Page:Popular Science Monthly Volume 20.djvu/44

34 destruction of the mature oysters or the non-production of the young is accomplished by means that are harmful only to those individuals directly affected, a cause for the diminution is discovered in harmony with the existing facts.

Considering first the destruction of young, large numbers, immense when compared with the production of the higher orders of animals, are annually destroyed by the falling of the "spat" upon unfavorable ground, the prevalence of heavy freshets which would drive the brood into the bay and probably cause its loss, the ravages of various enemies, and unusual changes of the temperature and density of the water. But all these causes have been in operation continually since the first discovery of the beds, and the animals have survived and increased while contending with them. Therefore, some increase of power must be assigned to one or all of these causes, in order to account for the diminished number of oysters, and there is no reason to suppose that there has been such increase. Thus, by reviewing all the natural causes which affect the beds, we can assign to none of them the destruction of either young or old oysters, or the extension of the beds which has been coincident with the diminution of the number of animals. Remaining, then, as the only other operating cause, is the agency of man.

The oyster-fishery in these localities is carried on in two ways, either by "tonging" or "dredging." The first method, being confined to small areas and to a limited number of fishermen, and susceptible of use but in shoal water, need not be considered. The second method of taking the oysters is as follows: the implement used is called a dredge, or scrape, and resembles a large iron claw, the nails representing the teeth of the dredge. To the back of this claw, or the dredge, is fastened a bag of iron mesh-work, large enough to hold two or three bushels. When the dredge is dragged along the bottom the teeth or claws dig up the oysters and shells, which pass between them and into the network behind. The action is somewhat like that of a harrow. The dredges vary greatly in size, being from two to five feet across the mouth, and of greater or less weight, according to the depth of water in which it is intended to use them. The dredging-vessels vary in size from five to thirty tons, and all use two dredges. When on the oyster-ground the dredges are dropped one from each side, and a sufficient amount of line paid out to insure the "taking" of the teeth; the vessel is then kept under easy sail and at a moderate speed until the dredges are full, that being indicated by the strain on the dredging-line and by other signs known to the fishermen. The instrument is then hauled in by means of a small winch, the contents emptied on the deck, and the dredge put over again. This is continued until the vessel is near the edge of the bed, when the dredges are recovered, the vessel put about, and the dredging resumed in an opposite course. While the dredges are in the water, the mud, sand, sponge, grass, or other débris brought up arc separated from the oysters, and,