154 ^^^ OYSTER. 



RATIO BETWEEN LIVING OYSTERS AND DEAD SHELLS. 



When the oysters are culled upon the beds where 

 they are caught, the dead shells are thrown back, and 

 the oysters upon a bed which has been overworked 

 will therefore form a smaller part of the total contents 

 of the dredge than they will upon a more prosperous 

 and valuable bed. In a dredge which has been hauled 

 over an unexhausted bed, the living oysters are many 

 and the shells are few, while the dredge brings up 

 from an exhausted bed a great mass of rubbish, which 

 must be lifted and handled in order to obtain a few 

 oysters. 



The ratio between the living oysters and the dead 

 shells therefore furnishes us with a means for deciding 

 whether a bed is deteriorating or not. This method 

 of estimating the condition of the beds is a very rough 

 one, and the evidence is not of much value when only 

 a single bed is examined. The dead shells are swept 

 into the channel in some places, and covered up by 

 sand or mud in others, so that the dredge may come 

 up filled with shells when it happens to strike a bed 

 where they have been swept together, and in another 

 case, where most of the shells are buried, it may con- 

 tain few shells. If the dredge is heavy and is dragged 

 with a long line, it may dig into the mud and become 

 filled with old shells, where another dredge, or the 

 same dredge dragged in a different way, may contain 

 few or none. The contents of the dredge are deter- 

 mined by so many accidents that single observations 

 of the ratio between shells and oysters are of little 

 value, but the case is different where a great number 



