of 150 age fish per tow in 1962. North Arm had 

 a spawner density of 55 per square kilometer of 

 lake in 1961 and a catch of age fish of 0.5 per 

 tow in 1962. Migration of presmolt juveniles, 

 however, results in the accumulation of young 

 in the rearing areas of Naknek Lake regardless 

 of the distribution of spawners. The studies have 

 run too few years to determine the relation be- 

 tween the abundance of age fish and various 

 levels of the parent popuiauion. 



The abundance and growth of juvenile sock- 

 eye salmon and other species and the primary 

 productivity of the lakes varied between years 

 and among the lakes. Differences in primary pro- 

 ductivity between years were accompanied by 

 marked differences in growth of juvenile sockeye 

 salmon, independent of their abundance. The 

 abundance of juveniles was greater in 1962 than 

 in 1961, but the rate of growth was greater in 

 1962. The primary productivity, on the other 

 hand, was greater in 1962 than in 1961 because 

 of differences in climate. The species and abun- 

 dance of fish associated with the juvenile sockeye 

 salmon vary among the lake.s and among areas 

 within the lakes. Threespine sticklebacks were 

 universally present, and their abundance was 

 matched only by pond smelt in Lake Coville and 

 pygmy whitefish in Brooks Lake. The areas of 

 the Naknek system that yielded the largest 

 catches of juvenile sockeye salmon or the fastest 

 growing juveniles also yielded the largest 

 catches of associated species. The role of the as- 

 sociated species as competitors or predators, or 

 as buffers between predators and juvenile sock- 

 eye salmon, is unknown. Several potentially im- 

 portant predator fish are present in the Naknek 

 system, but their significance is not known. 



Lakes of the Naknek system have limnological 

 characteristics that fall between those that are 

 characteristic of lakes of the Mainland Systems 

 and also the other lakes of the Peninsula Sys- 

 tems. Lakes of the Naknek system are richer 

 than the mainland lakes in total dissolved solids, 

 total alkalinity, sodium, silica, iron, and man- 

 ganese and generally richer in many of the other 

 items measured. The large quantities of igneous 

 materials in the watershed and wind-borne ma- 

 terials from the ocean apparently contribute 

 substantially to this richness. These lakes are 

 influenced by the oceanic climate ; their ice 

 covers break up relatively early in the spring. 

 Thermal stratification is seldom pronounced, 



and strong wind action mixes surface waters 

 with deeper waters from time to time during 

 the summer. Rates of carbon fixation by photo- 

 synthesis are relatively high, and the standing 

 crops of phytopiankton are similar to those of 

 other peninsula lakes. Because of differences in 

 drainage and basin types, lakes in the Naknek 

 system nearly encompass the range of types of 

 sockeye salmon nursery lakes along the Alaska 

 Peninsula, although Chignik and Black Lakes 

 rank higher than any Naknek lakes in photosyn- 

 thetic rates and chlorophyll values. 



Data on the relation of smolt production to 

 escapement in the Naknek system in 1954-60 

 show an increase in numbers of smolts produced 

 with increased escapement up to about 1 million 

 fish. Accurate determination of optimum es- 

 capement from reproduction curves based on 

 smolt-escapement relations is dependent on 

 knowledge of mortality rates in the ocean. For 

 the Naknek system, estimates of total ocean 

 mortality for sockeye salmon from 3 years of 

 smolt migration ranged from 77.6 percent to 

 95.2 percent and averaged 83.5 percent (no cor- 

 rection for a high seas fishery) . 



If total ocean mortalities range around 83.5 

 percent, maximum yields may be realized with 

 escapements of 0.6 to 1.0 million. The presently 

 known spawning areas have a capacity of about 

 1.3 million spawners. Escapement levels do not 

 appear to have any effect on the size of age I 

 smolts or the percentage of the progeny that 

 migrates seaward as age II smolts. The Naknek 

 lakes are richer in basic nutrients and generally 

 have higher rates of phytopiankton production 

 than the mainland lakes. Major differences in 

 climate between yeai's probably influence the 

 growth of young sockeye salmon more strongly 

 than do differences in their density. At present 

 we do not know whether the upper limit on the 

 production of smolts is imposed by the capacities 

 of the spawning areas, the capacities of the 

 nursery areas, or a combination of several fac- 

 tors that may or may not include these two. 



Uj^ashik System 



The Ugashik system on the Alaska Peninsula 

 is the southernmost of the major river systems 

 that drain into Bristol Bay. The system consists 

 of two lakes. Upper and Lower Ugashik, which 

 total 385 km.- Our studies in the Ugashik sys- 

 tem included limnological observations, con- 



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U.S. FISH AND WILDLIFE SERVICE 



