C/5 

 I- OL 



Z LU 

 UJ 2 



a. CL 



CO 



>-in 



uj m: 



o< 

 O _] 

 <r 

 a. ± 



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Q 

 (f) UJ 



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 Q- 



1957 1958 1959 I960 



ESCAPEMENT YEAR 



1961 



Figure 10. — Comparison of relative size of sockeye salm- 

 on escapement, abundance of progeny in lakes (based 

 on tow net catches), and smolts in Wood River (based 

 on fyke net catches) , Wood system, parent escapement 

 years of 1957-61. 



catches for the day (or days) on which the 

 samples were taken. Smolts were measured in 

 the fresh state soon after capture. 



Wood System 



The Wood system showed two general levels 

 of production of smolts (index points) per 1,000 

 adults in the escapement, the high level (1951 to 

 1954) was 0.50 to 1.87 index points (base of 

 1.00), and the low level (all other years from 

 1949 to 1961) was 0.10 to 0.27 (table 26). The 

 cause of the considerable difference between the 

 two levels is not known — it might be due to un- 

 usually good conditions for survival in the lakes 

 or to a consistent error in indexing smolt abun- 

 dance from 1951 to 1954. 



The index estimates of smolt abundance in the 

 Wood system for later years, 1957-61, can be 

 checked against estimates of abundance at two 

 other stages of fresh-water residence — the rela- 

 tive size of escapements and the abundance of 

 progeny in the lakes (based on tow net samples 

 in late August) . The three estimates of abun- 

 dance had the same general changes from 1957 

 through 1961 (fig. 10). 



Table 26. — Number of sockeye salmon in escapements and 

 abundance, age composition, and mean length of smolts pro- 

 duced, by year of spawning. Wood system, 191,9-61 



[Size of escapements for years 1949-52 based on stream surveys only] 



Smolts 

 pro- 

 Year of Adults Smolts dund As'' composi- Mean length ' 

 spawning in escape- produced per 1.000 tion of smolts of smolts 



ment spawners Age 1 Age 11 Age 1 Age II 



Index Index 



Thousands points points Percent Percent Mm. .Mm. 



1949 101 10 10 _ _. -91 



1950 452 115 25 87 13 =87 '103 



1951 458 299 65 94 6 ' 86 107 



1952 227 425 1 87 99 1 87 102 



1953 516 290 .56 75 25 85 95 



1954 571 286 50 89 11 82 93 



1955 1,383 215 16 62 38 77 102 



1956 773 164 20 97 3 82 105 



1957 289 59 20 97 3 88 114 



1958' 960 255 27 86 14 88 102 



1959' 2.209 508 23 95 5 82 98 



I960' 1.016 167 16 92 8 80 102 



1961 ' 461 82 18 92 8 83 104 



' Fork length of live anesthetized fish. 



- Based on several samples taken during the main migration season 

 but not weighted by catch. 



^ Age composition and mean length approximated in 1958 because of 

 difficulty in determining age of smolts. 



' Smolt data furnished by Alaska Department of Fish and Game for 

 1961-63. 



The relation between numbers of smolts pro- 

 duced and numbers of adults in the parent es- 

 capement in the Wood system (fig. 11) is nearly 

 linear in years when production per spawner 

 was low (years other than 1951-54). Since the 

 cause of the high rate of smolt production from 

 1951-54 is unknown, all points on figure 11 must 

 be given equal weight, and, therefore, optimum 

 escapement in terms of smolt production cannot 

 be determined from these data. 



600 

 500 

 400 

 300 



0,5 1,0 I 5 2 25 



ADULTS IN ESCAPEMENT (MILLIONS) 



Figure 11. — Relation between smolt production (indexed 

 by catches made in fyke nets in Wood River) and 

 number of sockeye salmon in parent escapement, 1949- 

 61, Wood system. The figure beside each point is the 

 year of the parent escapement. 



440 



U.S. FISH AND WILDLIFE SERVICE 



