to spawn. Periodic observations along the stream- 

 hank at night with a lantern in late November and 

 early December in 1963 continued to reveal the 

 presence of pygmy whitefish in the stream. Un- 

 seasonably cold temperature, however, caused ice 

 conditions that precluded intensive observations. 

 About 100 fish were seen just at the mouth of 

 Brooks River during a night dive on December 

 16, 1963. Most of these fish were individually 

 scattered over the stream bottom, although one 

 congregation of 8 to 10 fish may have represented 

 a spawning group. These particular fish darted 

 wildly about upon encountering the underwater 

 spotlight. The water temperature in Brooks River 

 on December 16 was 0.3° C. All adult pygmy 

 whitefish taken in gill nets under ice in South Bay 

 near the river mouth on December 12 and 18 were 

 spent. 



DISCUSSION 



In the Naknek River system pygmy whitefish 

 apparently reach their greatest density in Brooks 

 Lake where they may be the most abundant species 

 in the lake. These conclusions are based on the 

 combined numbers of each species caught in all 

 sampling gears from 1961 to 1963. In Brooks 

 Lake, South Bay, and Iliuk Arm, pygmy white- 

 fish are commonly associated with juvenile sock- 

 eye salmon. This relation merits consideration be- 

 cause of the commercial value of the Naknek 

 River system sockeye salmon. 



Although the association of two species prede- 

 termines some sort of interspecific relation, in fishes 

 it is usually difficult to determine the exact nature 

 of this relation. Larkin (1956), who considered 

 competition in a concise limited sense, points out 

 that competition itself is difficult to separate from 

 other complex interrelations between fish species. 

 Rogers (1961), after carefully considering the 

 diets of young-of-the-year sockeye salmon and 

 three age groups of threespine sticklebacks collect- 

 ed from similar ecological areas of Wood River 

 Lakes, could only conclude that "potential food 

 competition exists." Greenbank and Nelson 

 (1959), in studying the threespine stickleback in 

 Karluk Lake, conclude that "Quantitative infor- 

 mation is insufficient to assess accurately the bene- 

 fit or harm to salmon production caused by the 

 stickleback population." Johnannes and Larkin 

 (1961) could demonstrate -severe competition be- 



tween redside shiners (Richardxonius balteatus) 

 and rainbow trout for amphipods in Paul Lake, 

 British Columbia, only because of long-term data 

 that included preshiner amphipod densities along 

 with feeding habits and growth rates of the trout. 



In the present study it is impossible on the basis 

 of existing data to demonstrate direct interspecific 

 competition in any form between pygmy white- 

 fish and juvenile sockeye salmon or other white- 

 fishes. It is possible, however, that the combined 

 effects of interspecific and intraspecific relations 

 of these species may influence the growth and 

 general well-being of each in various parts of 

 the Naknek system. Although McCart (1963) 

 could not demonstrate direct competition between 

 pygmy whitefish and other whitefishes, he found 

 indications of interactive segregation between 

 whitefishes which resulted in differences in depth 

 distribution and growth rates. He also noted that 

 the large Mac Lure and McLeese Lake pygmy 

 whitefish were the only ones in British Columbia 

 that did not coexist with another species of the 

 genus Prosopiwm. In the present study the largest 

 pygmy whitefish were found in South Bay and 

 Iliuk Arm where three other whitefishes occur 

 (round and humpback whitefish and least cisco), 

 while the smallest pygmy whitefish were found in 

 Brooks Lake where round whitefish is the only 

 other whitefish. Although growth rates of pygmy 

 whitefish in the Naknek system are correlated with 

 different diets, McCart (1963) found no differences 

 in diets of this fish in four lakes where growth was 

 quite different. 



Both pygmy whitefish and juvenile sockeye sal- 

 mon feed heavily on zooplankton in Brooks Lake, 

 although Merrell (1964) points out that during 

 late spring and early summer, insects may be the 

 most important item in the diet of Brooks Lake 

 sockeye salmon (age 1+ and older) . Even though 

 differences in the production of sockeye salmon 

 smolts in Brooks Lake have varied from 60,000 to 

 360,000 during recent years, there has been little 

 difference in the mean size of age 1+ smolts. This 

 suggests that densities of young salmon, together 

 with other environmental influences such as poten- 

 tially competitive dense populations of pygmy 

 whitefish, have not altered the basic growth rate of 

 sockeye salmon in Brooks Lake. 



Interspecific association of juvenile sockeye sal- 

 mon and pygmy whitefish in South Bay and Iliuk 



PYGMY WHITEFISH OF SOUTHWEST ALASKA 



575 



