KENDALL ET AL.: GROWTH OF LARVAL WALLEYE POLLOCK 



area of sea surface represented by that station 

 (the Sette-Ahlstrom method, see Smith and 

 Richardson 1977). This estimate was thought to 

 make best use of all the available data. 



A chi-square test analyzed differences in the 

 numbers of walleye pollock larvae caught as a 

 function of time of day and depth at the diel sta- 

 tion. For this test, numbers of larvae in the two 

 sides of the 20 cm bongo nets were combined. 

 Also, catches at the same time and depth but on 

 different days were combined when complete 

 depth series were collected. Four out of six times 

 two complete depth series were collected; at two 

 times only one complete depth series was col- 

 lected. 



Zooplankton were sorted, identified, and enu- 

 merated from subsamples of collections made 

 with the 253 ixm mesh net. The subsample was 

 chosen such that at least 500 organisms were 

 sorted from each sample. 



For larval feeding analysis, 20 walleye pollock 

 larvae (or the total sample when <20 were 

 caught) were selected to represent the size range 

 in the total sample from each of the 333 fxm mesh, 

 20 cm bongo net samples. The guts were dissected 

 from the larvae, and all food items in the foregut, 

 midgut, and hindgut were teased out, identified, 

 and counted. 



Lengths and greatest widths were measured for 

 all food items in the larvae collected at 0630, 29 

 May. Lengths used were carapace length for cope- 

 pod nauplii, metasome length for copepodids, and 

 total length for all other prey. These measure- 

 ments were used to estimate volumes of prey or- 

 ganisms, which were applied to the rest of the 

 samples. Mensuration formulae were used to cal- 



culate the volume of copepod eggs, copepod nau- 

 plii, copepodids of Pseudocalanus spp., Acartia 

 spp., and Oithona spp. (Nishiyama and Hirano 

 1983; Table 1). Pseudocalanus spp. mensuration 

 formulae were used to estimate the volumes of 

 unidentified copepodids. The volumes of other 

 food items were not estimated since their low 

 abundance did not allow adequate measurement 

 of body proportions. 



Samples used for age and growth analysis were 

 selected from one station within the area of 

 highest larval density (Station 37, Fig. 2), and 

 from four stations located outside of this dense 

 patch. Standard lengths of larvae from as broad a 

 size range as possible within each sample were 

 measured to the nearest 0.1 mm using an ocular 

 micrometer. Both sagittal otoliths were removed 

 and cleaned using a pair of fine needles under a 

 dissecting microscope fitted with polarizing fil- 

 ters. Whole otoliths were affixed to microscope 

 slides with clear histological mounting medium 

 and increments read in the sagittal plane under a 

 compound microscope with transmitted light at 

 1000 X magnification. Most of the otoliths had a 

 distinct distal-proximal curvature and readabil- 

 ity was enhanced when the otolith was mounted 

 with the concave side up. 



Increments were identified as a pair of adjacent 

 light and dark bands, formed concentrically 

 around the focus. A prominent dark band sur- 

 rounding the focus was observed on each otolith 

 (Fig. 3). Since mean otolith diameter at this band 

 (16.0 ± 0.13 |jLm SE) was similar to the diameter 

 of otoliths from 1-day-old, laboratory-reared lar- 

 val pollock (18.97 ± 0.37 ^JLm, Nishimura and Ya- 

 mada 1984; 16-20 jxm, Walline 1983; 15.3 ± 1.2 



Table 1. — Mensuration formulae (Nishiyama and Hirano 1983),^ length to width 

 ratios, metasome to whole body ratios, metasomal lengths, mean lengths, and 

 mean diameters used to calculate volumes of copepodids, copepod nauplii, and 

 copepod eggs in guts of larval walleye pollock in Shelikof Strait. 



'Mensuration formulae (Nishiyama and Hirano 1983): 

 Volume of copepodids = [Lm/6(Lm/K)2TT]/m. 



Volume of copepod nauplii = (^ carapace length^ j; 



mean carapace length = 0.187. 

 Volume of copepod eggs = (? egg diameters J; 



mean egg diameter = 0.1 10. 



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