Fishery Bulletin 120(1) 
Nursery habitats of flatfish species are a finite space 
in a 2-dimensional environment where density-dependent 
and density-independent factors can contribute to sur- 
vival and recruitment variation (Nash and Geffen, 2012). 
Like juveniles of many other flatfishes, juvenile yellowfin 
sole and northern rock sole reside in coastal waters and 
commonly co-occur throughout their range. The value of 
coastal waters as nursery habitats is frequently enhanced 
through warm temperatures favorable to growth, high 
productivity of prey resources (Wouters and Cabral, 2009), 
and reduced abundances of large predators (Paterson and 
Whitfield, 2000). Of course, the use of these nursery hab- 
itats by multiple species may increase the potential for 
competition. 
Previous work on the feeding habits of shallow-water 
flatfishes in both the GOA and SEBS has revealed diets 
commonly dominated by polychaetes, amphipods, and 
copepods, with bivalves, mysids, and cumaceans being 
important to some species (Holladay and Norcross, 1995; 
Lang et al., 1995; Hurst et al., 2007; Yeung and Yang, 
2017). The amount of dietary overlap among species and 
age classes varies considerably. In the SEBS, diets of yel- 
lowfin sole and northern rock sole have been examined in 
deeper areas (depths >30 m) of the shelf but not in near- 
shore areas along the Alaska Peninsula. 
In this study, we examined the foraging habits ofjuvenile 
yellowfin sole and northern rock sole in nearshore waters 
of the SEBS along the Alaska Peninsula and within the 
Port Moller-Herendeen Bay (PM-HB) system, the largest 
coastal embayment of the SEBS. We focused on functional 
aspects of foraging and associations between diet and hab- 
itat selection that influence competition between these 
important species. The data from this work fill a gap and 
provide a baseline for future examination of the effects of 
climate on foraging patterns of these important flatfishes 
in the SEBS. 
Materials and methods 
Field collections 
The SEBS is bordered on the east by the Alaska main- 
land and on the south by the Alaska Peninsula (Fig. 1). 
The region is characterized as a broad, gradually sloping 
shelf of mixed mud and sand sediments (Hurst, 2016). The 
PM-HB system is the largest inlet on the north side of the 
Alaska Peninsula. The system is a shallow (depths mostly 
<10 m), tidally dominated marine inlet, although the head 
of Herendeen Bay is fjord-like with depths up to 100 m. 
Sampling for juvenile flatfish in Port Moller (in both the 
inner and outer regions, IPM and OPM regions), Heren- 
deen Bay (HB region), and the adjacent coastal waters of 
the Bering Sea (BC region) was carried out in August 2012 
aboard the 13-m chartered FV Bountiful. A total of 75 tows 
were completed by using a beam trawl with a width of 3 m, 
height of 0.78 m, 7-mm mesh body, and 4-mm-mesh codend 
(Abookire and Rose, 2005). Depth of tows ranged from 2 to 
30 m, and tows were conducted during daylight hours. The 
net was towed at 1.5 kt (0.77 m/s) for 5 min at each sampling 
station against the prevailing current. The length of each 
tow was measured by using a global positioning system. 
Juvenile flatfish <125 mm in standard length (SL) were fro- 
zen for laboratory processing. In the field, larger fish were 
identified to species, and their lengths were measured. The 
epibenthic macroinvertebrate fauna at each station was 
described by estimating the catch of crangonid shrimp and 
weighing all other benthic invertebrates in major func- 
tional groups (seastars, hermit crabs, other crabs, anemo- 
nes, sand dollars, urchins, sponges, gastropods, and bivalve 
shells). Additional details on sampling, including catch rate 
at each station, can be found in Hurst (2016). 
Bottom water temperature and salinity were measured 
with a YSI Model 85' instrument (YSI Inc., Yellow Springs, 
OH) at the midpoint of the tow. Surface sediments were 
collected at this location with a Ponar grab and frozen for 
laboratory analysis. For analysis, approximately 15 g of 
sediment was washed through a 62-ym sieve, dried, and 
sorted with a mechanical shaker. Grain size distribution 
was reported as the fractions of silt-clay (<6.25 pm), fine 
sand (62.5—250 pm), medium sand (250-500 ym), coarse 
sand (0.5—2 mm), and gravel (>2 mm). A separate sam- 
ple was dried and burned at 550°C for determination of 
organic content of surface sediments. 
Laboratory examination 
Fish from the field were thawed and blotted dry, and spe- 
cies identifications were confirmed. Standard length (to 
the nearest millimeter) and weight (to the nearest 0.01 g) 
were measured. From fish <100 mm SL, stomachs were 
excised from the esophagus to the pyloric caeca and pre- 
served in 10% buffered formalin for a minimum of 2 weeks 
prior to identification of stomach contents. The stomach 
was opened, and the bolus was extracted, blotted dry, and 
weighed (to the nearest 0.0001 g). The bolus was examined 
under a compound microscope, and prey taxa were identi- 
fied to the lowest possible taxon, with the majority (67%) 
identified to family level. Items from the stomach were 
grouped into categories of identifiable taxa, enumerated, 
blotted dry, and weighed. Stomach fullness of each fish 
was calculated as a percentage of body mass (excluding 
the mass of prey items). 
All identified prey items were associated with their 
AphiaID, which can be found in the World Register of 
Marine Species (WoRMS, available from website, accessed 
July 2015). The AphialID is a searchable, unique, and sta- 
ble identifier that provides taxonomic quality control (Van- 
depitte et al., 2015). Prey items were grouped into 
4 functional habitat categories based on life history char- 
acteristics and habitat occupancy during daylight hours. 
The categories were endobenthic, epibenthic, hyperben- 
thic, and pelagic. The habitat categorization of prey taxa is 
used as an indication of the foraging mode, activity level, 
! Mention of trade names or commercial companies is for identi- 
fication purposes only and does not imply endorsement by the 
National Marine Fisheries Service, NOAA. 
