282 
Fishery Bulletin 107(3) 
Juvenile POP diet 
Generally, the SCI was highest for small fish and lowest 
for large fish; large fish sampled in June at the north site 
had significantly fuller stomachs than large fish sampled 
in August at the north site (P<0.001; Fig. 4). The SCI 
was similar between sites for both small and medium 
fish (P=0.954 and 0.229, respectively). In August, large 
fish had significantly fuller stomachs at the south site 
than those at the north site (P=0.024; Fig. 4). 
The proportion of POP with empty stomachs varied 
among sites and months (Fig. 4). In August, the pro- 
portion of empty stomachs was higher at the north 
site for both medium and large POP (0.33 and 0.32, 
respectively). Empty stomachs were not found in small 
POP at the north site in August or in large POP at the 
north site in June (Fig. 4). 
Large copepods (>2.5 mm) comprised the majority of 
juvenile POP diets for all size classes; however, larger 
prey items such as euphausiids were consumed by me- 
dium and large juveniles (Fig. 5). Small juvenile POP 
(sampled in August) consumed almost exclusively large 
copepods, as did the large POP sampled in June. Of the 
small and medium POP sampled at the north and south 
sites in August, there were no significant differences 
by numerical or weight proportions in the three main 
prey items consumed: large copepods, euphausiids, and 
larvaceans (P>0.05). The proportion (numerical and 
weight) of euphausiids consumed by large POP juve- 
niles was significantly higher at the south site (P<0.01). 
Large POP juveniles at the north site consumed 
significantly more large copepods in June than 
in August (P<0.01). 
Zooplankton 
Zooplankton biomass, but not community com- 
position, was significantly different between 
the two sites in August (P=0.002). Average 
zooplankton biomass was three times higher 
at the north site than at the south site (Fig. 
6). Zooplankton samples at both the north and 
south sites were numerically dominated by 
large copepods. Small copepods and hyperiid 
amphipods were also numerically important 
at both sites. There were no significant differ- 
ences in the proportions of large copepods, small 
copepods, or hyperiid amphipods between sites 
(P=0.109, 0.159, 0.365, respectively; Fig. 6). 
Other zooplankton components included euphau- 
siids, chaetognaths, Limacina pteropods, and 
larvaceans. Euphausiids were more numerous 
at the north site than at the south site, but this 
difference was not significant (P= 0.792). 
Discussion 
The comparison of juvenile POP in two areas 
of the Aleutian Islands revealed spatial differ- 
ences in the condition of fish of the same size 
class. Differences in fish condition have been 
attributed to food availability in past studies; 
for example, age-0 pollock with a relatively high 
index of condition and with high growth rates 
were found in areas of high prey abundance 
(Wilson et al., 2005). In the present study, the 
quantity of prey available, as indicated by the 
settled volume of zooplankton sampled in the 
water column, was very different between the 
sites. The ring net used in this study to sample 
zooplankton, however, did not sufficiently sample 
all juvenile POP prey; therefore, conclusions 
that can be based on these data are limited. 
In August, zooplankton biomass was high and 
1 . 6 % -| 
5 1 .4% 
> 
■O 
O 1.2% - 
° 1 . 0 % - 
03 
C/3 
03 0.8% H 
CO 
(/) 
© 0 . 6 % - 
- 0.4% - 
sz 
o 
« 0.2% -| 
o 
' 0 . 0 % 
CO 
Site: 
Month: 
Fork length: 
A 
N | S 
N | S 
N 
N S 
August 
August 
June 
August 
<160 mm 
<210 mm 
>210 mm 
0.4 -| 
0.3 - 
0.2 - 
0.1 
0.0 
Site: 
Month 
B 
N S 
N S 
N 
N | S 
August 
August 
June 
August 
<160 mm 
<210 mm 
>210 mm 
Figure 4 
(A) Stomach content weight expressed as a percent of body weight 
(see SCI under heading “Juvenile POP diet” above), and (B) 
proportion of empty stomachs for three size classes of juvenile 
Pacific ocean perch (POP, Sebastes alutus) (<160 mm, <210 mm, 
and >210 mm fork length) at the north (N) and south (S) Samalga 
Island sites in August and at the N site in June, collected with a 
bottom trawl in the Aleutian Islands, Alaska. Standard error bars 
are shown for stomach fullness estimates. An asterisk indicates 
significant differences for that size class. 
