KENDALL ET AL.: GROWTH OF LARVAL WALLEYE POLLOCK 



PERCENTAGE OF LARVAE AT EACH DEPTH 



10 



20 



30 



Q. 



Q 



40 



1830 



2230 



Time 

 0230 0630 



1030 



1430 





• 



50 



I I — I — I — I 



• Actual sampling depth q 20 40 



Percent scale 



Figure 7. — Relative abundance as percent of larvae at each depth for each time interval, of walleye 

 pollock larvae from the vertical distribution study, May 1983. 



Comparison of Catches of 



Walleye Pollock Larvae by 



Different Gears 



The sizes of larvae in the different bongo nets at 

 the vertical distribution station were similar 

 (Table 3). Mean lengths of larvae in the 20 cm 

 bongo nets varied from 11.00 in the 333 ixm mesh 

 net to 11.10 mm in the 253 fxm mesh net 

 (SD = 1.76 and 1.69 mm respectively); mean 

 length in the 60 cm bongo nets was 11.07 mm 

 iSD = 1.77 mm). The Tucker trawl, however, 

 caught larvae that had a mean length of 9.64 mm 

 (SD = 1.67 mm). The overall mean abundance of 

 larvae in the 20 cm bongo in the 28-38 m depth 

 stratum nets (11.82 larvae/10 m-^) was similar to 

 that in all the Tucker trawls (11.66 larvae/10 m^) 

 which were towed at 35 m. The mean of the 

 catches in the 60 cm bongo nets, towed just below 

 the deepest 20 cm bongo, was not notably differ- 

 ent from the mean of those 20 cm bongo catches 

 taken at the same times. 



Variations in overall catches in the 20 cm 

 bongo nets at the vertical distribution stations 

 seemed to reflect the patchy nature of the concen- 



tration of larvae and not net avoidance related to 

 time of day. The largest catches occurred during 

 daylight, at 1030 h, while the smallest catches 

 occurred during the time intervals immediately 

 preceding (0630 h) and immediately following 

 (1430 h) the largest catches. Since we sampled 

 one geographic site rather than following a 

 drogue, we probably sampled water with different 

 concentrations of larvae as it drifted past us dur- 

 ing the 48-h sampling. It appears that the larvae 

 decreased from a concentration greater than 

 1 m '^ during the first 24 hours to <0.5 m "^ dur- 

 ing the second 24 hours. The size of larvae did not 

 change during the study again indicating that 

 increased daytime net avoidance was not signifi- 

 cant. 



Hydrography in Relation to 



Distribution of 



Walleye Pollock Larvae 



No obvious hydrographic features were associ- 

 ated with larval distributions. At the diel station, 

 larvae were concentrated between 14 and 47 m 

 where temperature within the upper 50 m was 



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