138 



Fishery Bulletin 88(1). 1990 



ing the density by the total area of the region (Jessen 

 1978). 



N =I.A,,  Ni, 



h 



where A'' = estimate of total abundance, 



Aji = area of region h (in units of 10 ni-) 

 A'';, = mean density in region h (number/ 10 m-) 



^Ah,  N,,, 



A;, , = area of sector i in region /; (in units of 



10 m-) 

 Nil, = mean density in sector / in region h 



(number/10 m-) 



Nfiij = number/10 m- in sample ,/ in sector / in 

 region h. 

 and n.),, = number of samples in sector / in region /;. 



The estimate of variance was adjusted to correct for 

 sectors with one or no sample because a minimum of 

 two samples are required to estimate variance for each 

 sector (see Appendix 3). 



Var A^ = Z .4,,- • Var A^,, 



where 



I A,,,:- Var TV, 



/,,- 



Var A^,, 



A,2 



1 + 



'o 



1+ refers to sectors with at least two 



samples, 

 i„ refers to sectors with one or zero 



samples, 



and 



VariV,,,^ 



Results 



I.(N„,^^-N,,J^ 



("A 



- 1) • n. 



General features of egg and larval distribution 



Season of occurrence Of the 696 tows taken during 

 the surveys from 1972 to 1979, 91 contained walleye 

 pollock eggs and 76 contained larvae (Table 1). Be- 

 tween 28 March and 24 May, 205 tows were taken (29% 

 of the total) and these included 82 and 75% of the tows 

 containing walleye pollock eggs and larvae, respective- 

 ly. A few of the tows taken between October and March 

 also contained eggs, and the 88 tows in June and July 

 accounted for an additional 20% of those containing 

 larvae. From these results it appears that nearly all 

 walleye pollock spawning and the egg and larval period 

 in the Gulf of Alaska occurs in April and May (Table 

 2). Limited numbers of eggs are spawned earlier than 

 this, and some larvae are available to plankton sam- 

 pling after this. 



Among the five time intervals between 12 March and 

 2 June established to investigate occurrences of eggs 

 and larvae in the Shelikof Strait area, the second time 

 interval (29 March to 13 April) accounted for 67% of 

 the eggs, and the third time interval (14 to 29 April) 

 accounted for 66% of the larvae (Table 3). The third 

 time interval accounted for 29% of the eggs, and the 

 fourth and fifth intervals accounted for 17 and \6%i of 

 the larvae, respectively. These results indicate that 

 spawning in Shelikof Strait occurs mainly in early 

 April, and that the larvae resulting from this spawn- 

 ing are present in the area in decreasing numbers into 

 June. 



Areas of occurrence Comparing the catches of wall- 

 eye pollock eggs from April and larvae from 16 May 

 to 8 June from the six strata, H9% of the eggs and 45% 



