136 



Fishery Biilletin 88(1). 1990 



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301 



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30 1 



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Julian 

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TIME INTERVAL 



Figure 2 



Cruise periods and time intervals used to analyze the distribution of walleye pollock eggs and larvae in Shelikof Strait. 

 Numljers of tows are shown in blocks indicating cruise times. 



the sampling depth. The percent of eggs that are ex- 

 pected to occur in the depth interval {A,B) is given by: 



P.4,j = (0.06883) • [exp(0.02913-B) 

 - exp(0.02913-A)] 



where P4 g = percent of eggs in depth interval (A,B); 

 A = upper limit of depth interval, >40 m; and B = 

 lower Hmit of depth interval, <250 m. 



We assumed that no eggs occur at depths shallower 

 than 40 m or deeper than 250 m. The adjustment was 

 made by multiplying the catch per 10 m- by the ratio 

 of the theoretical percentage of eggs that occur be- 

 tween 40 m and the bottom depth or 250 m (whichever 

 is shallower) to the theoretical percentage of eggs that 

 occur between 40 m and the maximum tow depth: 



Correction factor 



40, bottom depth or 250 

 "40. tow depth 



In order to compare walleye pollock egg and larval 

 catches at time of maximum abundance in various parts 

 of the western ( lulf of Alaska, we divided the gulf into 

 six strata and examined egg and larval catches for each 

 stratum (P"'ig. 1). For years in which more than one 

 stratum was sampled (and at least three stations were 

 sampled in a stratum), we used catches of eggs during 

 April and catches of larvae from 16 May to 8 June for 

 that year. P^or these cases, we calculated an area- 

 weighted mean abundance (Sette-Ahlstrom method 

 [see Appendix 1]) and percent contribution for each 

 stratum. 



For detailed analysis of the Shelikof Strait area, only 

 those stations from Shelikof Strait to the Shumagin 

 Islands were considered (see Fig. 1). Since the major 

 spawning of walleye pollock in the western Gulf of 

 Alaska occurs in Shelikof Straii in early spring (as we 

 will show later), only cruises conducted in March 

 through early June were considered in the detailed 

 analysis of Shelikof Strait. In order to establish the 



