42 KENDALL: NEW ENGLAND SALMONS. 



'4. Diminishing specific gravity consequent upon increasing fatness probably con- 

 stitutes a strong directive influence governing the movements of fishes, both marine and 

 anadromous.' 



Specific gravity would thus tend to bring the fish to the surface and if thereby it comes 

 in contact with fresh water it would, as Roule says, follow it up. For salmon far from 

 shore, to find the fresh-water factor, some other vis a tergo is required to force it toward 

 the fresh water. Furthermore Taylor seems satisfied to have got his fish into the fresh 

 water and does not explain how it is that the salmon is able 'to float' in fresh water 

 after its specific gravity is increased through the reproductive changes. 



Yet, it is not impossible that the seasonal food of the salmon such as smelt, capelin, 

 herring, sand eels, etc., may concentrate in those regions where the salmon may come in 

 contact with the requisite stimuli. In fact we have already cited instances of marine 

 food being found in the stomachs of salmon after they had entered the river. There are 

 also known instances of salmon pursuing smelts and young herring well up in the 

 mouths of the rivers. There is also considerable evidence that salmon do not habituaUy 

 go far enough away from shore to entirely avoid fresh water, at least at the surface and 

 at certain seasons. 



After making other comparisons and statements concerning characters of streams 

 referred to, Calderwood (1907, p. 133) concludes from the facts that the theory that 

 salmon enter rivers warmer than the sea is erroneous and that temperature has nothing 

 to do with the seasonable character of the river in Scotland, in so far as the actual en- 

 trance of salmon from the sea is concerned. But he goes on to say that after a fish has 

 once entered the mouth of a river fluctuations of temperature exercise a distinct in- 

 fluence, but in making an early or late river temperature does not appear to play a part. 



This latter conclusion is probably quite true so far as warmer river water is concerned 

 but it has not been shown that when salmon enter a river its water is not colder than the 

 immediate sea at the time of entrance. It is natural to assume that in summer river 

 water is necessarily warmer than the sea into which it flows. But there appears to be no 

 evidence that the time of entrance is not during one of those 'fluctuations' when the river 

 is relatively colder than the immediate sea water, as it has been shown that various 

 streams differ more or less from each other in character and time of salmon runs, and 

 that the same river sometimes varies in those respects according to the season or con- 

 dition therein. Neither Gurley's nor Roule's theory predicates definite degrees of 

 difference of temperature affecting salmon runs, but that the runs are related to cooler 

 water in the one theory and to greater oxygen content in the other. But, as has been 

 stated, the one involves the other. 



In this connection the conclusions reached by Nordquist (1924, p. 5-6) may be con- 

 sidered. In his studies of the salmon rivers of Finland, Nordquist had previously come 

 to the conclusion that the time of the breaking up of the ice, temperature of the water, 

 and direction of the wind had no direct connection with the time of entering of salmon 

 into the rivers, but that the water level in the river did have an influence in that direction. 



After presenting other rivers in evidence that it is the volume of water rather than 



