322 
Fishery Bulletin 109(3) 
A 
0 
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13 
C 
0 
O 
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a) 
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£ 
374 58 46 63 784 38 40 161 63 78 20 7 
l .1 unidentified 
miscellaneous 
gssKa Cirripedia 
KW1 Larvacea 
mun Thecosomata 
bmadi Copepoda, <2 mm PL 
ISHfiS Copepoda, >2 mm PL 
KSZ3 Reptantia 
LZZ2 Chaetognatha 
ESS Mysidacea 
LJ-lJ Natantia 
tssa Osteichthys 
l'..z.3 other epibenthos 
EX33 Amphipoda. epibenthic 
IXj Amphipoda, pelagic 
BE Euphausiacea.furciliae 
HI Euphausiacea, juv. & adult 
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Shumagin Semidi Kodiak 
Figure 4 
Diet composition for juvenile walleye pollock (Theragra chalcogramma) collected in 
trawl nets in three regions of the western Gulf of Alaska during four seasons (August 
2000-September 2001). Diet is based on taxonomic composition of stomach contents 
by prey count (A) and weight (B). Predator size is indicated by the mean and range 
of standard length (C). Numbers of fish examined are shown along the top of graph 
A. PL=prosomal length. 
> 
Stomach content weight and diet were not strictly 
independent because euphausiids were a principal di- 
etary component. A similar association was inferred off 
Japan when a postwinter rebound in juvenile walleye 
pollock stomach fullness was thought to reflect seasonal 
increase of euphausiid abundance (Yamamura et al., 
2002). Euphausiids are a preferred prey item (Wilson 
et al., 2006) and the large ones especially are a ben- 
eficial dietary addition because their caloric density 
is higher than that of most other prey (Mazur et al., 
2007). However, the consumption of large euphausiids 
may be constrained by fish mouth gape width (Brodeur, 
1998). The constraint relates to body size (Wilson et al., 
2009). Given the negligible overwinter growth, from 
age-0 to age-1 (Brodeur and Wilson, 1996), we hypoth- 
esize that poor wintertime food habits resulted at least 
partly from juvenile walleye pollock being too small to 
consume all sizes of euphausiids. 
The annual cycle of euphausiids in juvenile walleye 
pollock diet likely reflects the predator-prey size rela- 
tionship superimposed on annual cycles of fish growth 
and euphausiid production. In the GOA, euphausiids 
