PYGMY WHITEFISH PROSOPIUM COULTERI IN THE NAKNEK RIVER 



SYSTEM OF SOUTHWEST ALASKA 



By William R. Heard and Wilbur L. Hartman, Fishery Biologists (Research) 

 Bureau of Commercial Fisheries Biological Laboratory, Auke Bay, Alaska 



ABSTRACT 



The pygmy whitefish is widely distributed through- 

 out the lakes of the Naknek River system in southwest 

 Alaska. It is a small abundant species in some lakes 

 of the system and may occupy a more prominent place 

 in the population dynamics of fishes in the Naknek 

 system than in other geographic areas where it has been 

 studied. Specimens were collected with a variety of 

 sampling gear including gill nets, tow nets, otter trawls, 

 and seines. Pygmy whitefish occurred in all benthic 

 habitats from shallow littoral depths to bathybenthic 

 areas. Seasonally in certain age groups and in certain 

 areas they occurred in limnetic areas of lakes and in 

 streams. In the Naknek system, 18 species, including 

 the young of commercially valuable sockeye salmon 

 and the closely related round whitefish, were ecological 

 associates of pygmy whitefish. 



Two populations, one in South Bay of Naknek Lake 

 and the other in Brooks Lake, were studied in detail. 

 The oldest and largest pygmy whitefish collected was 

 an age V 163-mm. female from South Bay. An age III 

 83-mm. female was the oldest and longest specimen 

 from Brooks Lake. Length frequency distributions 

 from other lakes were intermediate between these 

 extremes. Growth rates were back calculated from 

 polynomial body length-scale length equations for 

 Brooks Lake and South Bay populations. 



Dipteran insects were the principal foods eaten by 

 pygmy whitefish in South Bay. Crustacean plankton 

 dominated their diet in Brooks Lake. In other areas 

 insects and zooplankton were about equal in impor- 

 tance. Growth and insect consumption were correlated 

 positively. 



Spawning occurs in November and December, appar- 

 ently only at night. South Bay fish spawn in lower 

 Brooks River. Eggs in ripe females from South Bay 

 averaged 2.4 mm. in diameter, and the ovaries were 

 16.5 percent of the body weight. The fork length- 

 fecundity relation of Naknek system pygmy whitefish 

 has the equation 



Log E= -2.9552 + 2.7513 Log L 



Both sexes mature earlier in Brooks Lake than in 

 South Bay. 



Slow growth, low fecundity, and short life character- 

 ize pygmy whitefish in Brooks Lake. These factors 

 are compensated for in part by early maturity and 

 probably by a low mortality from fertilized egg to 

 maturity. The wide range of pygmy whitefish popu- 

 lations in the Naknek system probably reflects adaptive 

 responses of a highly plastic species to the wide variety 

 of environmental characteristics found in different 

 lakes of the system. 



Pygmy whitefish, Prosopiwm coulteri (Eigen- 

 mann and Eigenmann), are widely distributed 

 throughout lakes of the Naknek River system in 

 southwest Alaska (fig. 1). These lakes, which are 

 important fresh-water rearing areas for juvenile 

 sockeye salmon, Orworhynchus nerka (Walbaum), 

 are studied by the Bureau of Commercial Fish- 



Note. — Approved for publication March 4, 1965. 



eries to determine factors limiting fresh- water pro- 

 duction of this highly important commercial spe- 

 cies. These studies embrace a variety of limnolog- 

 ical and biological research, including interspecific 

 relations of fishes associated with juvenile salmon. 

 Pygmy whitefish are apparently the most ab- 

 undant species in some lakes of the Naknek system, 

 and it is possible that they may compete directly 



FISHERY BULLETIN: VOLUME 65, NO. 3 



555 



