productivity is that Coville. Lake, which has the 

 shallowest mean depth, the highest water tempera- 

 tures, and the highest primary productivity in the 

 system, apparently has only a small population of 

 intermediate size pygmy whitefish; however, 

 Coville Lake may have denser populations of other 

 species (i.e. pond smelt, humpback whitefish, and 

 juvenile sockeye salmon) than other parts of the 

 system. 



Until comparative data are available on the 

 relative abundance of various food groups and 

 the diets of associated fishes in different areas, it is 

 impossible to determine the role of food availabil- 

 ity or preference for specific foods in evaluating 

 differences in the biology of pygmy whitefish in 

 the Naknek system. Rather than simple differ- 

 ences in diet, growth, or ecological distribution, we 

 feel the dramatic differences found in pygmy 

 whitefish populations in the Naknek system prob- 

 ably reflect widely varying adaptive responses of 

 a highly plastic species to the complex of environ- 

 mental differences found throughout the system. 



SUMMARY 



The pygmy whitefish has the greatest discontin- 

 uous distribution of any fresh-water fish in North 

 America, occurring in the Atlantic, Pacific, and 

 Arctic Ocean drainages. It is widely distributed 

 and locally abundant in lakes of the Naknek River 

 System in southwest Alaska. 



More than 10,000 pygmy whitefish were collected 

 from the Naknek system with seines, otter trawls, 

 tow nets, and gill nets from 1961 to 1963. This 

 species seems to have a prominent role in the dy- 

 namics of some Naknek system fish populations. 



In the Naknek system, pygmy whitefish occur 

 in all benthic areas from shallow littoral depths 

 to the deepest areas available. Seasonally, in cer- 

 tain age groups and in certain areas, they occur 

 in limnetic waters of lakes and in streams. 



Nineteen species, including the closely related 

 round whitefish, occurred in catches with pygmy 

 whitefish in various parts of the Naknek system. 



Polynomial equations were used to express the 

 curvilinear relation between body length and an- 

 terior scale radius. Body length at scale formation 

 is about 25 mm. 



The oldest and largest fish from the two areas 

 studied most intensively was an age V 163-mm. 

 female from South Bay and an age III 84-mm. 



female from Brooks Lake. Length frequency dis- 

 tributions from other areas were intermediate be- 

 tween these extremes. Calculated and observed 

 growth indicated that growth was much greater 

 in South Bay than in Brooks Lake. Both sexes 

 in Brooks Lake showed a tendency to mature at an 

 earlier age than in South Bay. 



Dipteran insects were the principal foods eaten 

 by pygmy whitefish in South Bay. Crustacean 

 plankton dominated their diet in Brooks Lake. 

 In other areas insect and zooplankton foods were 

 about equal in importance. In areas where insects 

 were important in the diet of older fish, the shift 

 from zooplankton to insect foods in age 0+ fish 

 began during the first summer of life. A positive 

 correlation between growth and insect utilization 

 was found. 



The fork length-fecundity relation of Naknek 

 system pygmy whitefish is expressed by the equa- 

 tion 



Log E= -2.9552+2.7513 log L. 



where E equals number of eggs per female and L 

 equals fork length of the fish. Fecundity in Nak- 

 nek system fish exceeds that in Lake Superior fish. 



Spawning occurs in November and December. 

 South Bay fish move into Brooks River for spawn- 

 ing only at night. Eggs in ripe fish from South 

 Bay averaged 2.4 mm. in diameter, and the ovaries 

 were 16.5 percent of the body weight. 



Potential interspecific competition exists be- 

 tween pygmy whitefish and juvenile sockeye 

 salmon, particularly in Brooks Lake where foods 

 are similar and the whitefish are numerous. 



Slow growth, low fecundity, and short life 

 characterize Brooks Lake pygmy whitefish. 

 These factors must be compensated for by lower 

 mortality from fertilized egg to maturity than in 

 the South Bay population, which is characterized 

 by fast growth, higher fecundity, and longer life. 



The wide range in growth rate, fecundity, lon- 

 gevity, and diet of populations of pygmy white- 

 fish in the Naknek system is probably due to the 

 adaptive responses of a highly plastic species to 

 the variety of environmental characteristics, such 

 as water quality and clarity, drainage geology, 

 phytoplankton productivity, lake morphometry, 

 fish species, and food organism associations found 

 in different parts of the system. 



PYGMY WHITEFISH OF SOUTHWEST ALASKA 



577 



