Page:Popular Science Monthly Volume 20.djvu/48

38 that has not; and, if that number is very large, it shows that the population of the bed has been destroyed. Upon an unworked bed the number of old shells will show approximately the number of oysters perishing from natural causes; and, should the number on any worked bed exceed this on the undredged one, it may be concluded that Nature is being assisted in her work of destruction.

The quantity of matter brought up in the dredge was measured in all cases during the season of 1879, as was also the quantity of oysters and of débris. On the unworked beds in the bay this débris was found to equal thirty per cent, of the whole amount of matter brought up. On nearly every bed in the sounds the percentage of débris was greater than that on the unworked beds, and in Pocomoke Sound it was extraordinarily large, amounting in some of the beds to as much as ninety-seven per cent.!

During the season of 1878 a method was devised by which the number of oysters to the square yard could be determined approximately; and, though this number was not near the true one, yet, as the measurements were always made in the same manner, it was useful as affording a standard for comparing the results of subsequent seasons or of different localities.

The number of oysters to the square yard obtained by this method depended mainly upon the number of oysters brought up by the dredge; and, as already explained, the difficulty of obtaining the animals was much greater on the new and unworked beds than upon those which had been dredged for many years; therefore, the number to the square yard, other things being equal, should be much greater on the old beds than upon those recently discovered. To make this plainer, a very simple illustration will suffice: Any person knows that the plowing or harrowing of a field frequently subjected to that process is much easier than the breaking up of entirely new ground, and the dredging of an oyster-bed is very similar to the harrowing of a field.

The number of oysters to the square yard, as shown by the method used, should then be greater upon the old beds than upon the new, and, comparing the results of successive seasons on the same bed, if it is found that the number of oysters to the square yard is decreasing, it may be concluded that too large a number of the animals is annually removed. The investigation of the beds in 1879 showed that on sixty per cent, of the beds in Tangier Sound there was a decrease in the number of oysters during the season of 1878-'79, and that on sixty per cent, of the beds the number of oysters to the square yard was less than on the newly discovered beds in the bay, and in no case was the number much greater. In Pocomoke Sound, on every bed the number of oysters to the square yard was considerably less than in 1878, and also much below the number on the new beds in the bay.

On several of the beds in the sounds the ratio of young growth to