River contained food similar to that of lake trout from 

 the same area. A char (about 40 cm long) was seen 

 feeding in upper Grosvenor River on 20 May 1962 and 

 was captured by angling. This fish contained several 

 sockeye salmon fry, two of which were still alive. 



Other Species 



Only general observations are available on the other 

 pisciverous fish in the Naknek River system — rainbow 

 trout, juvenile coho salmon, northern pike, and bur- 

 bot. 



Rainbow trout inhabit most of the larger streams in 

 the system and were often taken by angling in the lakes 

 near the mouths of these streams. Sportsmen fish for 

 this species in American Creek and Coville, Brooks, 

 and Naknek Rivers; fish above 60 cm are commonly 

 caught in these locations. No food studies have been 

 made here, but rainbow trout have been observed 

 feeding on young sockeye salmon that were migrating 

 from stream spawning grounds to the lakes and from 

 lake to lake via connecting rivers either as presmolts 

 or smolts. 



Juvenile coho salmon were taken in appropriate gear 

 in many streams and beach areas in the system, but 

 were virtually absent from tow net samples. Because 

 of their relatively small size (no juvenile coho salmon 

 over 130 mm were taken), I would expect coho salmon 

 to be most effective as predators on sockeye salmon 

 during the first few weeks after the sockeye salmon 

 leave the gravel — in streams and lake margins before 

 the sockeye salmon become pelagic. 



Northern pike are widely distributed in the Naknek 

 system wherever suitable habitat is found. The lake 

 areas where northern pike seem to be abundant are the 

 shallow north end of Coville Lake and the shallow 

 waters of Northwest Basin. Generally the habitat in 

 which northern pike are abundant does not contain 

 many juvenile sockeye salmon. Possible exceptions to 

 this occur in Grosvenor River near Grosvenor Lake 

 and in the upper Naknek River where lagoons contain- 

 ing northern pike are closely connected to river areas 

 containing migrating sockeye salmon. Sockeye salmon 

 have not been reported in stomachs of northern pike 

 from this system. 



Burbot have been captured in Iliuk Arm, South 

 Bay, and North Arm (Heard, Wallace, and Hartman. 

 1969), but were never abundant. They were caught in 

 gill nets and trap nets in South Bay, in trap nets in 

 North Arm, and in seines in Iliuk Arm. In Lake 

 Michigan, the stomachs of lake trout and burbot that 

 were captured in gill nets contained the same kinds of 

 fish, but the burbot contained only 74% fish by volume 

 and the lake trout contained 98% (Van Oosten and 

 Deason, 1938). Both species were predators on 

 coregonids. No data are available on the diet of burbot 

 in the Naknek system, but apparently so few are pres- 

 ent that they would not be a significant predator even 

 if sockeye salmon were important in their diet. 



General Significance of Predation 



Although many species of fish and birds are poten- 

 tial or known predators on juvenile sockeye salmon in 

 the Naknek system, the role of predators in determin- 

 ing freshwater survival is unknown. The abundance of 

 smolts from the escapement of 1961 shows that smolt 

 production per adult may be high in spite of predation 

 in the Naknek system. In 1961 a relatively small es- 

 capement of about 350,000 adult sockeye salmon en- 

 tered the Naknek system, of which about 220,000 went 

 to the most distant spawning grounds, American 

 Creek. The production of smolts from the total es- 

 capement to the system in 1961 was about 32 smolts 

 per adult (see footnote 3) — the highest rate recorded 

 for the Naknek system between 1956 and 1963. The 

 survival of these smolts to returning adults in 1966 and 

 1967 was about 15.5%, I3 very close to the long-term 

 average of about 16.5% (Burgner et al., 1969). A dif- 

 ferent distribution or abundance of adult sockeye 

 salmon or predators might result in a much different 

 effect on survival in another year. 



SUMMARY AND SIGNIFICANCE FOR 

 RESOURCE DEVELOPMENT 



Although most stocks of sockeye salmon have the 

 same general life history, each stock is unique because 

 it has its own combination of biological and physical 

 environments. The principal objective of this study 

 was to determine the distribution, abundance, and 

 growth of juvenile sockeye salmon in the Naknek 

 River system, Bristol Bay, Alaska. The work was 

 done from 1961 through 1964. 



The Naknek system contains eight interconnected 

 and generally biologically discrete lakes or basins with 

 different ratios of potential spawning grounds to rear- 

 ing area for sockeye salmon and different densities of 

 juvenile sockeye salmon and associated species of 

 fish. The sockeye salmon was the most common and 

 abundant fish in all basins, followed by threespine 

 sticklebacks, ninespine sticklebacks, and pond smelt. 

 Eighteen other species of potential competitor or 

 predator fish were present. 



Juvenile sockeye salmon in the pelagic areas had a 

 characteristic pattern of abundance in tow net catches 

 during the summer of 1961-64. For the entire system 

 the abundance of age fish increased from early sum- 

 mer to midsummer and then declined to late August. 

 The abundance in late August varied by a factor of 

 about 2.5 and, although data are available for only 4 

 years, the abundance appears to be independent of 

 variations in the number of parents from 1960 to 1963. 



In July the catches of age sockeye salmon in each 

 basin were about proportional to the abundance of 

 contiguous spawning grounds, but by late August this 

 relation no longer existed. This change was at least 



l:, C.J. DiCostanzo, National Marine Fisheries Service. Auke Bay 

 Fisheries Laboratory, Auke Bay, AK 99821, pers. comm. 



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