CH. l] THE EXPLORATION OF THE SEA 23 



the trawl is modified, and instead of the instrument described in 

 this chapter a trawl frame is employed which fishes equally well 

 no matter on which side it reaches the bottom, an important con- 

 sideration, since it is exceedingly difficult so to manipulate a trawl 

 in deep water that it reaches the bottom on one particular side. 



Fig. 10. The so-called " Agassiz trawl." 



Success in trawling, even in shallow water, depends on a 

 variety of circumstances, such as the length of line used, the exact 

 construction and trim of the apparatus, the speed of the vessel, &c. 

 Even with the same apparatus fishermen of different degrees of 

 experience and skill obtain very variable results on ground which 

 might reasonably be expected to give uniform results, a considera- 

 tion which does not receive due attention in discussions of trawling 

 results applied to the elucidation of the abundance of fishes or 

 other organisms on a sea area from time to time. 



In fishing with a trawl net we catch whatever is upon the sea 

 floor, except of course such animals which are able to swim out of 

 the trawl when once they have been caught in it. Then the net 

 usually catches a larger or smaller mass of bottom invertebrates, 

 weed, sand and mud, stones, &c. When the catch is unusually 

 large and the net is hauled for a long time many of the more 

 delicate organisms are injured or killed by the pressure of the other 

 materials in the catch, although this destructive action of the trawl 

 is far less than one might imagine on a first consideration of its 

 mode of action. When it is desired to obtain organisms which the 

 trawl might injure fishing baskets are sometimes employed, a 

 method of scientific fishing which was first systematically adopted 

 by the Prince of Monaco ^ though it is really only a modification 

 of the primitive lobster basket or creel. The fishing basket or 

 "Nasse" is a frame of wood or iron which may have various forms : 

 that employed by the Prince of Monaco was a short triangular 

 prism. It is covered with netting and in this are openings of 

 various sizes, or there may be inserted baskets of different sizes of 



^ Richard, Les Campagnes Scientifiques, Monaco, 1900. 



