148 



Fishery Bulletin 88(1), 1990 



, n 1 1 . . I . ' ' .1  ' . I . . I . . .I . . I . .-I- 



I I I I I I I I ' 



I  I   I  ' I '  I 



Figure 10 



('entrriiiJs of tlirt-t' ccjhnrts of walleye piillock 

 egg and larval distributions in Shelikof 

 Strait. Labels beside dots indicate stage (egg) 

 i>r length increment, with time interval in 

 parentheses. 



Discussion 



As we compiled data for analysis, we made several 

 assumptions which may have affected our results. Most 

 of the tows used to describe egg distributions did not 

 exceed a maximum depth of 20(1 m and, therefore, a 

 correction factor was applied to account for eggs in 

 deeper parts of the water column. Our key assumption 

 for this correction was that the depth distribution of 

 eggs found in Shelikof Strait in 1985 and 1986 was ap- 

 plicable throughout the study area and for all years ex- 

 amined. The validity of this assumption needs to be 

 verified by determining geographic and interannual 

 variability in depth distribution and bouyancy of eggs. 

 Specific gravity and depth distribution of the eggs 

 change with development (Kendall and Kim 1989), but 

 these changes were not accounted for in our analysis. 

 In many of the analyses, there was an implicit as- 

 sumption that samples were drawn randomly from 

 within a sector or stratum. Some of what appears to 



be random variability in the data may be features of 

 distribution on a scale too fine for our analyses. In com- 

 l)ining data from various years with slightly different 

 sampling times and station patterns, small-scale inter- 

 annual differences may have been blended. Effects of 

 different sampling intensities among the years may 

 have interacted with changes in overall abundance of 

 eggs and larvae, so that patterns in low adundance 

 years may have been overwhelmed by patterns from 

 high abundance years. However, aside from the un- 

 usual spatial distribution of larvae in 1985, and the 

 large size of larvae in late May lif8.3, timing and geo- 

 graphic areas of occurrence of eggs and larvae seemed 

 (juite consistent among years. 



Knowledge of the distribution of eggs and larvae of 

 walleye pollock in the Gulf of Alaska has increased 

 dramatically in recent years. The larvae could not be 

 separated from those of Pacific cod Gadus macroceipha- 

 lus prior to studies of Matarese et al. (1981). Kendall 

 and Dunn (1985) summarized knowledge of ichthyo- 



