Wilson et al.: Regional variation in the feeding cycle of juvenile Theragra chalcogramma 
321 
Table 2 
Prey groups recovered from the stomach contents of juvenile walleye pollock (Theragra chalcogramma) collected during August 
2000 to September 2001 by trawling in the western Gulf of Alaska. Diet composition is characterized by percent frequency of 
occurrence (%FO), percent of total prey count (%No), and percent of total prey weight (%W). Weight (mg) per individual prey item 
(W per item) indicates relative prey size. 
Prey group 
%FO 
%No 
%W 
W per item 1 
Amphipoda, epibenthic 
6.7 
0.47 
0.86 
4.57 
Amphipoda, pelagic 
8.8 
0.43 
0.42 
2.37 
Cirripedia larvae 
5.7 
1.72 
0.07 
0.08 
Copepoda, <2 mm PL 
56.4 
44.59 
2.30 
0.11 
Copepoda, >2 mm PL 
42.4 
14.04 
5.84 
0.76 
Chaetognatha 
12.5 
0.55 
1.93 
9.54 
Euphausiacea furciliae 
10.0 
1.85 
0.58 
0.25 
Euphausiacea juveniles and adults 
49.6 
7.53 
61.32 
19.91 
Larvacea 
32.7 
17.24 
0.96 
0.12 
Mysidacea 
0.9 
0.03 
0.24 
14.52 
Natantia 
2.1 
0.06 
1.13 
65.09 
Osteichthyes 
4.3 
0.10 
14.35 
626.48 
Reptantia 
20.4 
1.04 
2.24 
5.77 
Thecosomata 
21.3 
6.94 
0.85 
0.16 
miscellaneous prey (e.g., Ostracoda) 
3.7 
0.31 
0.05 
0.12 
hard items (e.g., sand) 
0.9 
0.00 
0.18 
2.70 
other epibenthic prey (e.g., Cumacea, harpacticoids) 
5.1 
2.06 
3.35 
1.92 
parasites (e.g., Nematoda) 
10.4 
0.33 
0.68 
3.62 
unidentified prey 
45.4 
0.71 
2.65 
0.15 
Groups combined 
100 
100 
100 
2.72 
1 Per item weight (W/No.) was computed with only items that were <50% digested 
estimated for only the six remaining season-region 
combinations. 
Absolute growth rate (mm SL/d) generally increased 
with seasonal progression, except during WinOl when 
growth in the Shumagin region was negative. Com- 
pared to the growth of Kodiak fish, the negative 
growth of Shumagin fish was associated with rela- 
tively small-fish body weight, low daily ration, and 
an energy-poor diet. In terms of specific growth rate, 
the negative wintertime growth equates to a daily 
loss of 1% BW for Shumagin juveniles; in contrast, 
the positive wintertime growth of the Kodiak juveniles 
equates to a daily gain of 1% BW. It therefore appears 
that the higher daily ration and energy-rich diet ob- 
served among juveniles in the Kodiak region during 
WinOl resulted in a relatively high season-specific 
growth rate. 
Discussion 
Our results show that members of the largest popu- 
lation of juvenile walleye pollock in the GOA exhibit 
seasonal fluctuations in stomach content weight simi- 
lar to those of other cold-water fishes (Wootton, 1998). 
Because these were growing juveniles, the feeding 
cycle was superimposed on marked increases in fish 
body size. Body size is an important consideration 
because increases in body size generally correspond 
with decreases in the specific weight of stomach con- 
tents (Wootton, 1998). Thus, the late summer-to-winter 
and the summer-to-late summer declines in %BW 
can be at least partly explained by increasing fish 
length. However, a length effect does not explain the 
winter-to-summer rebound in stomach content weight, 
which might alternatively be explained by a postwin- 
ter rebound from relatively poor wintertime feeding 
conditions. We acknowledge that the Kodiak region in 
particular was represented by few fish, which increases 
uncertainty in our observations, but the seasonal pat- 
tern was similar among regions and was consistent 
with a postwinter recovery in body condition (Buch- 
heister et al., 2006) and acceleration in growth rate 
(Wilson et al., in press). The increase in water tem- 
perature from winter to summer may have stimulated 
feeding by increasing gastric evacuation and systemic 
demand (Wootton, 1998). Another contributing factor 
might have been prey availability. Zooplankton popula- 
tion density in the GOA increases during spring owing 
to an early summer peak in copepod abundance before 
declining from summer to winter (Coyle and Pinchuk, 
2003). Prey availability was thought to influence posi- 
tively stomach content weights of walleye pollock in the 
Bering Sea (Dwyer et al., 1987). 
