Arm is complicated by several factors. First, a 

 greater number of other associated species occur 

 in these areas than in Brooks Lake. Second, in 

 addition to serving as primary rearing areas for 

 salmon produced in adjacent spawning areas such 

 as Brooks River and M argot Creek (a tributary 

 of Iliuk Arm), both South Bay and Iliuk Arm, of 

 necessity, serve as migration lanes for salmon 

 produced in upsystem areas. This point is further 

 complicated by interlake movement whereby some 

 juvenile sockeye salmon begin their nursery lake 

 existence in upstream lakes (i.e. Coville and 

 Brooks), then migrate into downstream nursery 

 areas (i.e. Iliuk Arm and South Bay) to complete 

 their first year of life. 5 Tims, the juvenile, sockeye 

 salmon populations in South Bay and Iliuk Arm 

 are frequently undergoing dramatic changes in 

 density apart from normal fluctuations in the local 

 population. Although pygmy whitefish feed 

 primarily on insects in South Bay and Iliuk Ann, 

 the diet of young sockeye salmon in these areas is 

 not known. It may be that no possible food com- 

 petition exists between these species in South Bay 

 and Iliuk Arm. 



The reasons for the marked differences in the 

 biology of pygmy whitefish populations in Brooks 

 Lake and South Bay are poorly understood. 

 Pygmy whitefish in Brooks Lake grow slower, 

 mature earlier, and live shorter lives than those in 

 South Bay or Iliuk Arm. Consequently, spawn- 

 ing females are younger, significantly smaller, and 

 less fecund in Brooks Lake. Yet, the species is 

 extremely successful in Brooks Lake, as evidenced 

 by abundance. Factors contributing to this suc- 

 cess undoubtedly deal with lower mortalities from 

 fertilized egg; to maturity. Because of early matu- 

 rit v, short life span, and small size, pygmy white- 

 fish in Brooks Lake fit the concept of a "dwarfed 

 or small form" discussed by Svardson (1957), 

 Aim (1959), and Fenderson (1964). As pointed 

 out by Aim, a "dwarfed form" with short life and 

 early maturity is distinct from a slow-growing 

 "normal fonn" which has greater longevity and 

 matures at an older age but still at a small size. 

 Dwarfism may provide a species with advantages 



^'Summary report of studies "ti the optimum escapement of 

 sockeye salmon in southwestern Alaska, 1961—62. Prepared by 

 the Bureau of Commercial Fisheries Biological Laboratory. Aula* 

 Bay, Alaska, and Fisheries Research Institute, University of 



Washington, Spattlc ( Manuscript on tile at tin- BCF Laboratory.) 



in survival and competition ( Lindstrom and Nils- 

 son, 1962; McCart, 1963; and Fenderson, 1964). 



On the basis of recent data from Lake Alek- 

 nagik and Chignik Lake, Peter J. McCart (per- 

 sonal communication) believes that two distinct 

 sub-populations of pygmy whitefish may occur 

 sympatrically in these lakes. One form, which is 

 generally larger, is a river-oriented insect feeder 

 with low gill raker counts and is apparently con- 

 fined to shallow water. The other form is a lake- 

 oriented plankton feeder with high gill raker 

 counts and inhabits deep water. These criteria, in 

 part, apply to some of the differences found in 

 populations in the Naknek system. This is partic- 

 ularly time with the insect feeders in South Bay 

 where the population is strongly oriented to 

 Brooks River and the relatively shallow waters of 

 South Bay. In other parts of the system, however, 

 differences in ecological distribution represent 

 exceptions to this general scheme. In Iliuk Arm, 

 large fast-growing insect feeders occur from shal- 

 low beaches to maximum depths of 168 m., whereas 

 in Brooks Lake, slow-growing insect feeders occur 

 from the shallow to the deepest depths. Although 

 we have not studied meristic variation of popula- 

 tions of pygmy whitefish in the Naknek system in 

 detail, the insect feeders in South Bay and Brooks 

 River have lower gill raker counts than the plank- 

 ton feeders in Brooks Lake. Eschmeyer and 

 Bailey (1954, p. 174) point out that gill rakers 

 from pygmy whitefish in rivers, or lakes domi- , 

 nated by rivers, tend to be fewer in number and 

 shorter in length than those from lacustrine en- 

 vironments. Whether differences found in popu- 

 lations of pygmy whitefish in the Naknek system 

 represent genetically distinct subpopulations or 

 the adaptive, responses of the species in utilizing 

 the many environments present in the system can- 

 not be determined without additional study. 



Differences in diet in various parts of the system 

 have been discussed and correlated with growth 

 rates. Actually, growth rates are correlated not 

 only with the degree of insect utilization but also 

 with the rate of phytoplankton productivity in 

 various areas. Primary productivity is relatively 

 high in South Bay and Iliuk Ann, low in Brooks 

 Lake, and intermediate in North Arm and Gros- 

 venor Lake. 6 A notable exception to correlating 

 growth rates of pygmy whitefish with primary 



576 



* Sep footnote 2 on p. 557. 



U.S. FISH AND WILDLIFE SERVICE 



