58 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Variability in life-liistoi-y categories among 

 females can be the cause of considerable change 

 in reproductive potential from year to year, 

 even though tlie number of spawners and sex 

 ratio remain constant. Life-history categories 

 are defined as groups of fish with di tie rent 

 combinations of fresh-water- and ocean-years of 

 life and are denoted by 2 figures; for instance, 5^ 

 denotes fish that migrated to the ocean in their 

 third year of life and returned to spawn in tlieir 

 fifth year. Analysis of the Karluk Lake age data 

 in 1958 shows that 2 major categories dominate 

 the spawning populations, Sj and 64 (table 2). 

 However, in some years one or more other age 

 categories contribute considerable numbers of fish 

 to the run. The salient feature of this population 

 structure (table 2) is the great difl'erence in the 

 length and fecundity relation between life-history 

 categories with 1, 2, and 3 years of ocean life; 

 i.e., is and 64 vereus 63 and 64 versus 63 and 74. 

 Marked annual differences in the abundance of 

 1 -ocean-year, 2-ocean-year, or 3-ocean-year fish 

 could substantially alter the reproductive 

 potential. 



Table 2. — Reproductive potential of the 1958 escapement at 

 Karluk Lake by life-history categories 



1 Based on a sample of 2,108 red salmon from the 1958 escapement. 



2 Midcye-fork length. 



3 Determined by substituting mean lengths into the fecundity equation 

 (fig. 2). 



' The very minor categories. 4;, 65, and 7s, contribute an estimated 1,000,000 

 eggs to the potential egg deposition. 



Sex ratios for each life-history categoi-y must 

 be considered in any study of the reproductive 

 potential of spawning populations. Barnaby 

 (1944) shows that the sex ratio of the Karluk 

 Lake spawning jiopulations varied considerably 

 when important life-histoiy categories varied in 

 dominance. He found over several years that the 

 average proportion of males in the 1-ocean-year 

 categories (43 and .">,) ranged from 100 to 75 per- 

 cent, the 2-ocean-year categories (53 and fij 

 ranged from 62 lo 32 percent, and the 3-ocean- 

 year categories ranged from 38 to 35 percent. 



The reproductive potential and the egg contri- 

 liution from each of the six major life-history 

 categories comprising the 1958 run at Karluk 

 Lake is shown in figure 5. Examination of these 

 data indicates that 89 jwrcent of the eggs for 

 lX)tential deposition came from the two 2-ocean- 

 year categories, 5^ and 64. 



Barnaby (1944) shows that a seasonal pattern 

 of appearance of the different life-history cate- 

 gories exists at Karluk Lake. As the daily com- 

 position of the run changes throughout the season, 

 obviously so does the reproductive potential. It 

 is possible that the commercial fishery could have 

 been concentrated during that seasonal time of 

 migration when important groups such as the 53 

 and 64 categories were moving through the fish- 

 ing grounds. As a result, tlie reproductive 

 potential of the spawning populations could be 

 seriously reduced because of a shift in age com- 

 position to younger ocean-age groups. These 

 fish on a one-for-one basis are less fecund. It 

 is interesting that the 3-ocean-year categories (63 

 and 74) accounted for only about 6 percent of the 

 1958 escapement, which is the lowest contribution 

 by these groups ever recorded (Rounsefell, 1958: 

 156). At the same time the 1-ocean-year cate- 

 gories (43 and 54) accounted for 17 percent of the 

 1954 escapement, which is by several times the 

 highest contribution from those categories ever 

 recorded. Analysis of future Karluk escape- 

 ments will determine if this substantial shift in 

 ocean-age composition is the result of a real trend 

 or merely variability in year-class strength. 



It is concluded that a detailed study of the re- 

 productive potential of the spawning populations 

 is necessary to establisli a basis for fresh-water 

 survival studies of red salmon. It may also 

 serve to help explain, at least in part, the causes for 

 declines in red salmon runs over the jjast decades. 



SUMMARY 



The relation between egg count and mideye- 

 fork length was derived for Brooks and Karluk 

 Lakes red salmon. Comparing recent Karluk 

 Lake data with ptist fecundity studies indicates 

 that a long-term decrease in mean size and fecun- 

 dity of females has occurred. 



Red salmon at Brooks and Karluk Lakes con- 

 sistently had more eggs in the left ovaiy than in 

 the right. 



