58 



THE MIGRATION AND CONSERVATION OP SALMON 



of intermingling of populations from the 

 various rivers is necessarily also unknown 

 but whatever the situation in this respect 

 may be, the evidence to date indicates a pre- 

 ponderant return to the natal stream. 



Information concerning the migrations of 

 pink salmon is in close agreement with that 

 for sockeye. Marking experiments have 

 demonstrated a return to the natal stream 

 for the most part. Some wandering was dis- 

 covered but the amount so far revealed is 

 insignificant. 



As to the factors involved in the dispersal 

 of Pacific salmon from the rivers and the 

 migration to the spawning areas, little is 

 known. It is generally believed that tem- 

 perature, salinity and current may be im- 

 portant factors. A preliminary experiment 

 in which the olfactory nerves of sockeye sal- 

 mon were severed did not indicate a signifi- 

 cant amount of wandering. 



It is only reasonable to expect that fish 

 which remain near the mouths of their natal 

 streams naturally enter them at maturity. 

 On the other hand, the British Columbia 

 data do not lead one to the opposite extreme 

 conclusion, namely, that fish which pass be- 

 yond the natal river influence become lost 

 and do not return. Since the results of the 

 tagging of salmon along the British Colum- 

 bia coast show a southeastward movement 

 for the most part and over long distances 

 in many cases, and since a definite return 

 to the natal stream has been demonstrated, 

 it may be logically concluded that there is 

 a northwestward movement of the young 

 fish. That these young fish may pass far 

 beyond the influence of the natal stream 

 seems certain. That they return to the 

 natal stream seems equally certain. What 

 physiological changes associated with the 

 approach of sexual maturity and what cyclic 

 changes in oeeanographic conditions com- 

 bine to bring about this return are as yet 

 unknown. What sensory or guiding mecha- 

 nisms lead the Pacific salmon back to their 

 natal streams are undiscovered. Only a few 

 definite facts concerning the gross features 

 of the migrations are now available and only 

 the patient weaving together of the results 

 of detailed and direct investigations will 

 lead to the solution of the problem. 



Importance op Knov^tledge op Migration 

 TO Conservation 



The tagging programs have indicated 

 certain migration routes for the various 

 species of Pacific salmon. This information 

 has been of value to the administrative of- 

 ficers in the preparation of fishery regula- 

 tions and it has demonstrated in many cases 

 the need for international cooperation in 

 devising conservation measures. 



The marking programs so far have shown 

 very definite returns of marked spring, pink 

 and sockeye salmon to their natal streams. 

 Future investigations may conceivably indi- 

 cate less stability of return but until such 

 time regulations for the species should be 

 made upon the basis of^-the distinctness of 

 the populations of the various river systems. 



Summary 



1. Two methods have been used to trace 

 the migration of salmon in British Colum- 

 bia. The first is tagging in which a serially- 

 i^umbered aluminum strap tag is affixed to 

 the caudal peduncle of the fish. This differ- 

 entiates each individual fish. The second 

 is marking in which fins are removed from 

 fry, fingerlings or yearlings, thus ensuring 

 group identification later. 



2. Tagging has shown that spring salmon 

 may travel long distances in a southeasterly 

 direction before entering the streams to 

 spawn. In so doing they may cross interna- 

 tional boundaries and are subject to capture 

 at many points. A higher percentage of 

 tagged spring salmon reach the Columbia 

 River from the west coast of Vancouver 

 Island than from the west coast of the Queen 

 Charlotte Islands. These facts together 

 with knowledge of the return of the species 

 to the natal Columbia as demonstrated by 

 marking experiments, seem sufficient cir- 

 cumstantial evidence to suppose a north- 

 westerly feeding migration and a southeast- 

 erly spawning journey for the species. 



3. Sockeye salmon marking experiments 

 have demonstrated a preponderant return 

 to the natal streams. Examination of large 

 series of scales from the four main rivet 

 systems have indicated from the scale pat- 



