clean object to which to attach when they settle down from 

 their infantile free-swimming habit, and on the beds the old shells 

 and the oysters themselves offer the only possibilities. If there be 

 few or no shells the recuperation of exhausted beds is correspondingly 

 retarded. If both shells and oysters are persistently removed, the 

 most productive bed eventually will be hopelessly depleted. 



PHYSICAL AND BIOLOGICAL CONDITIONS. 

 TIDES AND CURRENTS. 



A staff tide gauge was established at the wharf at Mahon River 

 Light-house and readings were taken hourly from 8 a. m. until 5 p. m. 

 during the period of the survey. This does not furnish a very accurate 

 plane of reference, but as the location of the gauge was central with 

 respect to the more important beds it is sufficiently accurate for the 

 purposes of this report. The average rise and fall of the tide between 

 June 19 and July 10 was 5.4 feet, the minimum being 4.5 feet on July 

 10 and the maximum 6.3 on July 2. 



No measurements of the velocity of currents were made, but in 

 general it may be stated that they are strong throughout the region 

 embraced in this report. 



SALINITY OF THE WATER. 



The salinity of the water exhibited a very considerable range 

 within the limits covered by the survey. From June 18 to July 10 

 observations were made three times daily at the anchorage of the 

 Fish Hawk and several times each day on the oyster beds undergoing 

 examination. Most of the observations on the Fish Hawk were made 

 at a point about 1 niile south of the east line and about 3 miles 

 offshore, but others, fewer in number, were made near the southern 

 limit of the planted beds, near the middle of the north and south 

 extent of the public beds, and at the upper limit of oyster growth 

 opposite Woodland Beach. 



The data obtained are shown in the following table: 



Salinity of Water Over Oyster Beds, June 18 to July 10. 



Locality. 



Opposite Woodland Beach 



Midway between Ship John and Elbow Light- 

 house 



3| miles southeast by east of Mahon River 

 Light 



6 miles east-northeast of Bowers Beach . . .' 



Number 

 of obser- 

 vations. 



Specific gravity of water corrected. 



Maximum. Minimum. Average 



1.0074 

 1.012] 



1.0149 



1.0178 



1.0032 

 1.0100 



1.0103 

 1.0158 



1.0057 



1.0107 



1.0136 



1.0164 



Average 

 tempera- 

 ture of 

 water. 



