RACES OF SALMON AND PARENT STREAM THEORY. 49 



Races of Salmon and Parent Stream Theory. 



For many years it was believed to be an absolute fact that salmon invariably return 

 to breed in the rivers in which they were born. Concerning this subject, Day (1887, 

 p. 66) says : 'Salmon appear to possess a homing instinct which induces them to return 

 to the river where they were originally reared.' But he says there are instances oc- 

 casionally brought to notice where such could not be the case, mentioning the fact that 

 there are almost yearlj^ reports of a grilse or of a salmon being captured off the mouth 

 of the Thames, or Medwaj^, sometimes even attempting to ascend, but from which 

 localities all these fish have long since been destroyed; consequently they could not be 

 descended from eggs hatched in those rivers. In further evidence that the 'homing 

 instinct' could not be so strongly developed that every fish returned to the locality of its 

 birth. Day said that if it were so, attempts to restock salmon rivers, from distant sources, 

 would be useless, but that experiments have demonstrated such procedure to be almost 

 invariably satisfactory. 



On the other hand, Gouraud (1902, p. 411) writes that, 'The thraldom of an inherited 

 instinct of direction would go far toward explaining the failure of every attempt to 

 elsewhere establish the quinnat or king salmon of the Pacific' by introduction into 

 streams of the Atlantic Coast of the United States, as well as streams of various foreign 

 countries. 'The Pacific salmon,' he says, 'in habit, in strength, and capacity, is so 

 nearly identified with its Atlantic congener that each should readily thrive in the 

 waters of the other.' 



Further on he says : 'Not unUkely the Atlantic salmon possess an inherited cognizance 

 of like oceanic feeding grounds that may be hundreds of miles distant from their native 

 streams; but which would manifestly be unattainable save by fish inheriting an asso- 

 ciated instinct of direction.' Gouraud's examples in support of his ingenious argument 

 are apt, but his entire theory is based upon premises which, if not false, are to some 

 extent incorrect and to a large extent uncertain assumptions. Mr. Gouraud's article 

 is referred to here because it is one of the few attempts at an explanation of salmon 

 movements, and while the explanation is in several ways erroneous, it directs attention 

 to the fact that there are doubtless differences of conditions of environment, habits, and 

 instincts among the various species which, when known, will account for the failures of 

 transplanting. That his explanation does not apply in all cases is evidenced by the fact 

 that, although the king salmon has not been established in Atlantic waters, the hump- 

 back salmon has to the extent that adult fish appear in streams of Maine in which the 

 young of the species were planted. 



Gouraud properly coordinates the feeding and breeding instincts, for they are insepa- 

 rable, paramount, and the most vital of instincts. They are, however, impelling, not 

 directive. As has been previously indicated, the direction of both feeding and breeding 

 movements is a response to external stimuli. It maj^ be the absence of one or another or 

 all of these stimuli, in other words unsuitable environmental conditions, which accounts 

 for failure to estabhsh the king salmon in Atlantic waters and Atlantic salmon in some 

 Atlantic and foreign waters. 



