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



211 



Salinity (psu) 

 30 31 32 33 34 30 31 32 33 34 30 31 32 33 34 30 31 32 33 34 



8 10 12 



Chiniak Bay 



8 10 12 4 6 8 10 12 4 6 8 10 12 

 Temperature (°C) 



Figure 2 



Water salinity and temperature profiles obtained in 10 casts at locations where 

 age-0 walleye pollock {Theragra chalcogramma) were collected near Kodiak 

 Island, Alaska, during 5-18 September 1993. 



(ANOSIM, PRIMER, Clarke and Warwick, 2001) ap- 

 plied to the Bray-Curtis similarity matrices. 



Results 



Overall, salinity ranged from 30.3 to 33.0 ppt, and water 

 temperature ranged from 4.4 to 11.3°C (Fig. 2). Shal- 

 low surface layers of relatively fresh water were evident 

 from low near-surface salinities in Ugak Bay and in the 

 inner part of Kiliuda Bay. This part of Kiliuda Bay was 

 also well stratified thermally. Unfortunately, it was not 

 possible to include inner Kiliuda Bay as a fifth area in 

 subsequent statistical analyses because of insufficient 

 sampling. Thermal stratification was also evident at 

 shelf sampling locations. 



A total of 5284 age-0 pollock were collected in 25 

 of the 32 successful trawl hauls (Table 1). These fish 

 were absent only at the four most-offshore locations 

 over Albatross Bank and Chiniak Gully (Fig. 3 1. In ad- 

 dition, no age-0 pollock were caught in shallow (<35-m 

 depth) tows at locations on Albatross Bank; a dense 

 and expansive school of capelin (Mallotus villosus) may 

 have displaced them downward. Median age-0 density 

 was 0.0006 fish/m 3 ; the maximum (0.095 fish/m 3 ) was 

 found in Ugak Bay. 



Standard lengths of 2119 age-0 pollock ranged from 

 25 to 121 mm SL (Table 1, Fig. 4). The fish in Chiniak 

 Bay (91 mm SL), Ugak Bay (90 mm SL), and Kiliuda 

 Bay (89 mm SL) all had a median SL that were larger 



than the median length of fish collected over the shelf 

 (71 mm SL). A surprising number of individuals <50 

 mm SL were collected in Ugak Bay and inner Kiliuda 

 Bay. 



Body condition, based on the reduced, common-slope 

 ANCOVA model, varied among the four areas (Table 2). 

 Because of this effect, area-specific equations were used 

 to describe the length-weight relationship (Table 3, 

 Fig. 5A). After accounting for differences in length, we 

 found that fish from the shelf weighed less than the 

 individuals collected in Chiniak Bay and Ugak Bay. 

 Individuals from Kiliuda Bay were intermediate in 

 weight, differing only from the Ugak Bay fish (Table 

 4). Similar conclusions from the somatic-weight data of 

 fish used in the diet examinations indicated that gut- 

 content weight was not responsible for the relatively low 

 length-specific weights of fish from Kiliuda Bay and the 

 shelf (Tables 2 and 4). 



The fish age-length relationship also varied by area. 

 The relationship was described by using a reduced, 

 common-slope model (Table 2). The common slope was 

 0.78 mm/d (Table 3, Fig. 5B). Differences in line eleva- 

 tion, or age-specific length, indicated that fish from 

 the shelf grew more slowly during the hatch-to-capture 

 period than did the fish from Chiniak or Kiliuda bays 

 (Table 4). Applying these equations to the length data 

 resulted in hatching-date distributions that ranged 

 from mid March to mid July (Fig.6). The fish collected 

 in Chiniak Bay (17 April), Kiliuda Bay (20 April), and 

 Ugak Bay (25 April) all had earlier median hatching 



