FISHERY BULLETIN: VOL. 71, NO. 3 



heavy predators of young sockeye salmon in 

 Cultus Lake, Roos (pers. comm.) has noted Dolly 

 Vardens preying on sockeye salmon smolts as 

 they leave Chilko Lake. While the normal pro- 

 ductivity of sockeye salmon runs must adjust 

 to this mortality, these losses could become criti- 

 cal in populations subjected to other extraordi- 

 nary pressures. Under such circumstances an 

 objective evaluation of the effects of Dolly Varden 

 and Arctic char on the productivity of different 

 sockeye salmon races in the Karluk system war- 

 rants more attention than it has been accorded 

 so far. 



INTERPRETATION OF 

 DECLINE IN CATCH 



The information recorded above has been 

 developed from observations which have been 

 made almost accidentally. However, the decline 

 in catch is real and it is evident that it must be 

 the result of two factors. The first and major 

 cause has been the fishing out of the middle por- 

 tion of the Karluk run noted by Thompson 

 (1950) and by Thompson and Bevan (1954). 

 This process continued until the 1950's and in 

 the even years it still continues because the pink 

 salmon run must be harvested and this run 

 overlaps the midseason sockeye salmon runs in 

 the Karluk system. This depletion of the 

 midseason Karluk sockeye salmon loins was 

 responsible for the change of the sockeye salmon 

 run from a single mode to one with a mode in 

 June and another in August. It also was one 

 factor which reduced the annual catch of Karluk 

 fish from an average of 3,195,000 fish in 1889-94 

 to an average of 107,000 fish in 1953-58 and to 

 14,000 fish in 1971. 



But, along with this reduction of the most 

 productive segments of the Karluk spawning 

 run, there has been the additional effect since 

 1945 of the weir on both adult and young salmon. 

 The weir, located at the lower end of the Karluk 

 River from 1921 to 1941 might not have affected 

 adults, but after 1945 and in its location just 

 below the lake it must have affected both adults 

 and blocked the migration of fry and fingerling 

 sockeye salmon out of the Karluk River. At any 

 rate, the peak run in 1934 was much smaller 

 than in 1926 (see Rounsefell, 1958, Figure 4). 

 After the weir was moved to the upper end of 



the Karluk River in 1945, however, the size of 

 the Karluk sockeye salmon runs fell more 

 rapidly than before and have finally been re- 

 duced to present minimal size. 



The correspondence between the location of 

 the weir and the drop in productivity is clearly 

 demonstrated in Figure 2 which relates the 

 number of spawners to the number of returns. 

 While the data prior to 1921 are not reliable mea- 

 sures of the size of the total run, they are related 

 to the size of catch and serve to show that in this 

 early period the level of productivity of the Kar- 

 luk run was much greater than it has been since 

 1921. There is also some question as to the accu- 

 racy of age readings (Walker, see footnote 10) 

 but we have used the age readings used before by 

 Rounsefell and the age distributions in data given 

 to us by W. A. Smoker of the Auke Bay Fisheries 

 Laboratory for the years since 1946 as the best 

 information that is available. The level of pro- 

 ductivity shown in Figure 2 since 1945 is but a 

 fraction of the earlier level, and while the data 

 are too widely scattered to provide a reliable 

 basis for calculating a production curve, it is 

 interesting that the maximum of such a curve 

 for 1946 to 1961 inclusive is at 345,000 spawn- 

 ers, which could be expected to return a total of 

 720,000 fish. The curve for 1921 through 1939 

 peaks at 1,050,000 spawners, with a return of 

 1,875,000 fish. Obviously, the earlier level of pro- 

 ductivity is more desirable than the current one 

 which seems to have an ultimate end point of 

 zero. The cui've for the years before 1921 must 

 have been higher still with a correspondingly 

 higher expected return. 



SUMMARY AND DISCUSSION 



It is evident that the spawning of sockeye in 

 the Karluk River has not been observed except 

 incidentally. Rounsefell (1958:168) explains 

 that: 



The extent of spawning in the main river below Kar- 

 luk Lake may not have received as much attention as 

 it may deserve because (1) such spawning often occurred 

 rather late in the season and so was only partially ob- 

 served by summer field parties visiting the lake, (2) since 

 spawning fish would often be intermingled with fish 

 migrating into the lake it was somewhat difficult to dis- 

 tinguish spawners from upstream migrants, and (3) be- 

 cause of the extremely small percentage of mature fish 



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