GRAYLING OF GREBE LAKE 



323 



these were individuals moving toward Grebe 

 Lake, ostensibly to spawn in its tributaries. 



From the weir counts it may be concluded that: 

 (1) currently far more grayling than trout use 

 Grebe Lake tributaries for spawning; (2) in 

 tributaries, competition between species for spawn- 

 ing facilities seems minimal; (3) the Gibbon 

 River between Grebe and Wolf Lakes is used by 

 trout and grayling in about equal numbers and is 

 thus perhaps a site of active competition for 

 reproductive locations; (4) grayling-to-trout ratios 

 based on weir counts for any single tributary are 

 not indicative of proportions of spawners of the 

 two kinds in Grebe Lake. 



Length frequencies 



Length-frequency data were taken on samples 

 of adult grayling trapped in both the 1953 and the 

 1954 seasons. Polygons of the 1953 data have 

 two distinct modes in the female segment of 

 spawners, and one in the male. In the 1954 

 material, three peaks are evident for males and 

 two for females (fig. 12). These crests could 

 reflect different age groups in the population. 

 However, growth of grayling in the Grebe Lake 

 watershed was so small in later life that age as- 

 sessment was essentially impossible (see age and - 

 growth, p. 333). 



Female grayling dominated the sizes below 11.4 

 inches (total length) in 1953 and below 12.2 inches 

 in 1954. This differential size distribution of 

 males and females is attributable to faster growth 

 in males than in females (as reported for the 

 grayling in Norway, Huitfeldt-Kaas, 1927). 



Hybrid trout lengths were much more variable 

 than those of the grayling. Although trout 

 length-frequency polygons show peaks (fig. 13), the 

 numbers of trout comprising each group were so 

 few that the modes expressed cannot be considered 

 as reliable indicators of modal lengths of succes- 

 sive age-groups. Unlike the grayling (where 

 males grew faster than females) female hybrids 

 were of a greater average length than males 

 (fig. 13). 

 Sex ratios 



The potential egg production of a system 

 depends on the number of female spawners as 

 well as upon their individual capabilities. Gray- 

 ling in the blockaded streams were enumerated 

 by sex as they were passed over the barriers. 



The males were separated from the females on 

 the basis of the enlarged, sharply pointed, dorsal 

 fin that reached almost to the adipose fin. This 

 fin in the females is smaller and rounded dorso- 

 caudally. 



During the early part of the spawning season 

 each year, males of the grayling outnumbered 

 females in the traps on tributaries. As the runs 

 progressed, sex ratios assumed a more nearly 

 1:1 ratio and ended that way. Combined data 

 from 1953 showed 10 females for every 24 males 

 that entered Hatchery Creek trap (table 14). 

 That overall proportions may change from year 

 to year is suggested by the fact that the ratio of 

 all grayling trapped in Hatchery Creek in 1954 

 was inverse: 10 females to 7 males. This may 

 have been due to an actual decrease in relative 

 numbers of male grayling in Grebe Lake between 

 the two seasons. 



Table 14. — Ratios of females to males (and sample size) 

 for spawning migrants of the grayling in the Grebe Lake 

 system 



Gustafson (1949) found a 1:1 ratio (93 females 

 to 92 males) among 186 grayling trapped during 

 spawning migrations from Lake Storsjo in Jamt- 

 land, Sweden. Ward (1951) reported only 1 fe- 

 male to 3 males on the Cold Creek (Athabaska 

 drainage, Alberta, Canada) spawning grounds but 

 a ratio of 5.1 females per male at the time he 

 trapped fish for spawn taking purposes. 



Correct identification of the sexes in the hybrid 

 trout depended upon the observable presence of 

 eggs or milt. Of 234 ripe trout captured in 1953, 

 80 were females and 154 were males (ratio 1 : 1.9). 

 In 1954, 141 females and 164 males were identified 

 (ratio 1:1.2). 



For the grayling, age on attainment of sexual 

 maturity was at least 3 years. In the hybrid 

 trout, it was 2 years in the males, and 3 in females 

 (see age-and-growth, p. 334). 



