Randomness of samples was assured by suc- 

 cessively separating a net's catch of live 

 juveniles in a washtub into equal parts with 

 a mesh panel and releasing half of the fish 

 each time until the desired number remained. 



Ages of 807 fish were read in the field from 

 scales dry-mounted between two microscope 

 slides. An additional 2,287 fish were aged 

 on the basis of estimated length alone, as de- 

 scribed later. Annuli criteria were established 

 by examination and by methods described by 

 Clutter and Whitesel (1956), Each scale was 

 read once after which 49 scales were selected 

 at random and read a second time without 

 reference to the first reading. Agreement 

 between first and second readings was 100 

 percent. Although reading scales from samples 

 collected at the end of the summer was com- 

 plicated by early formation of an annulus in 

 September, close agreement was attained in 

 independent readings by two readers. Fork 

 lengths were measured to the nearest milli- 

 meter. 



A close relationship was found between age 

 and length of the migrants sampled from May 

 21 to June 10, the main migration period (fig. 

 12). The migrants fell into two age-length 

 groups: yearlings, which average 83 mm. 

 (range 61 to 96 mm.) and 2-year-olds, which 

 averaged 109 mm. (range 90 to 125 mm.). 

 Since overlap in lengths of the two age groups 

 was almost nonexistent, it was possible to age 

 migrants reliably by their size. There was 

 apparently some digit bias in measuring 2- 

 year-olds, but this did not significantly affect 

 the analysis. 



70- 



CO 



60- 



YEARUMS* 



50- 



(nc|92) 

 i- 82.7 mn. 



40- 



>- 



UJ 



u 

 o 

 m 30- 



D 2-YEAR-OLOS 



(l<:382) 

 i = l09.0 mm. 



20- 



10- 



0-^ 

 60 



70 



£ 



sjm 



^ 



80 



90 



100 



no 



120 



FORK LENGTH (MM) 



Figure 12.— Relationship between age and length of 

 sockeye salmon migrants sampled at Brooks Lake 

 outlet. May 21 to June 10, 1957. 



The mean lengths of migrants from Brooks 

 Lake were compared with those of migrants 

 from other sockeye salmon lakes reported in 

 the literature. Lengths of given age groups 

 from the different lakes varied widely. Aver- 

 age lengths of seaward migrants at Karluk 

 Lake from 1925 to 1936 were invariably much 

 greater than those of migrants at Brooks 

 Lake in 1957 (Barnaby, 1944: table 27). Like- 

 wise, migrants at Lake Dalnee, Kamchatka, 

 from 1935 to 1943 were much larger than the 

 1- and 2-year age groups at Brooks Lake 

 (Krogius and Krokhin, 1948: table 14). Two- 

 year-olds from Brooks Lake, however, were 

 about the same average length as those from 

 Lake Blizhnee, Kamchatka; and both 1- and 

 2-year-olds at Brooks Lake were larger than 

 migrants at Kurile Lake, Kamchatka (Krogius 

 and Krokhin, 1948). Such size differences 

 might be used as a measure of productivity 

 of different nursery lakes as more comparative 

 data become available. 



After mid- June the proportion of 2-year- 

 olds migrating from Brooks Lake dwindled 

 rapidly, leaving only yearling migrants. Fry 

 migrants predominated in September. The 

 overall seasonal age composition was 2 per- 

 cent fry, 42 percent yearlings, and 56 percent 

 2-year-olds (table 6). Since the mesh size of 

 the fyke nets was too coarse to retain fry in 

 the spring, the true percentage was probably 

 somewhat higher than indicated. Migration of 

 some fry was observed in the latter part of 

 May and early June and again in September. 



Table 6 shows the daily catch and percent 

 of the total of each age class captured in each 

 of the three nets. The numbers and ages for 

 each net were compared for the period May 27 

 through June 11 (the peak of the migration) 

 when all three nets were fished simultaneously. 

 Although daily catches and age compositions 

 varied considerably, the overall age composi- 

 tions for each net were in close agreement. 

 Age compositions of the catches of the three 

 nets were similar, indicating that samples from 

 one net site were representative of the popula- 

 tions sampled at the other two sites. The 

 catches were inversely proportional to the 

 amount of water strained — the largest net (no. 

 2) in the fastest, deepest water caught the 

 fewest fish. Based on our observations, an ex- 

 planation of this phenomenon might be that the 



19 



