Fishery Bulletin 120(1) 
(Fig. 2). Sampling coverage for each predator species was 
above 90%, indicating a robust description of prey diver- 
sity within the diets of yellowfin sole (93.7% [SE 1.9]) and 
of northern rock sole (97.1% [SE 0.8]) (Fig. 2). 
Diet composition 
Copepods, polychaetes, amphipods, and mysids were most 
important in the diets of both flatfish species (on the basis 
of PSIRD (Table 1; for complete diet composition with all 
prey taxa identified from stomach contents, see Supple- 
mentary Table [online only]). Copepods were the dominant 
prey category for both northern rock sole and yellowfin 
sole, with PSIRI values of 31.4% and 32.6%, respectively. 
Within the copepod group, an epibenthic harpacticoid, 
Ectinosoma sp., was the most important prey item for both 
species, with yellowfin sole also consuming significant 
amounts of hyperbenthic Eurytemora herdmandi. Poly- 
chaetes were the next most important prey group for both 
species with PSIRI values of 29.3% for yellowfin sole and 
19.1% for northern rock sole. Although most polychaetes 
could not be identified to family or genus, of those iden- 
tified, the family Ampharetidae was the greatest contrib- 
utor to the diets of both species. Amphipods had PSIRI 
values of 18.6% for yellowfin sole and 15.5% for northern 
rock sole. Yellowfin sole consumed a diversity of amphipod 
species, but amphipod consumption by northern rock sole 
was dominated by Liljeborgia spp., Metaphoxus spp., and 
Photis spp. Mysids had a PSIRI of 16.0% for northern rock 
sole but had a PSIRI of only 4.8% for yellowfin sole. 
The prey category that differed the most between the 
diets of the 2 flatfish species was euphausiids, which were 
rare in the diets of yellowfin sole (PSIRI=0.8%) but com- 
mon in the diets of northern rock sole (PSIRI=11.1%). 
Thysanoessa raschii accounted for the majority of euphau- 
siids consumed by northern rock sole. 
When diet composition was expressed in percentage 
by weight (%W’) of prey types, the same groups were 
Table 1 
Prey-specific index of relative importance (PSIRI) of the taxa of primary prey found in stomach contents of yellowfin sole 
(Limanda aspera) (YFS) and northern rock sole (Lepidopsetta polyxystra) (NRS) sampled in coastal areas of the southeastern 
Bering Sea in August 2012. Values for the 4 primary groups, Amphipoda, Copepoda, Mysidae, and Polychaeta, in the diets of 
sampled fish are presented, with additional details at a higher taxonomic resolution. Values are provided only for prey groups 
with PSIRI values >0.01. For complete diet composition with all prey taxa identified from stomach contents, see Supplementary 
Table (online only). BL=body length. 
Taxonomic groups 
Prey group Prey taxa 
AMPHIPODA 
Atylus collingi 
Caprella spp. 
Caprellidae <4 mm BL 
Caprellidae >4 mm BL 
Dyopedos unispinus 
Eohaustorius spp. 
Gammaridea 
Gammaropsis spp. 
Decapoda Ischyroceridae 
Euphausiacea Ischyrocerus spp. 
Pisces ; I Liljeborgia spp. 
Gastropoda Lysianassidae 
Isopoda Metaphoxus spp. 
Mysida Orchomene spp. 
Nematoda Orchomenella spp. 
Ostracoda Pacifoculodes zernovi 
Plantae Photis macinerneyt 
Polychaeta Photis spp. 
Tunicata 
Other Ramellogammarus 
vancouverensis 
Wecomedon similis 
Unidentified Amphipoda 
Amphipoda 
Arthropoda 
Bivalvia 
Bryozoa 
Cirripedia 
Cnidaria 
Copepoda 
Crustacea 
Cumacea 
Podoceropsis chionocetophilia 
Breakdown of taxa in primary groups 
Prey taxa 
COPEPODA 
Ectinosoma spp. 
Ectinosomatidae 
Eurytemora herdmandi 
Oithona spp. 
Stephos spp. 
Tigriopus spp. 
Tisbe spp. 
Zaus spp. 
MYSIDAE 
Mysidae, juvenile/adult 
Mysidae, larvae 
Neomysis kadiakensis 
Pacifiacanthomysis 
nephrophthalma 
Xenacanthomysis 
pseudomacropsis 
POLYCHAETA 
Ampharetidae 
Maldanidae 
Nereididae 
Onuphidae 
Phyllodocidae 
Spionidae 
Terebellidae 
Unidentified Polychaeta 
