MATHISEN: NUSHAGAK SOCKEYE SALMON FISHERY 



7.0 



SO- 



SO 



■5 « 



c — 



2.0- 



to 



T3 



1.0- 



0.7 



•5 ""0.5 



!0.3- 



0.2- 



0.1 



I 

 50 



I — I — r- 



55 



Total 



1 — I — I — I — I — r 



60 

 length (cm) 



65 



Figure 6. — Log ratio of catches made in Nusliagak, 1928, 

 by 6- and 5 y2-inch gill nets. Males and females combined 

 by centimeter groups. 



tivity, by a shift to smaller net sizes over the 

 years which reduced the potential egg deposition 

 rather than the numerical size of the escape- 

 ments. Such an explanation would be most ap- 

 propriate for the transfer from the first to the 

 second major period of the Nushagak fishery in 

 1919. But this argument loses some strength 

 when other sockeye salmon systems outside 

 Bristol Bay are considered. 



The given description of the Nushagak fishery 

 and reduction of reproductive rate are almost 

 identical to that described for the Karluk sock- 

 eye fishery by Rounsefell (1958) . A major por- 

 tion of the Karluk River catches were taken in 

 beach seines at the river mouth or in adjacent 

 traps, both of which are nonselective for size. 

 Gill nets never played a dominant part in harvest 

 of the Karluk sockeye salmon. In spite of the 

 absence of gear selective for size, a selection 

 from the middle part of the run was present 

 (Thompson, 1951). 



The Chignik fishery offers another example. 

 Recently Dahlberg (1968) and others before him 

 have pointed out the almost identical catch 

 curves for the Chignik and Nushagak fishery. 

 In the Chignik fishery one can distinguish three 

 major production levels, and the relative posi- 

 tion of these are the same as observed in Nu- 

 shagak (Figure 7). The only difference is that 

 the fall from an initial high production level to 

 an intermediate one came a few years later, 

 1926-1927, in the case of the Chignik fishery. 

 Traps were for a long time the principal fishing 



Gilbert, who wrote in a letter to Commissioner 

 H. O'Malley: 



As a result of this screening process, we are selecting 

 for breeding purposes predominantly the younger or 

 less robust members of the colony, those that are 

 dwarfed by reason of early maturity or lack of growth 

 vigor. The effect of such continued breeding from the 

 least fit of the community must result, it would seem, 

 in the gradual impoverishment of the race and the 

 reduction in size and value of the individuals composing 

 it. 



The inference may be made that the observed 

 shifts in run strength and productivity in Nu- 

 shagak are associated with changes in gear selec- 



JOn 



;6A- 



18 



32 



16 



.s.Chignik 



<?) O) O^ Oi 



O^ O) c^i ^ Oi ^h 



I 35 

 09- 



Figure 7. — Comparison of catches of sockeye salmon in 

 the Chignik and Nushagak fisheries. Curves smoothed 

 by a moving average of 5's. 



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