DETERIORATION OF AMERICAN OYSTER-BEDS. 37 



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 debris 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 ex- 

 istence, 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 ex- 

 amined, 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 stand- 

 ard, 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 re- 

 maining 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 re- 

 main after its passage, and hence the number of old empty shells 

 should be greater upon a bed that has been dredged than upon one 



