KENDALL ET AL.: GROWTH OF LARVAL WALLEYE POLLOCK 



tions. Copepod nauplii 90-600 |xm in length and 

 between 40 and 250 jxm in width were the most 

 abundant food item for larvae <14.0 mm (Fig. 9). 

 The length- and width-frequency distributions of 

 nauplii indicate that Pseudocalanus spp. and 

 Oithona spp. are the likely prey taxa. Nauplii 

 became numerically less important in diets of 

 larger larvae. Pseudocalanus spp. copepodids, 

 copepod eggs, and Oithona spp. copepodids made 

 up a larger numerical portion of the food of these 

 larger larvae (Fig. 10). The increased importance 

 of Pseudocalanus spp. copepodids in the diet of 

 larger larvae is evident in terms of gut volume 

 (Fig. 10). Examination of the contribution of the 

 copepod eggs to the diet indicates that while eggs 

 increase numerically from 1.5% in the 8.0-8.9 mm 

 size group to 55% in the 14.0-14.9 mm size group, 

 their volume increases only from 0.5 to 3.6%. 



The number of food organisms and mean prey 

 volume per larva show a diel feeding pattern (Fig. 

 11). The maximum gut contents were observed 

 during the afternoon. Collections at 2235, 0230, 

 0238, and 0629 have the lowest mean number of 

 food items per larva, which suggests that feeding 

 during darkness is reduced. The mean gut vol- 

 umes show a similar pattern (Fig. 11). Although 

 gut volume at 1047 h on 29 May was unusually 

 low, it was not an indication of reduced feeding. 

 Here the gut contents consisted of numerous cope- 

 pod nauplii and few adult copepods. Thus the cal- 

 culated prey volume is quite low, while the num- 

 ber of food items per gut is high. 



Zooplankton Composition 



Thirty-nine groups of zooplankters were identi- 



500 



400 



300 



200 



100 



I r I I 



_1_ 



_1_ 



N = 1191 



700 



500 



300 



100 



80-110 120-150 160-190 200-230 240-270 280-310 320-350 360-600 



Length of nauplii (/jm) 



B 



_L 



N= 1181 



30-50 60-80 90-110 120-140 150-170 180-200 210-230 240-260 



Width of nauplii (*jnn) 



Figure 9.— Length (Al and width (B) size-frequency distribution of 

 copepod nauplii from guts of walleye pollock larvae. 



511 



