582 



Fishery Bulletin 92(3). 1994 



the upper 100 m did not differ by more than 0.5°C 

 between RES 2.5 and GAK 1, the temperature dif- 

 ference in May was almost 1.5°C. 



The water column was nearly isohaline in April: 

 salinity increased approximately 1.5 psu (practical 

 salinity unit) from surface to bottom. Salinity pro- 

 files in May show a well-developed low salinity sur- 

 face layer at four of the stations (Fig. 2), resulting 

 from river runoff and snow melt. The surface salini- 

 ties were 2 to 4 psu lower than in April. However, at 

 RES 2.5 and GAK 1 the freshwater lens was much 

 less developed than at the other stations. The sur- 

 face layer salinity was above 31 psu and almost iden- 

 tical at both stations. Below the halocline, salinities 

 were very similar at all stations. 



Distribution and abundance 



In early May, walleye pollock larvae were caught at 

 all stations and sampled at all depths. A total of 

 16,950 pollock larvae were collected in 39 tows at 

 depths between 7 and 280 m. Larval densities ranged 

 from 0.03 larvaem -3 (RES 4, 105 m) to a maximum 

 of 11.9 larvaem -3 (RES 4, 26 m). Larvae were gener- 

 ally concentrated in the upper 70 m (Fig. 3). Maxi- 

 mum densities occurred at depths between 18 and 



30 m at all stations, except GAK 1, and ranged from 

 2.2 larvae-m -3 to 11.9 larvae-m -3 . Pollock larvae were 

 distributed deeper in the water column outside the 

 sill, at stations RES 4 and GAK 1, than at stations 

 inside the sill (Fig. 3). 



Between May and June, larval densities decreased 

 by two orders of magnitude and ranged from to 0.4 

 larvae-m -3 in early June (Fig. 4). In June, a total of 

 420 walleye pollock larvae were collected in 45 tows 

 at depths between 5 and 250 m. Only tows above 75 

 m caught pollock larvae. Vertically, the maximum in 

 larval density occurred between 10 m (RES 1) and 

 58 m (RES 3). The vertical distribution in early June 

 showed no apparent pattern in relation to station 

 location (Fig. 4). 



Using vertical distribution profiles, we estimated 

 larval abundance at each station. In May, estimated 

 abundances ranged from 60 larvaem -2 at RES 1 to 

 575 larvaem -2 at GAK 1 (Table 1). Abundances at 

 the outer stations were much higher than in the in- 

 ner basin owing to high larval densities below 50 m 

 at RES 4 and GAK 1. 



In June abundances ranged from 0.5 larvae-m -2 

 at RES 1 to 10.3 larvaem -2 at RES 3. The estimated 

 abundances were again higher at the outer stations. 

 The highest abundance was found above the sill, as 



(V 

 Q 





■.ni.i 



ISO 



£ 



RES 1 



RES 3 



RES 2 



RES 25 



8 12 



RES 4 



GAK 1 



Abundance (number/m 3 ) 



Figure 3 



Vertical distribution of walleye pollock larvae, Theragra chalcogramma, in Res- 

 urrection Bay, Alaska, 1-4 May 1989. 



