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Fishery Bulletin 107(3) 
and the other half in the freeze dryer. Also, twenty 
two randomly selected fish were homogenized and 
divided in half; one half was freeze-dried, the other 
half was oven-dried, and the energy content of 
both halves was determined with the carorimeter 
to determine if there were differences in energetic 
content attributable to the two drying methods. 
Juvenile POP diet 
Whole blotted wet weights of stomach contents 
were recorded. Prey items were identified to a 
general taxonomic level (large (>2.5 mm) cope- 
pods, small (<2.5mm) copepods, euphausiids, 
larvaceans, Limacina spp., chaetognaths, hype- 
riid amphipods, other), which were counted and 
weighed. Numerical and weight proportions of 
each prey group in an individual stomach were 
calculated and then averaged over all fish within 
each size category sampled at a site. The number 
of empty stomachs was recorded; however, empty 
stomachs were not included in average diet com- 
position calculations. When the average percent 
number of a prey item was less than 5%, it was 
grouped in the “other” category. A stomach con- 
tent index (SCI) was estimated as the stomach 
content weight as a proportion of the fish weight 
and averaged over all fish in each size category 
at each site. 
Zooplankton 
In August, two zooplankton samples were collected at 
each of the north and south sites with a 1-m ring net 
(505 -p mesh) hauled vertically from depths of 40-105 m. 
The volume filtered (m 3 ) was estimated as the product 
of the area of the ring net opening and the maximum 
depth from which it was hauled (recorded by a tem- 
perature-depth recorder attached to the net bridle). 
The relative biomass of zooplankton in each study area 
was estimated as the settled volume of zooplankton per 
volume of water filtered. Zooplankton samples were pre- 
served in 5% buffered formalin for laboratory analysis. 
Taxonomic components of the zooplankton samples were 
examined in the same manner that prey were enumer- 
ated from juvenile POP stomach contents. 
Statistical analyses 
An analysis of variance (ANOVA) was used to test for 
differences in log-transformed juvenile POP CPUE in 
August between sites, with site, size class, and the 
interaction term as factors. An ANOVA was used to test 
for differences in the juvenile POP response variables: 
wet-weight residuals, dry-weight residuals, energy 
content, and percent number and weight of main prey 
items. Site was the factor tested for all size classes of 
fish sampled in August. In June, only the north site 
was sampled for juvenile POP; therefore comparisons 
with the south site were not possible for the month 
70 
60 - 
50 - 
40 - 
30 - 
r-Tl 
H 
■ N, June 
□ N, August 
□ S, August 
Fork length (mm) 
Figure 2 
Length frequency of juvenile Pacific ocean perch (POP, Sebastes 
alutus) collected with a bottom trawl at sites north (N) and 
south (S) of Samalga Island in August and at the N site in 
June. Juvenile POP were divided into three size classes based 
on this length frequency (<160 mm, <210 mm, and >210 mm 
fork length), which correspond to ages 1-2, 3, and 4-5 years, 
respectively. 
of June. For large fish at the north site the factors 
tested were month, site, and a month-site interaction 
term. The nonparametric Wilcoxon rank-sum test was 
used to determine if the SCI was significantly differ- 
ent between sites for each size class of juvenile POP. 
ANOVAs were used to test for significant differences 
in the numerical proportions of major taxa found in the 
zooplankton samples between sites in August. 
Results 
Juvenile POP abundance and size classes 
Juvenile POP were caught in the two trawl hauls con- 
ducted at each of the two sites in August and the two 
trawl hauls conducted at the north site in June. Overall 
catch per unit of effort (log [CPUE+ 1]) estimates indi- 
cated that the abundance of juvenile POP was signifi- 
cantly higher (P- 0.027) at the south site (mean=4.22, 
SE = 0.53) than at the north site in August (mean=1.82, 
SE = 0.63). There were no significant differences in CPUE 
among size classes, and the interaction between size 
class and site was also insignificant. The average CPUE 
at the north site in June (mean=2.22, SE=1.71) was 
slightly higher than that measured in August at the 
same site. 
Juvenile POP fork lengths ranged from 83 to 249 mm. 
Three size classes of juvenile POP were apparent in a 
length-frequency plot (Fig. 2): small (<160 mm FL), me- 
dium (160-210 mm FL), and large (>210 mm FL). These 
size categories roughly correspond to five age classes of 
