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the north site where fish condition was highest. Zoo- 
plankton biomass and feeding conditions before our 
study likely contributed to the observed differences in 
fish condition. 
In this study the types of prey consumed by juvenile 
POP were very similar between the two areas, and 
large calanoid copepods comprised the majority of ju- 
venile POP diets of all size classes examined. In fact, 
the types of prey consumed by juvenile POP varied 
more by size class of POP than by area. Medium and 
large juvenile POP consumed more larger prey, such 
as euphausiids, than the small juvenile POP. These 
findings are very similar to those found for juvenile 
POP in southeast Alaska (Carlson and Haight, 1976). 
We did not quantify juvenile POP prey to the species 
level; however, the type of large copepods (Euchaeta 
B 
Figure 6 
(A) Average zooplankton biomass (mL/m 3 ), and (B) numeri- 
cal proportion of main zooplankton taxa as sampled with a 
ring net at the north (N) and south (S) Samalga Island sites 
in August. Standard error bars are shown for zooplankton 
biomass and the asterisk indicates a significant difference. 
Main zooplankton taxa included hyperiid amphipods, small 
copepods (<2.5 mm) and large copepods (>2.5 mm). The 
“other” category comprises zooplankton taxa that individu- 
ally represented less than 5% of the numerical proportion 
of the zooplankton samples. 
elongata, Calanus marshallae, Neocalanus cristatus, 
and Metridia sppj and euphausiids ( Thysanoessa ra- 
schii) in the zooplankton samples did not appear to 
differ between sites, indicating that the variety of 
prey species available to juvenile POP was similar 
between sites. 
Water temperature and water column stratification 
are other factors that may affect fish condition. Bot- 
tom water temperatures were similar at both sites in 
August (5.4-5.6°C); however, the water column was 
more mixed at the north site and stratified at the 
south site. Water column stratification determines, in 
part, the amount of primary and, hence, secondary 
productivity by controlling nutrient flow from deeper 
waters. Previous studies have shown that the area 
north of Samalga Pass is an area of upwelling and 
high zooplankton biomass (Swift and Aagaard, 
1976; Coyle 2005) and can be characterized as 
a more productive area than the south site. The 
higher production at the north site may lead to a 
higher zooplankton biomass, which we observed in 
this study, and higher zooplankton lipid stores and 
energy content, potentially benefitting predators 
such as juvenile POP. 
In summary, we have shown that juvenile POP 
condition and abundance vary significantly be- 
tween areas, whereas juvenile POP diet varies by 
size class of this species. Juvenile POP condition 
was higher in the area with lower juvenile POP 
abundance. The differences in fish condition may 
be due to limitation in the quantity or quality of 
available prey. In order to delineate essential fish 
habitat for demersal marine fish species, therefore, 
one must consider not only the presence or absence 
of an organism and its benthic habitat, but also 
the important ecological features of the pelagic 
habitat. 
Acknowledgments 
We sincerely thank M. Auburn of Inverte Inc for 
examining zooplankton sample and stomach con- 
tents of juvenile POP. We also thank the following 
people for help in collection of samples: M. Zim- 
mermann, K. McKinney, K. Smith, and the captain 
and crew of FV Ocean Explorer. We also thank 
J. Hill, D. Beauchamp, and N. Overman for the 
calorimetry work, and M. Mazur for the helpful 
discussions. This manuscript was improved with 
reviews from M. Love, K. Aydin, L. Logerwell, M. 
Wilkins, A. Moles, and three anonymous reviewers. 
This project was funded jointly by the North Pacific 
Research Board (NPRB Publication no. 198) and 
the Essential Fish Habitat Program of the Alaska 
Fisheries Science Center. This publication was also 
partially funded by the Joint Institute for the Study 
of the Atmosphere and Ocean ( JISAO) under NOAA 
Cooperative Agreement No. NA17RJ1232, Contribu- 
tion no. 1628. 
