l62 BULLETIN OF THE BUREAU OF FISHERIES. 



There is no evidence whatever for distribution in accordance with temperature 

 within the narrow Hmits of the present region. Most of the species taken in the dredge 

 are ones which have a more or less extended northerly as well as southerly range along 

 the coast, and it so happens that Pholis gunnelus, the only strictly northern species 

 which was dredged with any frequency, was taken at scattered stations throughout 

 most of the Sound, but was not recorded from its western end. It is quite likely that 

 the local distribution of this fish is limited by the character of the bottom (by preference 

 stony) and by the occurrence of certain r-lgae. Those fishes which are recorded with 

 greatest frequency at the western end of the Sound are mainly species of flounders and 

 skates, which occur predominantly on sandy bottoms. Of the five species thus restricted 

 (Raja erinacca, Lophopsetta maculata, Paralichthys ohlongus, and, to a less extent, Para- 

 lichthys dentatus and P seudoplcuronectcs americanus) , two are predominantly southward 

 ranging, while the other three have ranges which extend about equally in both directions. 

 Thus the character of the bottom in this western area of Vineyard Sound is doubtless 

 responsible directly or indirectly for the distribution of these fishes. The case is quite 

 different from that of many other organisms which have been considered by us, whose 

 presence near the open end of the Sound is to be explained by reference to the lower 

 water temperature which obtains there. 



Even if we had a full and accurate knowledge of the local distribution of these 

 various fishes, we should hardly expect to find the same dependence upon temperature 

 conditions as was found in the case of some other organisms. Since fishes are free to 

 move from place to place according to their needs, they are not subject to the constant 

 influence of any set of conditions acting throughout the entire life cycle, as is the case 

 with fixed or slowly moving organisms. It may well be (see pp. 175-177) that the restrict- 

 ing effects of a colder or warmer environment in relation to distribution depend in many 

 instances upon its action during the reproductive period alone, and that the adult 

 organism itself might be able to thrive under conditions unfavorable to its early develop- 

 ment or to its reproductive activity. Indeed it is likely that such a possibility is often 

 realized in the case of animals having sufficient powers of locomotion. And it is perhaps 

 among the fishes themselves, many of which migrate to warmer waters for the purposes 

 of reproduction, that the best examples may be found. 



The distribution of most fishes within the narrow limits of such a region as the pres- 

 ent one is doubtless determined chiefly by the occurrence of their food supply. This we 

 may say with a high degree of probability, although we may not be able to determine 

 many definite cases of correlation between the occurrence of particular species of fishes 

 and the particular organisms which serve as their food. In the case of such predom- 

 inantly bottom dwelling species as the flounders and the skates, it seems very probable 

 that the character of the bottom is an independent factor in determining distribution. 

 Such fishes require beds of comparatively clear sand, upon which they rest or under 

 which they may find concealment. 



