FISHERY BULLETIN VOL 77, NO 1 



tailed examination, and the above sampling and 

 analytical procedures would average this 

 phenomenon if it does occur. 



Data presented indicate that at least 87'^ of the 

 pollock resource resides at depths 91-270 m during 

 the summer with greater bathymetric disperse- 

 ment during the spring. Densities were lowest in 

 the Kenai region (eastern extreme) and highest in 

 the Sanak-Unalaska region (western extreme). 

 Except for the Kenai and Shelikof regions, where 

 densities were notably low relative to other re- 

 gions, regional biomass estimates are a function of 

 both pollock density and available shelf or slope 

 area at depths of 91-270 m. 



Age and size composition data indicated that 

 strong variations in year-class strength occur and 

 recruitment of year classes is not uniform over the 

 western Gulf. Whereas such geographic varia- 

 tions in year-class strength could be caused by 

 environmental conditions, neither of two promi- 

 nent year classes ( 1967 and 1970) indicated simi- 

 lar relative abundance over the entire east-west 

 range of these surveys. Rather, the 1967 year class 

 appeared in high density only west of southeast 

 Kodiak and the 1970 year class, only at southeast 

 Kodiak and eastward. These geographic density 

 differences were accompanied by observed growth 

 differences (size at age) and by negative depar- 

 tures of observed size at age in these year classes 

 from expected size based on growth curve fits (Fig- 

 ure 7). 



Analysis of all the growth information from 

 these surveys indicated an inverse relation of 

 growth completion rate (A') to relative year-class 

 strength as well as to final estimated fish length 

 (L,). From the differences in K values obtained 

 and assuming M = K, it is inferred that optimally 

 timed harvests per unit input would be larger in 

 low-A' cohorts than in high-/f cohorts. Optimal 

 timing from the yield standpoint also implies en- 

 hancement of the reproductive potential of low-A' 

 cohorts. 



In conclusion, the western Gulf of Alaska pol- 

 lock stock has been described and biological 

 parameters reported for management. It is 



suggested that an east-west separation of spawn- 

 ing stocks may occur near Kodiak and that man- 

 agement should be applied accordingly. 



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