Ferm et al.: Foraging habits and dietary overlap of Limanda aspera and Lepidopsetta polyxystra in the Bering Sea 7 
identified as the primary contributors except that cope- 
pods appeared less important than when expressed in 
PSIRI values (Fig. 4A). Examination of diets by using 
the functional habitat categories of the prey revealed 
that yellowfin sole consumed primarily endobenthic prey 
(%W’=66.0%), predominantly polychaetes with lesser 
amounts of epibenthic and hyperbenthic prey. The diet 
of northern rock sole also included a high proportion of 
endobenthic prey (%#W’=42.5%), but they foraged much 
more extensively on hyperbenthic and pelagic prey (com- 
bined %W’=45.8%), primarily mysids and euphausiids. 
Polychaetes were the dominant prey in all sampling 
regions for both flatfishes (%W’=33.3-65.7%), but there 
were spatial differences in contributions of secondary 
prey types (Fig. 4). For yellowfin sole, copepods were most 
important in the HB region (%W’=27.4%), hydrozoans 
were common in the IPM and OPM regions (%W’~13%), 
and amphipods (%W’=28.0%) and mysids (%W’=12.9%) 
were common in samples collected in the BC region. For 
northern rock sole, copepods were most important in the 
Diet composition (Y%weight) 
K> <1 
SLR 
teacecececes 
Sess d 
= 
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5 
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NRS 
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HB region (%W’=31.9%), and decapods were common in 
the IPM region (%W’=16.5%). Mysids (%W’=20.9%) and 
euphausiids (%W’=26.2%) were most commonly consumed 
in the BC region. Endobenthic prey dominated the diets 
of both species in the IPM and OPM regions, with other 
functional categories making significant contributions in 
other regions. Hyperbenthic and pelagic prey contributed 
the most to diets of yellowfin sole in the HB region and 
northern rock sole in the BC region. 
Yellowfin sole and northern rock sole had low levels of 
dietary overlap across the study area, with an overall SI of 
0.39. This low overlap was in part a result of spatial segre- 
gation because overlap was notably higher (SI=0.55) when 
calculated by using only fish collected at sampling stations 
where the species co-occurred. Within sampling regions, 
dietary overlap was highest in the HB region (SI=0.53) 
and lowest in the OPM region (SI=0.15). 
The low level of dietary overlap does not appear to have 
been driven by differences in body size of yellowfin sole 
and northern rock sole captured in the study area. The 
[ZA Polychaeta 
[—] Amphipoda 
#4) Cnidaria 
Copepoda 
CXN Bivalvia 
[=] Cumacea 
EEE Decapoda 
RA Mysida 
Mim Euphausiacea 
(ZZ) Other 
| (ZZ 
EERE Pelagic 
A S223 Hyperbenthic 
[ZZ] Epibenthic 
mm Endobenthic 
HB 
Figure 4 
Diet composition in percentages by weight based on taxa identified in stomach contents of yellow- 
fin sole (Limanda aspera) (YFS) and northern rock sole (Lepidopsetta polyxystra) (NRS) captured 
in coastal areas of the southeastern Bering Sea in August 2012. The top group of graphs catego- 
rizes prey taxonomically, and the bottom group of graphs categorizes prey by functional habitat. 
Graphs on the right present diets by sampling region in the study area: Bering Sea coastal waters 
(BC), Herendeen Bay (HB), the Outer Port Moller (OPM), and the Inner Port Moller (IPM). 
