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Fishery Bulletin 107(4) 
macrozooplankton. This finding generally concurred 
with that from other studies of the diets of rockfish 
species during normal ocean conditions (Pereyra et 
ah, 1969; Lorz et al., 1983; Brodeur and Pearcy, 1984). 
However, the dominant prey species differed from previ- 
ous studies. 
The results from the PCA on the diet composition of 
the rockfish species indicate that patterns in their diets 
are associated with geographical components (latitude, 
depth), temporal components (annual, seasonal, diel), 
and their interactions. The complicated interactions 
between the geographical and temporal variables in the 
model for S. flavidus from the NMFS summer survey 
collections, in particular, indicate that the predation 
pattern for this species was very temporally localized 
and thus that S. flavidus is an opportunistic feeder. 
An opportunistic feeder in fish ecology refers to a fish 
species that takes advantage of transitory food sources 
that are normally outside of its usual diet. The term 
also describes disproportionately high feeding on food 
sources that are unusually abundant in a given time 
frame (Gerking, 1994). 
The study by Reilly et al. (1992) on the diets of the 
pelagic stages of five juvenile rockfish species ( S . fla- 
vidus, S. entomelas, S. goodei, S. jordani, and S. pau- 
cispinis) off central California found strong annual 
variation, as well as spatial variation (latitude, depth, 
A 
B 
Figure 6 
Predicted values by fish species for each seasonal quar- 
ter from the general linear model (GLM) fitted to (A) the 
principle component analysis (PCA) axis 1 scores and (B) 
the PCA axis 2 scores from the diet composition data of 
the quarterly collections. 
and interaction) in the diets, but no significant varia- 
tion with fish size-class. Even though the life stage 
of the samples was different from that in our study 
(adults), there was a strong similarity in terms of sig- 
nificant extrinsic factors related to dietary variability. 
The opportunistic feeding pattern during the juvenile 
stage was also consistent with our finding for adult 
stage of S. flavidus and S. entomelas. From the find- 
ing of high interannual variability in the diet with low 
intraspecific dietary overlap, they deduced that some 
pelagic juvenile Sebastes spp. had an opportunistic 
feeding strategy. 
One noteworthy finding in our study was that the ear- 
ly juvenile stage of M. productus often occurred in the 
stomachs of S. flavidus and S. entomelas in the spring 
and summer of 1998, but then disappeared from both 
species diets later in the year. Previous studies have 
not reported Pacific whiting as prey of S. flavidus in the 
northeast Pacific. Pacific whiting are generally known 
to spawn off southern California during winter (Bailey 
et al., 1982). However, Phillips et al. (2007) provided 
evidence that since 2003 there have been northward 
shifts in the nursery areas of Pacific whiting juveniles 
into southern Oregon. The appearance of whiting in 
the diets of S. flavidus in our study may be due to the 
anomalous effects of the 1997-98 El Nino or may reflect 
a more persistent change. 
Another unusual southern species in the diets was 
the euphausiid species, N. simplex. This prey species 
was commonly observed in the stomach samples of 
all three rockfish species during the spring of 1998. 
Brodeur (1986) found this southern species in the 
stomachs of some fish species off the Pacific North- 
west during the 1983 El Nino. Brodeur and Pearcy’s 
(1984), during the non-El Nino year of 1980, did not 
report N. simplex in the diet of either S. flavidus or 
S. pinniger. Studies of zooplankton off Oregon and 
Vancouver Island, farther north of the sampling loca- 
tions in our study, confirmed the appearance of some 
southern zooplankton species, including N. simplex, 
during the 1997-98 El Nino years (Mackas and Gal- 
braith 2002; Peterson et al., 2002; Tanasichuk and 
Cooper 2002; Keister et al., 2005). 
Another noteworthy finding of our study was that 
jellyfish species were the dominant prey for S. flavi- 
dus and S. entomelas in some quarters. The amount 
and the occurrence of jellyfish species in the diets 
of S. flavidus from the 1998 summer survey collec- 
tion were much higher than reported by Brodeur 
and Pearcy (1984). The importance of euphausiids 
as prey for many planktivorous fish populations, 
including rockfish species in the northeast Pacific 
Ocean, has been established in previous studies. 
However, jellyfish species (gelatinous zooplankton) 
were ordinarily regarded as minor food sources 
for most rockfish species. Raskoff (2001) reported 
detecting changes in the species composition and 
abundance of jellyfish species off Monterey Bay in 
California during the El Nino events of 1991-92 
and 1997-98. Considering the rapid growth rate 
