partly due to migration of age fish — generally from 

 basins of greater abundance offish to others of lesser 

 abundance. The larger and faster growing fish proba- 

 bly were the first to migrate. Not all basins were in- 

 volved in these migrations. 



In the Naknek system smolt production has varied 

 only about twofold with parent escapements of 

 350,000 to 2,000,000 (escapements of less than 300,000 

 have produced markedly fewer smolts). Several fac- 

 tors are suggested as contributing to this relatively uni- 

 form production of smolts. The maintenance of a 

 minimum level of fry production is enhanced by the 

 presence of several major spawning units or races in 

 widely separated spawning grounds of different types. 

 This combination helps ensure against a total loss of a 

 year's production of eggs and alevins due to adverse 

 physical conditions on the spawning grounds. Exam- 

 ples of the value of having different types of habitat 

 are: scouring action of floods would not affect beach 

 spawning areas; extreme freezing would not greatly 

 reduce the flow in major rivers connecting lakes; and 

 warm dry weather causing low lake levels and low 

 flows in small streams would increase the flow of 

 streams fed by snow and icefields. The possibility of 

 full utilization of fry is greatly enhanced by the pres- 

 ence of several connected lakes and the migratory be- 

 havior of the juvenile sockeye salmon during their first 

 summer. 



No indications that the population of juvenile sock- 

 eye salmon was near its upper limit were apparent 

 during this study. In other systems the first obvious 

 effect of too high populations is a reduction in growth. 

 Such a reduction was not evident in juveniles in the 

 lakes of the Naknek system in 1961-64 and apparently 

 did not occur in the period 1957-65, as evidenced by 

 the size of age I smolts — age I smolts from the Naknek 

 system are as large as, or larger than, those of other 

 Bristol Bay systems (Burgner et al., 1969). Much of 

 the variation in the average length of age I smolts 

 (-8.5% to + 6.6% of the mean of 99.4 mm) in the Nak- 

 nek system is thought to be due to variations in grow- 

 ing conditions in the spring just before the smolts leave 

 (Burgner et al., 1969). 



The data on abundance and growth of juvenile sock- 

 eye salmon and the distribution of the escapement and 

 spawning grounds indicate the possibility that produc- 

 tion of sockeye salmon in the Naknek system could be 

 greatly increased. Two of the major basins. North 

 Arm and Brooks Lake, which constitute about 35% of 

 the system, are now producing relatively few 

 juveniles. The low production of juvenile salmon in 

 both basins appears to be the result of too few fry 

 being produced by the spawning grounds, but the 

 reason for the low production of fry differs in the two 

 basins: North Arm has limited but heavily used 

 spawning grounds, whereas Brooks Lake has appar- 

 ently adequate but lightly used spawning grounds. 



North Arm contains about 24% of the rearing area 

 of the system but only about 2% of the spawning 



grounds (and usually receives about 2% of the es- 

 capement) and the basin does not receive juveniles 

 from other areas. Even full use of all the present 

 spawning grounds in North Arm would probably re- 

 sult in too few juveniles to use the rearing area fully. 



Ninety-five percent of the area of potential spawn- 

 ing grounds and 90% of the escapement in North Arm 

 are in Bay of Islands Creek and most of the rest is 

 distributed among seven small streams. Bay of Islands 

 Creek runs about 27 km from a high tundra lake down 

 to North Arm. A falls impassable to salmon is located 

 about 14 km upstream from North Arm. The probable 

 difficulty in making the falls passable and the potential 

 of the stream above the falls for production of sockeye 

 salmon are unknown. It is possible that the present 

 production of sockeye salmon in North Arm could be 

 increased significantly by simply making all of Bay of 

 Islands Creek accessible to spawners. The lake prob- 

 ably could support 10 to 20 times the present density of 

 juvenile salmon. The increase in fry production re- 

 quired to produce the numbers of lake residents North 

 Arm could support could be obtained from a combina- 

 tion of enhancement techniques used elsewhere. 



The reason for the low production of juvenile sock- 

 eye salmon by Brooks Lake is not clear. The major 

 spawning area. Headwater Creek, has an estimated 

 spawning ground capacity of about 40,000 adult sock- 

 eye salmon, but the largest number recorded in the last 

 20 yr was about 1 1 ,000. An intensive study of the biol- 

 ogy of the sockeye salmon of Headwater Creek could 

 be expected to reveal the time, place, and cause of 

 mortality in fresh water. With this information action 

 could be taken to bring Brooks Lake into full produc- 

 tion. 



Three factors in the biology of juvenile sockeye 

 salmon of the Naknek system are of special signifi- 

 cance to the managers of the resource: (1) the abun- 

 dance of smolts each spring has been fairly constant 

 for the system as a whole and not closely related to the 

 abundance of the parents, or from 1961-64, apparently 

 even to the abundance of age fish during early sum- 

 mer, (2) the apparent growth of juvenile sockeye 

 salmon and potential competitor species was not re- 

 lated to the abundance of these fish in any lake of the 

 Naknek system, and (3) two major lakes, constituting 

 about 35% of the rearing waters, do not receive age 

 sockeye salmon from other basins and are supporting 

 relatively few sockeye salmon. 



These three factors and their causes and effects 

 could form the basis for a program to increase the 

 production of sockeye salmon by the Naknek River 

 system. 



The question of what escapement of adult sockeye 

 salmon is needed to ensure full production of juveniles 

 is of primary importance to fishery managers. From 

 1961 to 1964. as few as 350,000 adult spawners were 

 apparently adequate in the Naknek system. However, 

 the special circumstance involved, i.e., the majority of 

 fish in this low escapement used one spawning area 



51 



