6 



2 ANNALES DE L'INSTITUT OCÉANOGRAPHIQUE. 



ing the oysters, which are always lying on the bottom, and of passing over much that is 

 not wanted. Nevertheless it is a fact, ascertained by divers in the Limfjord, that the 

 dredge does not capture all the oysters on its way, but only a comparatively small percen- 

 tage of them, larger or smaller according to the nature of the bottom. Thus, it does not 

 give a correct idea of the true number of oysters on the bottom ; this is only obtained by 

 means of divers. As technical Adviser to the Danish Government I have had such diving 

 experiments carried out on a large scale. 



Naturalists have modified this dredge in many ways, for example by giving the bag 

 small meshes so that it can also take small animals ; but the result is, that it is quickly 

 filled and loses its fishing capacity ; on soft clay bottom it may be filled after having been 

 dragged ^ — i meter through it, on hard sandy bottom it may skim the bottom for a long 

 time but it then only exceptionally catches the animals living in the bottom-soil, mainly 

 taking the animals lying on the bottom such as large Gastropods, certain Echinids or 

 Asterids, etc., while the large digging Lamellibranchs or Annelids are only quite excep- 

 tionally captured. It thus gives quite a false representation of the animal life of the sea- 

 bottom, for it catches some species better than others and gives no information at all 

 about the quantity of animals on each m 2 (partly because it is generally not known how 

 long the dredge has been dragged along the bottom, partly because, even if this could be 

 ascenained, one generally does not know if it has been fishing the whole way); but for 

 collecting a number af animals for systematic, zoological examination the dredge is 

 excellent and has also in this respect been of great scientific importance. 



I shall not dwell here on all the different kinds of dredges that have been con- 

 structed in the course of time, my objections against dredges applies to them all without 

 exception. 



Several of the new fishing apparatus, which the Prince of Monaco, Johan Hjort 

 and I myself have introduced into fishery investigations give much better information, 

 one might almost say, regarding the quantity of many swimming animals, than the dredge 

 does for the bottom animals, and as regards the quantity of the small organisms floating 

 in the water Hensen's plankton nets are of still greater use. Edward Forbes is certainly 

 the one who more than anybody else, made use of the dredge in earlier times, but the 

 vignette found in his and Godwin-Austen's book The Natural History of The European 

 Seas, p. VIII, hardly gives the impression, that he was of opinion that the dredge took 

 everything found on the bottom of the sea. H. Jungersen from the Danish Ingolf Expe- 

 dition has compared a dredging ship with an air-ship towing a dredge over Copenhagen, 

 catching a policeman in one street and a perambulator in another, and from this we draw 

 conclusions as to the whole population of the town. It is time, therefore, to look for 

 other apparatus, which together with the dredge may give better information regarding 

 the quantity of animals living on the bottom of the sea and throw some light upon the true 

 quantitative relations among the different species. 



Such apparatus has been constructed and used by me for several years (i) in the Danish 



(i) Ann. Report Dan. Biol. Station, XX, 1912. Valuation of the Sea. I, 



