Determination 



of the Quantity of Animal Life on the Sea-bottom, 

 its Communities and their Geographical Importance. 



i (Valuation of the Sea II) 



By C. G. Joh PETERSEN 



Ph. d., L. L. D. 

 Director of the Danish Biological Station. Denmark. 



During many years, since the Danish zoologist O. F. Millier wrote his excellent 

 papers on marine animals, the dredge has been the main implement used by naturalists 

 in their investigations on the animals of the sea-bottom. The fishery investigations of 

 recent years, in the new as well as the old world, have introduced other fishing apparatus 

 specially suited for capturing the quickly swimming animals or the rarer animals lying 

 more scattered on the sea-bottom ; but for the study of the true bottom-animals the 

 dredge has been the only apparatus used, except when at ebbtide the sea-bottom is laid 

 bare; observations can then be made directly on the animals thereof. 



Many different kinds of dredges have been used, square, triangular, crescent-shaped, 

 with or without teeth, large, small, with bags of netting, canvas or wire, but all these 

 forms can only be considered as transformed oyster-dredges, which were indeed the 

 models for O. F. Muller, Marsigli and Donati. 



The object of the oyster-dredge is to capture the greatest quantity of oysters in the 

 shortest possible time; whether it is dragged a shorter or greater distance over the bottom 

 is of no consequence so long as it takes many oysters in a short time. The oyster-fisher 

 does not want his dredge filled with stones or sand, nor with smaller animals and objects 

 from the bottom , everything of this kind that comes into the dredge must go out again 

 as quickly as possible, in order not to fill the bag, which would then fish no more. This 

 is avoided partly by making the frame in such a way, that it does not dig too deep down 

 into the bottom, if possible not at all, partly by making the meshes of the bag so large 

 that many of the smaller objects pass through. The oyster dredge has gradually been sub- 

 jected to many experiments and it is wonderful to see, how it serves its purpose of catch- 

 T. VI. -Fasc. i. i 



