FISHERY BULLETIN: VOL. 85, NO. 3 



perature steadily decreased from 6.9°C to 6.0°C, 

 and at the bottom (120 m) the temperature 

 dropped to 5.5°C. Among the four XBT casts 

 (taken at 12-h intervals), the temperature at a 

 given depth varied as much as 0.5°C: an isotherm 

 depth varied vertically by as much as 50 m. 



Salinity varied from 31.5 to >33.5%<- in the sur- 

 vey area. Lowest salinities were found at the sur- 

 face toward the Alaska Peninsula, and high salin- 

 ities were found offshore in deeper waters. 

 Isohalines generally sloped from offshore to in- 

 shore. This slope was most pronounced at Section 

 A, the one closest to Shelikof Strait. Most larvae 

 were in water between 31.5 and 32.2%f. The salin- 

 ity profile at the CTD station closest to the diel 

 station showed a slight and steady increase in 

 salinity with depth starting from a surface value 

 of 31.8%(: and ending with a bottom (142 m) value 

 of32.1%o. 



Density sections (ct^) show the same sloping 

 pattern as the salinity sections but are even more 

 pronounced (Fig. 4). Values ranged from <25.0 at 

 the surface near the Alaska Peninsula to >26.4 in 

 deeper waters near the edge of the continental 

 shelf. No sharp pycnocline was observed but 

 rather a gradual increase in density with depth 

 and distance from the Alaska Peninsula. Most 

 walleye pollock larvae were in water with densi- 

 ties between 25.0 and 25.4 a^. The density profile 

 observed near the diel station closely paralleled 

 the salinity profile, with a gradual increase with 

 depth from a, = 24.9 at the surface to ct< = 25.4 at 

 the bottom (142 m). 



Relative Abundance of Eggs 

 and Larvae 



Neuston tows and bongo tows captured eggs of 

 13 and 14 taxa, respectively (Fig. 5). Rank orders 

 of abundance, based on estimated total numbers 

 offish eggs in the neuston catches showed Micro- 

 stomus pacificus (Dover sole) to be in greatest 

 abundance, followed by Glyptocephalus zachirus 

 (rex sole) and Theragra chalcogramma. In bongo 

 catches, unidentified pleuronectid (righteye 

 flounders) eggs were most abundant, followed by 

 those of M. pacificus, G. zachirus, and T. chalco- 

 gramma. 



Larvae of 29 and 42 taxa were identified in 

 neuston and bongo catches. Rank order of abun- 

 dance of fish larvae in neuston tows, based on 

 estimated total numbers, showed Ammodytes 

 hexapterus (Pacific sand lance) to be most abun- 

 dant followed by Hexagrammos decagrammus 



(kelp greenling), Lyconectes aleutensis (dwarf 

 wrymouth), Bathymaster spp. (ronquils), and T. 

 chalcogramma. In bongo catches T. chalco- 

 gramma larvae were most abundant followed by 

 those of Bathymaster spp., A. hexapterus, Hip- 

 poglossoides elassodon (flathead sole), and 

 unidentified gadids (codfishes). 



Distribution and Abundance of 

 Walleye Pollock Eggs and Larvae 



Eggs of walleye pollock were taken in 26% of 

 the bongo tows and in 27% of the neuston tows but 

 in low abundance. Only 262 eggs were collected. 

 Some early stage eggs were collected, indicating 

 recent spawning, but older eggs were also 

 present. Eggs were found mainly in water over 

 the deeper part of Shelikof Strait, with decreasing 

 abundance to the southwest (Fig. 6). 



Larvae of walleye pollock were found in 89% of 

 the bongo catches and 24% of the neuston catches. 

 The center of larval concentration was near the 

 middle of the survey pattern (Fig. 2). Mean stan- 

 dard length of the larvae throughout the survey 

 was 10.63 mm (range 3.8-21.3 mm, SD = 1.81 

 mm), with no differences in mean length by area. 

 At each of five stations near Sutwik Island and 

 the Semidi Islands, more than 1,000 larvae/10 m^ 

 were encountered. At 44 of the 64 stations, more 

 than 100 larvae/10 m^ were found. A total of over 

 10^^ larvae was estimated to be present in the 

 survey area. 



Vertical Distribution of Walleye 

 Pollock Larvae 



In preliminary tows with the 20 cm bongo nets 

 most larvae were caught above 60 m. During the 

 vertical distribution study actual depths of sam- 

 pling based on bathykymograph records covered 

 the ranges of 14-20, 21-28, 28-38, and 39-47 m 

 (Table 2). 



The mean length of the larvae during our diel 

 vertical distribution study was 11.1 mm SL. The 

 range of mean lengths among the individual sam- 

 ples was 10.0-12.2 mm SL, and the range of stand- 

 ard deviations was 0.8-2.3 among hauls with 

 more than 10 larvae. No patterns of size of larvae 

 with depth or time of day were seen by visual 

 inspection of the data, and since the range of 

 mean lengths was so narrow, and the confidence 

 intervals overlapped, no further analysis was per- 

 formed. 



There were no diel differences in catch rates 



506 



