EVIDENCE OF DEEP HABITAT 321 



because it is often difficult to say into which category 

 any particular fish properly falls, and we believe that 

 many fishes have been described as " inhabitants of 

 the greatest depths " upon very insufficient evidence. 



It is obvious that a trawl or dredge fished on the 

 bottom at a depth of, say, 2,000 fathoms, and drawn 

 open to the surface may, and probably often does, 

 capture fishes in the course of its ascent. It must 

 therefore be remembered that the presence of a fish in 

 any net hauled open to the surface proves no more than 

 that such fish was not captured at a greater depth than 

 the lowest point touched by the net. 



There are, of course, many cases in which sufficient 

 evidence is forthcoming of the nature of the habitat 

 of a particular species, especially in the case of those 

 whose normal habitat is in water of not more than 500 

 or 600 fathoms depth. Such evidence may be based 

 upon a shape unsuited for pelagic life (as in a flat fish), 

 or for life at the bottom (as in Argyropelecus), as the case 

 may be ; or, again, by constant captures in surface nets 

 or by some instrument such as a long line, which is not 

 well adapted to taking fishes in the course of its descent 

 or ascent. The constant presence in considerable 

 numbers of any fish in trawls fished at about the same 

 depth raises a strong presumption that such fish has 

 been captured in the ordinary course of fishing on the 

 bottom ; and the presence in a fish's belly of bottom- 

 living organisms points also to a normal habitat on 

 the bottom. Thus we may fairly presume that most 

 deep-sea Gadoids, Macrurids, and Scorpaenoids are 

 bottom fishes, and that the majority of known Stomi- 

 atids and Scopelids do not normally live on the bottom. 



Evidence that a fish does not live on the bottom is, 

 however, no evidence whatever of the precise depth at 

 which it does live. Captures in nets fished in the super - 



21 



