PACIFIC SALMON 



69 



Tagging Adult Salmon in Salt 

 Water 



Experiments in tagging adult salmon at 

 feeding grounds or returning to spawn have 

 been carried out for some years under the 

 auspices of the U. S. Bureau of Fisheries 

 and in Canada. The first were by William- 

 son, and by others under the direction of 

 Rich. More recently they have been con- 

 tinued by Davidson whose papers include 

 a summary of the earlier work. This work 

 indicates clearly definite lines of movement 

 followed by adults returning from oceanic 

 feeding grounds. They also give some evi- 

 dence on definite times of migration for 

 different groups of fish. The percentage of 

 tagged fish recovered was large enough, 

 especially in later experiments, to determine 

 both routes and time ; they show almost the 

 same definiteness for the migration route as 

 is necessarily involved in fresh water move- 

 ments. Davidson made in one place the 

 significant observation that with a south- 

 east wind one course is followed in the main 

 but **if a southwest wind is blowing the 

 opposite course is more apt to be taken." 

 Since wind direction certainly modifies 

 locally water movements, Davidson's obser- 

 vations evidently suggest current influence 

 on movements of the salmon. 



The work done by Williamson (1927: 

 305) led him to the following conclusion: 

 "The result of the tagging experiment is 

 encouraging, but as in most similar investi- 

 gations there is a larger proportion of the 

 tagged fishes of which no trace has been 

 found. The sockeye returns are the largest 

 and it is significant that 20 per cent were 

 recaptured in each experiment. Most of 

 these were found in or in the vicinity of 

 rivers which they were entering to spawn. 

 But what of the remaining 80 per cent?" 

 [Italics mine.] Williamson's query has 

 never been answered and so far as I have 

 been able to find no intensive search has been 

 made for the missing 80 per cent. In David- 

 son 's last paper he states that "the majority 

 of the adults return to spawn in the streams 

 of their origin" (1938: 644), but in the 

 tables given in that same paper one may 



read the following summaries regarding the 

 most successful catches recorded : Recov- 

 eries of different dates — At Cape Fox, 26 to 

 376 fish at one point, total 1,159 fish con- 

 stituting from 19 per cent of those tagged at 

 one point to 29 per cent of all adults tagged. 

 At Cape Chason 10 to 373 fish recovered 

 at one point in a total' of 968 constituting 

 from 23 to 42 per cent of those tagged at 

 one point or only 25 per cent of the total 

 tagged. At McLean Point the total of 998 

 recovered was highest, forming 41 per cent 

 of all fish tagged. At other points the record 

 shows that lesser percentages of those tagged 

 were recovered later. These figures demon- 

 strate that in Davidson's experiments the 

 proportion missing was smaller than in 

 Williamson's. But those not accounted for 

 still constitute 60 per cent or more of the 

 numbers tagged. 



These experiments appear to give no sig- 

 nificant evidence on the question at issue in 

 the discussion of the parent-stream theory, 

 although often cited to establish its verity. 

 The origin of the salmon tagged was not 

 known, and hence their ultimate destination 

 was not the parent stream except by assump- 

 tion. Both authors state that only a few 

 tagged fish were recovered on spawning 

 grounds and neither states whether that 

 number was obtained in a single spawning 

 area though Davidson remarks frankly "it 

 is not improbable that salmon occasionally 

 stray from their normal course of migra- 

 tion." The extent and character of that 

 departure from the assumed uniformity is 

 precisely the question at issue. These experi- 

 ments are of high value in tracing the pre- 

 cise migration routes, and it is to be hoped 

 that they may be continued and extended. 



Davidson's paper contains another sug- 

 gestive finding. His final conclusion reads 

 thus : * ' Again we find a seasonal difference 

 in distribution. The early migrants are 

 destined for the localities remote from the 

 sea, the later migrants for the more proxi- 

 mate localities. ' ' One may well ask whether 

 all the fish in one population group return 

 at the same time to reach under fixed envir- 

 onmental conditions one area in fresh water 

 or whether the fact that environmental con- 



