Female 



AGE (year) 



Figure 32. — Von Bertalanffy growth curves for male and female walleye pollock, 1976 Bering Sea spring trawl survey (selected ages). Symbols indicate 



the mean length at each age. 



P = e~ 



.-o.ioiL 



(29) 



with the fork length, at 50% maturity, equal to 34.2 cm. 



By applying Equations (28) and (29) to the respective expanded 

 age-length table (consisting of the estimated number of individ- 

 uals in the population at each length and age), it was possible to 

 approximate the percentage of sexually mature individuals within 

 each age class (Table 26). However, because individuals within 

 older age classes at a given length can be expected to be 

 represented by a higher proportion of mature individuals, the esti- 

 mates presented in Table 26 include the following potential biases: 

 The percentage mature within young age classes (2 and 3 yr) may 

 be somewhat overestimated; and the percentage mature within 

 oldeT age classes ( >4 yr) may be slightly underestimated. 



By summing the estimated number of individuals within each 

 gonad condition code (Table 7), over all lengths, an estimate was 

 obtained of the distribution of reproductive conditions among the 



sampled populations (Fig. 35). As noted in the summaries of 

 length and age distributions, the relative distribution of gonad 

 conditions within the combined sex population (males, females, 

 and undetermined) was markedly different from the distributions 

 of male and female populations, due to the large influence of the 

 population of small, immature fish of undetermined sex. In- 

 dividuals of undetermined sex accounted for 55.8% of the overall 

 estimated walleye pollock population. Nonetheless, the combined 

 sex estimates provide the best description of the relative reproduc- 

 tive condition of the sampled population. 



The overall percent frequency distribution (combined sexes) of 

 gonad conditions observed was immature, 77.3%; developing, 

 11.7%; spawning, 6.8%: spent, 2.3%; and inactive, 1.8%. 



Because the walleye pollock population within the study area 

 may have been poorly sampled by the spring 1976 survey (as indi- 

 cated by low estimates of overall population size and low propor- 

 tion of females), the preceding analyses should be considered in- 

 itially as only summaries of the sampled population. The relation 



47 



