Table 21. — Estimated biomass and population numbers of 



walleye pollock by subarea and for all subareas combined. 







1976 Bering Sea spring trawl survey.' 

















Proportion 





Proportion 









Percentage 

 frequency of 



Mean 

 CPUE 



Estimated 

 biomass 



of total 

 estimated 



Estimated 

 population 



of total 

 estimated 



Mean 



size 





Weight 

 (kg) 



FL 



Subarea ; 



occurrence 



(kg/km) 



(t) 



biomass 



(millions) 



population 



(cm) 



Inner shelf 



















4N 



68.2 



0.92 



1,706 



0.003 



298.1 



0.066 



0.0% 



9.9 



4S 



75.0 



1.27 



5,502 



0.008 



1,052.1 



0.234 



C.005 



9.9 



I 



49.0 



2.77 



13,595 



0.020 



1,123.4 



0.249 



0.012 



11.7 



Outer shelf 



















and slope 



















3 



89.7 



( 36.54) 



(171,750) 



0.253 



(801.1) 



0.178 



0.214 



26.6 



3 Slope 



90.9 



(15.41) 



(2,986) 



0.004 



(4.4) 



0.001 



0.672 



45.1 



2 



92.1 



(119.24) 



(445,281) 



0.655 



(1,164.7) 



0.259 



0.382 



36.0 



2 Slope 



80.0 



(90.54) 



(38,673) 



0.057 



(61.1) 



0.014 



0.633 



42.9 



All subareas 



















combined 



77.0 



(34.00) 



(679.492)' 





(4,504.9) 





0.151 



20.5 



Parentheses indicate estimates that may be badly biased due to sampling problems. 

 : See Figure 3. 

 '95% confidence limits: 480,060-878,925 t. 



Of the total population biomass estimated from the 1976 spring 

 survey, 71% was located on the outer continental shelf and upper 

 slope in subareas 2 and 2 Slope, 26% in subarea 3N and 3S, and 

 only 3% in inner shelf subareas 1, 4N, and 4S (Table 21). 



The total number of walleye pollock within the study area was 

 estimated to be 4.50 billion individuals that were distributed 

 among geographical subdivisions of the study area quite different- 

 ly from the population biomass. Only 27°7o of the total number 

 were located in subareas 2 and 2 Slope, as opposed to 71 % of the 

 biomass; 55% of the individuals occurred in the inner shelf (sub- 

 areas 1, 4S, and 4N), representing only 3% of the total apparent 

 biomass. 



Size composition. — Walleye pollock ranged from 7 to 90 cm 

 FL, with an overall mean fork length of 20.5 cm (based upon 

 38,231 field measurements; Fig. 29). Populations in subareas 1, 

 4S, and 4N were composed almost entirely of small juveniles 

 (overall mean fork length for each subarea 1 1.7, 9.9, and 9.9 cm, 

 respectively). Populations in geographical subareas along the 

 outer continental shelf and upper slope were composed of mixed 

 sizes showing a broad range around each mean fork length. 



Geographical subareas 3S and 3N showed substantial propor- 

 tions of individuals in the size ranges 10-12 cm and 17-21 cm. The 

 proportion of these small size groups appeared to decrease from 

 north (subareas 3N and 3S) to south (subarea 2) along the outer 

 continental shelf. 



Populations in subareas 2, 2 Slope, and 3 Slope differed from 

 all other geographical regions in that their apparent size-frequency 

 distributions mainly consisted of large (>30 cm) individuals. 

 Mean fork lengths in these deepwater areas were subarea 2, 36.0 

 cm (range 10-82 cm); subarea 2 Slope, 42.9 cm (range 17-90 cm); 

 and subarea 3 Slope, 45.1 cm (range 34-66 cm). 



Age composition. — Estimates of age-frequency distribution 

 were determined from an overall collection of 846 male and 1,144 

 female saccular otoliths. The ranges in ages observed were males, 

 1-14 yr, and females, 1-15 yr. The estimated numbers of in- 

 dividuals within each age group are summarized in Table 22. 

 However, because estimates of walleye pollock abundance for 

 1976 may have been biased low by sampling problems, the esti- 

 mated numbers at each age (particularly in deepwater subareas 2, 

 2 Slope, 3N, 3S, and 3 Slope) are of uncertain accuracy. Relative 



age distributions between different geographical regions of the 

 survey area are compared in Figure 30. 



Overall, 59.7% (2.69 x 10' individuals) of the estimated 

 population were distributed within age group 1, and 90. 1% (4.06 

 x 10' individuals) were observed to be 4 yr of age or less. Geo- 

 graphical subareas 1 , 4S, and 4N accounted for 91 .3% of all age-1 

 individuals, and nearly all walleye pollock taken within those 

 areas were only 1 or 2 yr of age. 



Populations within geographical areas along the outer conti- 

 nental shelf contained fewer age-1 and age-2 individuals and 

 higher proportions of large, old (>4 yr) individuals. Deepwater 

 subareas 2 Slope and 3 Slope showed relatively large proportions 

 of age groups 7-10. 



Sex ratio. — Proportions of females observed in components of 

 the estimated walleye pollock population are summarized in Table 

 23. The overall proportion of females was 0.43, suggesting either 

 1) a true disparate population sex ratio, or 2) sampling biases 

 causing underestimation of females, perhaps due to decreased 

 availability to survey trawling. If underestimation of females did 

 occur, its cause was apparently not age specific or isolated to 

 spawning individuals, since all age groups between 1 and 10 yr 

 showed proportions ranging between 0.33 and 0.46. Females, 

 however, did predominate in deepwater subareas 2 Slope and 3 

 Slope. 



Length-weight relationship. — A total of 690 individuals from 

 the walleye pollock populations in otolith areas B and D (Fig. 4) 

 were measured for fork length and weight. The results are sum- 

 marized in Table 24 and Figure 3 1 . 



The length-weight relationships of males did not significantly 

 differ between north and south populations. However, the rela- 

 tionship observed for females indicated that individuals from the 

 southern population (otolith area B) were significantly heavier 

 (6-14%) at length, perhaps due to a higher proportion of ripe 

 spawning individuals. 



The overall equation, W = 0.0034 Z, 3 -"", was used for all 

 computations of population numbers requiring a length-weight 

 relationship. 



Age-length relationship and growth. — Age-length keys were 

 calculated from age data of 1,990 fish, and the mean fork length 



41 



