Page:Popular Science Monthly Volume 20.djvu/47

Rh soft and easily penetrated. The dredge took the oysters readily, and without great effort. There was much mud among the oysters, and the amount of old broken shells and other débris was quite large. It is evident that in any community there must be in the life of a given generation a depletion of number in each successive stage of existence, or, in other words, as the age of the generation increases, the number of individuals decreases. Therefore, on an oyster-bed we should have a larger number of young than mature oysters, provided that we include as "young" the offspring of a sufficient number of spawning-seasons to guard against irregular production in any one season; and, if, having taken that precaution, we find the number of mature oysters to exceed the number of young growth, we may safely decide that there is a deficient production due to some cause, natural or otherwise.

On a natural bed which has not been worked, and which has had no abnormal conditions to contend with, the number of young oysters should, then, exceed the number of those mature. Let us see if this was actually the case on the unworked beds in Chesapeake Bay.

All the oysters examined during the season of 1879 were measured and distributed into four classes. The first two classes comprised the mature oysters; the last two, the young growth. During the season several areas which had never been dredged over were carefully examined, with the following result: Over twenty thousand oysters were measured and classified, and the ratio of young growth to mature oysters was found to be as three to two, or one and five tenths of the former class to one of the latter. This ratio was accepted as a standard, and the ratios of young oysters to mature on all the beds in the sounds were compared with it separately and collectively. Over one hundred thousand oysters were taken from those beds, measured and classified in a similar manner to that adopted for the oysters from the beds in the bay, and the ratio of young growth to mature oysters was found to be as three to six, or five tenths of the former class to one of the latter. Thus, on the new beds the young growth outnumbered the mature, while on the worked beds in the sounds the mature oysters outnumbered the young growth.

The action of the dredge is very destructive to the oysters remaining on the bed. They are not only roughly detached from each other and from the different objects to which they cling, but are, no doubt, frequently left in such positions as will prevent the opening of the valves without allowing the entrance of mud or sand, and thus insuring destruction. The teeth of the dredge also break the lips of the valves, and thus prevent their complete closure, which is the only defense of the oyster against its numerous enemies. Thus, the dredge causes the destruction indirectly of a large number of oysters that remain after its passage, and hence the number of old empty shells should be greater upon a bed that has been dredged than upon one