HUGHES and HIRSCHHORN BIOLOGY OF WALLEYE POLLOCK 



survey, 6-yr-old pollock were dominant. One year 

 later, in the most westward region (Sanak- 

 Unalaska 1974), the prominence of the 1967 year 

 class as 7-vr-olds was apparent during both the 

 May-June and July-August surveys. 



During the May-June and August-September 

 1973 surveys of southeast Kodiak and Shelikof 

 Strait, S-yr-old pollock ( 1970 year class) were dom- 

 inant. The unusual strength of this year class was 

 again noted 2 yr later east of Kodiak as 5-yr-olds 

 during the 1975 Kenai survey. However, recruit- 

 ment of the 1970 year class was not successful west 

 of Kodiak, as shown by the low relative abundance 

 of 3-yr-olds in the Chirikof region in 1973, of 4-yr- 

 olds in the Sanak-Unalaska region in 1974, and of 

 5-yr-olds in the Chirikof region in 1975. 



Maturity and Sex Composition 



Most adult pollock ( >859c ) had spawned prior to 

 our earliest sampling (May). Based upon a subjec- 

 tive evaluation of gonad condition from pollock 

 collected during May, it appeared that prime 

 spawning periods were March and April. Ripe 

 males and females were obtained as late as Au- 

 gust, but these represented <0.1% of samples. 

 Both sexes were fully recruited to the spawning 

 population at age 3. Mature or recently spent age 2 

 males were encountered but represented <59e of 

 that age-group. Mature or spent age 2 females 

 were not encountered; however, minor gonad en- 

 largement was noted. Means of lengths at first 

 maturity in spring surveys were 29-32 cm for 

 males and 30-35 cm for females. 



Our data indicate that sex composition fluc- 

 tuates around 50'+^ at 20-45 cm FL but that 

 females become progressively more dominant 

 with larger size ( Figure 4 ). As will be shown later, 

 the point of major difference in sex ratio (45 cm) is 

 composed primarily of age 4, 5 females and age 5, 6 

 males. 



Length-Weight 



Pollock length-weight data by sex were col- 

 lected during the May-June and August- 

 September surveys of the southeast Kodiak and 

 Shelikof Strait regions in 1973. Data were also 

 collected during the September-October 1973 sur- 

 vey of the Chirikof region. Length-weight rela- 

 tions were determined for these survey regions 

 and periods (Figure 5) by fitting the logarithmic 

 form of the equation (W = aL''). where W is body 



weight in grams and L is fork length in centi- 

 meters, to the mean weight per centimeter-length 

 interval. 



Comparison of these curves indicates that 

 female pollock measuring >33 cm weighed con- 

 siderably less than males of equal length during 

 the May-June postspawning survey. Female 

 weight gain during summer was more rapid than 

 in males, and differences in weight-at-length in 

 the Shelikof Strait, southeast Kodiak, and 

 Chirikof regions were negligible during the 

 August-October sampling. 



Regional differences during spring-summer 

 periods were also noted. Shelikof Strait pollock 

 were heavier than southeast Kodiak pollock of 

 equal length during spring and considerably 

 lighter during summer. This difference may be 

 due to a more rapid weight gain in the southeast 

 Kodiak region or to migration of the most healthy 

 fish out of Shelikof. An additional factor suggest- 

 ing migration was that samples of male pollock in 

 Shelikof actually showed a weight loss from spring 

 to summer. 



Density Distribution and 

 Estimates of Standing Stock 



Pollock were distributed over depth intervals of 

 50-360 m (Table 1). Highest densities occurred at 

 depths of 91-270 m during spring and summer. 

 Geographically, densities were highest at 

 Sanak-Unalaska (181-270 m), followed by south- 

 east Kodiak (91-180 m). Spring-summer 1973 as- 

 sessment surveys of Shelikof Strait and southeast 

 Kodiak indicated highest densities during sum- 

 mer. 



The summer biomass of pollock exceeding 20 cm 

 FL was estimated as 610.000-1,200,000 metric 

 tons (t) of whole fish (Table 1). Regional biomass 

 estimates were greatest in the Chirikof region, 

 followed by Sanak-Unalaska, southeast Kodiak, 

 Kenai, and Shelikof Strait. 



Growth 



Length-age data from the nine surveys were 

 fitted by the von Bertalanffy relation /, = L^ {l - 

 exp k(t-tf^)} following computational procedures 

 by Fabens ( 1965). Because variation in age range 

 affects comparability of parameters (Hirschhorn 

 1974), curve fits over original age ranges were 

 supplemented: 1) with fits over a standardized age 

 range of 2-8 yr, 2 ) with an artificial data point ( 0,0 ) 



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