Page:Popular Science Monthly Volume 20.djvu/43

Rh bed, a new factor must be brought into operation, when, all conditions being changed, the life of the animals begins anew and progresses differently.

As already stated, the character of both beds and oysters in the locality under consideration has undergone great changes during the last thirty years, and the causes for those changes must be sought among such as it is known would produce like effects. Disregarding for the present the agency of man in the matter, the question is, What natural cause or causes would both expand the beds and diminish the number of oysters?

A bed is extended, naturally, by the drifting "spat" or young brood attaching themselves to any appropriate "cultch" contiguous to the bed. This manner of extending the area is much assisted by the current, and consequently natural extension is greatest in the direction of the currents. The principal expansion of the beds, so far as could be effected by Nature, must, however, have been accomplished long ago, for as far back as can be remembered the beds have been surrounded by soft bottoms of a character most destructive to the young brood. Unless, then, some substance is interposed between this soft bottom and the drifting "spat," they will sink into it and be destroyed. Nature has no means of offering such a substance except to a very small extent, and consequently the great expansion of the beds could not have been the result of natural causes, but must be assigned to other agents.

The diminution of the number of oysters might have been effected by several natural causes. An increased deposit of earthy or vegetable matter upon the beds would, if in sufficient quantities to bury the oyster, effect the destruction of old and young. No such deposit has been noticed, nor could it well occur without showing its presence in other ways, principally by changing the channels and causing shoals, but no such changes have occurred; the deviations in channels, shoals, and character of bottom, from those established by the first hydrographic survey of the locality, being very slight indeed.

A change in the character of the water and bottom which would probably follow a change of channel, and possibly occur without such change, might, by depriving the animals of their proper food, cause their deterioration and destruction; but such a change, though it would certainly diminish the number of oysters, would do so suddenly, and the evil effects would be noticed in the oysters remaining, their quality, flavor, and vitality being very much impaired. No such impairment has been observed, however, the animals being at present much larger and finer than when the beds were first discovered.

That fact alone will eliminate many quantities from the equation, for any natural cause injurious to all the oysters on a bed would show its effects upon those remaining, and an examination of a few specimens would be sufficient to determine the question. If, however, the