316 
Regional variation in the annual feeding cycle 
of juvenile walleye pollock 
{Theragra chalcogramma ) 
in the western Gulf of Alaska 
Matthew T. Wilson (contact author ) 1 
Andre Buchheister 2 
Christina Jump 1 
Email address for contact author: matt.wilson@noaa.gov 
1 Alaska Fisheries Science Center 
National Marine Fisheries Service 
National Oceanic and Atmospheric Administration 
7600 Sand Point Way NE 
Seattle, Washington 98115 
2 Department of Fisheries Science 
Virginia Institute of Marine Science 
College of William & Mary 
Gloucester Point, Virginia 23062 
Abstract — Juvenile fish in temper- 
ate coastal oceans exhibit an annual 
cycle of feeding, and within this cycle, 
poor wintertime feeding can reduce 
body growth, condition, and perhaps 
survival, especially in food-poor areas. 
We examined the stomach contents 
of juvenile walleye pollock ( Theragra 
chalcogramma) to explain previously 
observed seasonal and regional 
variation in juvenile body condition. 
Juvenile walleye pollock (1732 fish, 
37-250 mm standard length) of the 
2000 year class were collected from 
three regions in the Gulf of Alaska 
(Kodiak, Semidi, and Shumagin) rep- 
resenting an area of the continental 
shelf of ca. 100,000 km 2 during four 
seasons (August 2000 to September 
2001). Mean stomach content weight 
(SCW, 0.72% somatic body weight) 
decreased with fish body length 
except from winter to summer 2001. 
Euphausiids composed 61% of SCW 
and were the main determinant of 
seasonal change in the diets of fish 
in the Kodiak and Semidi regions. 
Before and during winter, SCW and 
the euphausiid dietary component 
were highest in the Kodiak region. 
Bioenergetics modeling indicated a 
relatively high growth rate for Kodiak 
juveniles during winter (0.33 mm 
standard length/d). After winter, 
Shumagin juveniles had relatively 
high SCW and, unlike the Kodiak and 
Semidi juveniles, exhibited no reduc- 
tion in the euphausiid dietary compo- 
nent. These patterns explain previous 
seasonal and regional differences in 
body condition. We hypothesize that 
high-quality feeding locations (and 
perhaps nursery areas) shift season- 
ally in response to the availability of 
euphausiids. 
Manuscript submitted 11 January 2011. 
Manuscript accepted 13 May 2011. 
Fish. Bull. 109:316-326 (2011). 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
In temperate and subpolar oceans, 
many coastal fishes exhibit an annual 
cycle in feeding due to seasonal 
changes in prey availability and com- 
position (Wootton, 1998). The cyclical 
low point in feeding conditions often 
occurs during winter when environ- 
mental conditions can adversely affect 
growth and survival of juveniles and 
thereby constrain year-class strength 
(Sogard, 1997; Hurst, 2007). How- 
ever, juveniles that inhabit prey-rich 
areas may fare better than those in 
prey-poor areas because of enhanced 
accumulations of body reserves before 
winter, acquisition of energy during 
winter, or both. Thus, prey-rich areas 
may support relatively high growth 
and survival and thereby function as 
important nurseries for the production 
of recruits (Dahlgren et al., 2006). 
Walleye pollock ( Theragra chal- 
cogramma) is prominent in many 
North Pacific ecosystems as a major 
food web component and fishery re- 
source (Springer, 1992). In the Gulf 
of Alaska (GOA), juvenile walleye pol- 
lock are one of the most abundant 
neritic forage fishes and are con- 
sumed by seabirds, fishes, and ma- 
rine mammals (Brodeur and Bailey, 
1996). Predation-related mortality of 
juveniles can significantly determine 
walleye pollock year-class strength 
in the GOA (Bailey, 2000). Because 
juveniles require food to grow, and 
mortality can decrease with body 
size (Sogard, 1997), description of the 
annual feeding cycle will provide a 
trophic context for annual cycles in 
growth (Brodeur and Wilson, 1996) 
and mortality (e.g., Hurst, 2007). 
F urthermore, year after year, specific 
regions of the GOA support juvenile 
walleye pollock that are larger (Wil- 
son, 2000; Wilson et al., 2009) and in 
better body condition (Buchheister et 
al., 2006) than members of the same 
year class from other regions, thus 
raising the possibility that seasonal 
changes in habitat quality (e.g., food 
resources) vary geographically. 
In the GOA, the principal habitat 
of juvenile walleye pollock occurs 
from Kodiak Island to Unimak Pass 
(Brodeur and Wilson, 1996) (Fig. 1). 
Young-of-the-year (age-0) juveniles 
are particularly abundant in the 
Semidi Bank region because of down- 
stream advection of larvae produced 
by the large spawning aggregation 
that forms during early spring in 
Shelikof Strait (Hinckley et al., 1991). 
During winter, growth of age-0 juve- 
niles decreases to a negligible rate 
when epibenthic foraging supplements 
the acquisition of pelagic prey (Bro- 
deur and Wilson, 1996). In addition, 
