Wilson et al.: Geographic variation among age-0 Theragra chalcogramma 



215 



Chiniak Bay 

 Ugak Bay 

 Kiliuda Bay 

 Shelf 



n~~ 1 1 r^ r~ 



21 Mar 10 Apr 30 Apr 20 May 9 Jun 29 Jun 



Hatching date during 1993 



Figure 6 



Hatching-date composition of age-0 walleye pollock (Theragra 

 chalcogramma) by area from samples collected near Kodiak 

 Island, 5-18 September 1993. 



in other words, we did not know where they had been 

 prior to capture. 



As evidenced by geographic variation in hatching-date 

 distributions, cohort-specific differences persisted well 

 into the juvenile stage and had important implications 

 for inter-cohort differences in survival. The median 

 hatching dates of fish in bays were similar to those es- 

 timated for north Kodiak Island by Brown and Bailey 

 (1992). In contrast, fish over the shelf had substantially 

 later hatching dates. There is little evidence of pollock 

 spawning within our study area; therefore it seems 

 likely that the differences in hatching dates reflect suc- 

 cessive immigration of sequential cohorts. However, the 

 presence of the youngest cohort, fish hatched during 



-2 



-1 5 



-1.0 -0 5 0.5 10 1.5 



E 



CO 



B 



15 



1 



05 1 



0.0 

 -0.5 

 -1.0 -I 

 -1 5 



stress=9.79 

 r 2 =0.87 



V 



O 

 O 



-15 -10 -0.5 5 



NMS dimension 1 



1 



Figure 7 



Nonmetric multidimensional scaling (NMS) of 

 samples based on age-0 walleye pollock (Theragra 

 chalcogramma) diet composition (A), or zooplankton 

 composition (B). Symbols indicate four different 

 sampling areas. For diet, the small (<66 mm SL) 

 fish in bays are represented by filled symbols. 



