species combinations of fishes, and food organisms 

 are interwoven in a complex of relations that re- 

 sult in distinctly different environments. Differ- 

 ences in growth rates, longevity, and food habits 

 of pygmy white-fish in the Naknek system prob- 

 ably reflect adaptive responses to these overall en- 

 vironmental differences and not simply the avail- 

 ability or use of certain food items. 



The differences we found in Prosopiwm coulteri 

 populations in Brooks Lake and South Bay-Iliuk 

 Arm parallel the differences in Coregomi-s peled 

 (Gmelin) populations in the Swedish lakes Vjom- 

 sjon and Uddjaur-Storavan (Lindstrom and Nils- 

 son, 1962). In Sweden, 0. peJ-ed was a slow-grow- 

 ing plankton feeder in Lake Vjomsjon and a fast- 

 growing insect feeder in Lakes Uddjaur-Storavan. 

 As previously discussed, P. coulteri is a slow-grow- 

 ing plankton feeder in Brooks Lake and a fast- 

 growing insect feeder in South Bay-Iliuk Arm. 

 Lake Vjomsjon had fewer associated whitefish 

 species, proportionately less littoral area, and 

 probably lower productivity than Lakes Uddjaur- 

 Storavan. In the Naknek system, Brooks Lake 

 has fewer associated whitefish species, less littoral 

 area, and lower productivity than South Bay- 

 Iliuk Arm. The observed plasticity of the genus 

 Prosopiwm in response to environmental differ- 

 ences in the Naknek system is similar to that 

 widely recognized in coregonid and leucichthid 

 whitefishes (Walters, 1955; Svardson, 1957; and 

 others) . The variability in meristics and morphol- 

 ogy found in pygmy whitefish by McCart (1963) 

 also emphasizes this plasticity in Prosopiwm. 



REPRODUCTION 



Data on pygmy whitefish reproduction were 

 collected from various areas as follows: sex ratio 

 and age and size at maturity — South Bay and 

 Brooks Lake; fecundity — South Bay, Brooks 

 Lake, and North Arm; and seasonal maturation 

 and spawning behavior — South Bay and Brooks 

 River. 



SEX RATIOS 



Only a few large sampler from Brooks Lake and 

 South Hay were processed for sex ratios, but they 

 revealed nearly equal ratios ((able !>). The largest 

 specimens were almost always females (table 7), 

 a phenomenon undoubtedly due to the greater 

 longevity and the faster growth rate of females. 



These larger females, however, constituted a nu- 

 merically minor segment of the population. Esch- 

 meyer and Bailey (1955) and McCart (1963) also 

 found females to be the oldest and largest fish in 

 their collections. 



Table 9. — Sex ratios of pygmy whitefish, Brooks Lake and 

 South Bay, collected during the summers 1961-62 



Location and date 



Brooks Lake: 



Aug. 7, 1961. 



June 29, 1962 

 South Bay: 



July 23, 1962. 



Aug. 24, 1962 



Sex ratio 



females to 



males 



1:0.92 

 1:1.08 



1:1. 13 



1:0.82 



AGE AND SIZE AT MATURITY 



The degree of maturity in age groups I and II 

 varied between lake populations and between 

 sexes within a single population (table 10). In 

 Brooks Lake 10 percent of the females and 36 per- 

 cent of the males reached sexual maturity during 

 their second growing season (age 1+ ). In South 

 Bay no females and only 2 percent of the males 

 matured as age 1+ fish. In both lakes more than 

 95 percent of the age 11+ fish and all of the older 

 fish were mature. 



Table 10. — Age at maturity of pygmy whitefish collected 

 during the summer and fall from Brooks Lake and South 

 Bay, 1961-62 



In Brooks Lake and South Bay, only a slight 

 tendency exists for males to mature at a smaller 

 size than females. In contrast, Eschmeyer and 

 Bailey (1955) found 100 percent of the males ma- 

 ture at sizes smaller than the smallest mature 

 females. Because of the great differences in 

 growth rates in the Naknek system, there is no 

 overlap in the size at maturity between Brooks 

 Lake and South Hay pygmy whitefish (table 11). 



572 



U.S. FISH AND WILDLIFE SERVICE 



