70 



THE MIGRATION AND CONSERVATION OF SALMON 



ditions in fresh water, changing as has been 

 shown in current, temperature and other 

 factors with advancing seasons, do not condi- 

 tion the return of fish in one month to one 

 region in the stream and in another season 

 to another stream or to a different part of 

 the same stream. Indeed seasonal variation 

 in currents alongshore which are well recog- 

 nized locally in salt waters, may play an 

 important part in the sorting of fish as 

 found by Davidson and shown in his con- 

 clusion just quoted. 



Studies on Pacific salmon furnish in- 

 stances from particular places or years which 

 deserve special mention in this discussion. 

 As an example may be cited the following 

 account from Rich and Ball (1931 : 670) on 

 the run of pink salmon at Karluk: ** Es- 

 capement of pinks [at Karluk] in 1924 was 

 tremendous ... a conservative estimate 

 ... in excess of 4,000,000. All entered lat- 

 ter half of July and in August. . . . Decay- 

 ing bodies so polluted the water that nothing 

 could remain in the stream and survive. . . . 

 Beach for miles covered by remarkable ag- 

 gregation of salmon bones." This occur- 

 rence can apparently not be explained on the 

 basis of a " homing instinct. ' ' It may easily 

 be seen as the results of some unexpected 

 shift in local currents or temperature in the 

 sea. Such changes are known and recog- 

 nized by fishermen as well as by ocean- 

 ographers. 



Evidence of Environmental Control 



Long continued observations on the ac- 

 tivities of Pacific salmon during the period 

 of fresh water migration has yielded some 

 definite information regarding specific fac- 

 tors which appear to exercise control over the 

 movements of the fish during that period. 

 The situation is far less complex than that 

 offered by the ocean migration, the factors 

 more narrowly limited, less variable and 

 more easily observed and measured while at 

 the same time the fish are more readily 

 seen and followed. Furthermore conditions 

 are in part at least subject to control and 

 modification so that while in fresh water 

 continued observation of small groups is 

 often feasible, some experimentation is also 



possible, and conclusions may be more read- 

 ily tested. For these and other reasons I 

 decided to confine my own attention to the 

 fresh water migration and further primarily 

 to that of a single species, the red salmon 

 or sockeye (Oncorhynchus nerka). In this 

 way I hoped to avoid confusion incident to 

 combining in a single record activities of 

 separate species which, although manifesting 

 evident relationship, still exhibited constant 

 detailed differences in habit as well as in 

 structure. The results of my studies are 

 contained in papers already published (see 

 literature list at end of this paper) and in 

 others under way. They are not as extensive 

 as one might wish and they have left many 

 questions still unanswered. But in my opin- 

 ion they have disclosed much which can not 

 be reconciled with the conception that some 

 blind instinct forces the returning adults 

 to follow a predetermined path regardless 

 of the changes that time brings about. 



On the Atlantic coast. Huntsman has al- 

 ready shown for Salmo solar the influence 

 of environmental factors on the movements 

 of the fish in salt water. Further studies 

 on the Pacific salmon will no doubt add fur- 

 ther evidence of environmental control in 

 salt water on species of Oncorhynchus. Re- 

 cent work on oceanic canyons and currents 

 along the north Pacific coast have made 

 extensive discoveries of conditions hitherto 

 unknown which are surely of some import 

 in controlling movements of the Pacific 

 salmon during its marine life. 



Summary 



While in the main the phases in the life 

 cycle of the salmon have been established, 

 its migration is still unexplained. Accord- 

 ing to popular view salmon return to the 

 natal stream. The author's studies, pur- 

 posely limited chiefly to the freshwater 

 period and to the single species {Oncorhyn- 

 chus nerka), thus attacked the problem in 

 its simplest form and have led to question- 

 ing the tenability of the home stream as- 

 sumption. Analysis in detail of the records 

 given by previous investigators revealed 

 gaps in the evidence, exceptions to the rule 

 and conditions unexplained by the simple 



