PACIFIC SALMON 



47 



tion and so cannot be ascribed to differences 

 in the length of time elapsed after leaving 

 the feeding grounds ; small but statistically- 

 significant differences exist in respect of 

 such characters as proportional measure- 

 ments and counts of vertebrae, fin rays, etc. 

 Of a somewhat different nature are the dif- 

 ferences observed in the scale markings 

 which, in effect, provide a permanent and 

 continuous record of the rate of groMi:h 

 throughout the life of the fish. 



2. What I have chosen to call the statis- 

 tical evidences of local populations include 

 the persistence over long periods of time of 

 distinctive age group ratios (as determined 

 from scale examinations) and of distinctive 

 cycles of abundance. The two are often 

 related especially in cases, as that of the 

 famous Fraser River sockeye run, in which 

 the size of the breeding population is the 

 chief determinant of future abundance. 

 Such distinctive cycles of abundance have 

 been demonstrated with statistical signifi- 

 cance for a number of Alaskan streams and 

 for at least two species, the red and pink 

 salmon (0. nerka and 0. gorhuscha) . 



3. Experimental evidence of local popu- 

 lations of Pacific salmon rests chiefly upon 

 the results of numerous large marking ex- 

 periments involving an aggregate of some 

 three or four million young salmon. These 

 have been marked by clipping fins before 

 or during the seaward migration and the 

 adults were recovered from the commercial 

 fisheries or from the spawning areas. I 

 started a series of such experiments on the 

 Columbia River in 1916 and since then 

 hardly a year has passed in which additional 

 experiments have not been started. Most of 

 these have had to do with the Chinook sal- 

 mon (0. tschawytscha) and the sockeye or 

 blueback (0. nerka). The results have 

 shown beyond any reasonable doubt that the 

 marked fish return in overwhelming propor- 

 tions to the stream and even to the tributary 

 in which they spent the early part of their 

 existence. Aside from the evidence indicat- 

 ing the return of the adults to their home 

 streams these experiments have provided 

 evidence on a number of other problems that 

 do not bear so directly upon the main sub- 



ject of this discussion. Other evidence, ex- 

 perimental in nature, is that provided by the 

 establishment of salmon runs in streams 

 where no runs previously existed; as in the 

 case of the Chinook salmon run into Spring 

 Creek and that of the red salmon runs that 

 were maintained for a number of years in 

 Herman and Tanner Creeks, all in the 

 Columbia River basin; similarly the grad- 

 ual rehabilitation of depleted runs when 

 properly protected over a period of years. 

 The mere fact that the run of one stream 

 may be depleted by too intensive exploita- 

 tion while that of a neighboring stream is 

 not is strong evidence in favor of the exis- 

 tence of local populations. Such a case is 

 presented by the maintenance of a good run 

 of red salmon into the Karluk River on Ko- 

 diak Island while the runs into Red River, 

 Uganik River and Little River were being 

 depleted to the point of commercial exhaus- 

 tion. 



To summarize : Diverse evidence points so 

 clearly to the existence of local, self -perpetu- 

 ating populations in the Pacific salmon that 

 any hypotheses that do not conform must 

 be subject to considerable doubt. This, I 

 believe, must be accepted as a proved fact 

 regardless of what may or may not be dis- 

 covered about the extent of the oceanic mi- 

 grations, regardless of how the migrations 

 and particularly the return to the home 

 stream may be accomplished and regardless 

 of the reasons why the movements are made. 

 Practical conservation measures must be 

 based upon the acceptance of the ''home 

 stream theory" as an essentially correct 

 statement. 



Turning now to consider the nature and 

 extent of the migrations: The general fea- 

 tures of the migrations of the Pacific sal- 

 mons are well known and are summarized 

 in the mere statement that these are ana- 

 dromous fishes. The details of the seaward 

 migration as to time, rate of travel, age of 

 the fish and so on, have been, and still are, 

 under investigation but are not of particu- 

 lar concern at this time. The details of the 

 oceanic migrations, however, are of major 

 importance both on account of their bearing 

 on certain interesting problems in animal 



