Dierking et al.: Diet composition and prey selection of Cephalophol/s argus in Hawaii 
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0 50 100 150 200 250 300 
0 50 100 150 200 250 300 
Number of stomachs analyzed 
Figure 2 
Cumulative prey curves for the assessment of sample-size sufficiency in characterizing 
dietary breadth. “Overall sample” refers to the combined Oahu and Kona Cephalopholis 
argus samples (n=285). In each panel, A-D, the number of distinct taxa identified in the 
diet is plotted against the number of stomachs analyzed. The approximation of curves 
to an asymptote indicates that sample size was sufficiently large. The order of samples 
was randomized five times, and the mean number of unique prey items and the stan- 
dard deviation for every 25 th sample were calculated from the five orders of analysis. 
The four added data points in panel A (<§)) show results of previous studies on C. argus 
(l=Hobson 1974; 2=Randall 1980; 3 = Shpigel and Fishelson 1989a; 4 = Randall and Brock 
1960). Sample size and number of identified taxa for these studies are strongly and 
significantly correlated (Pearson’s r=0.97, P=0.03). 
totic behavior (Fig. 2, left panels), which indicates that 
sample size was sufficiently large to describe dietary 
breadth. In contrast, curves for the species-level analy- 
sis based on the overall sample and for the family-level 
analysis based on the Oahu sample (Fig. 2, right pan- 
els) showed only a slight approximation to an asymp- 
tote, and dietary breadth may therefore be incompletely 
described at these levels. 
Composition of the reef fish assemblage 
Figure 3 summarizes the mean densities of the 32 differ- 
ent families of reef fishes observed on Kona reefs during 
the 2003 WHAP surveys. The families Acanthuridae 
and Pomacentridae, with densities of 69.2 and 61.8 
individuals/100 m 2 , together accounted for almost 75% 
of the total fish assemblage in terms of %N. Seven other 
families contributed at more than 1% by %N, the most 
important ones being the Labridae (9.0%) and Chaet- 
odontidae (4.6%). The importance of nocturnally active 
families may be higher than shown in Figure 3, which 
is based on daytime WHAP surveys alone. In particular, 
recalculated numerical importance for the nocturnal 
families Apogonidae, Holocentridae, and Priacanthidae 
(based on nighttime surveys showing a 90.6, 2.6, and 
1.5 times higher abundance than during daytime; see 
Material and methods section) would be 7.5%, 6.8%, and 
<0.1%, respectively. The guild of large-body piscivores 
contributed 0.7% to total fish abundance. Within this 
guild, C. argus (density=0.70 individuals/100 m 2 ) was 
the dominant taxon, contributing 56% by %N (Fig. 3) 
and 84% by %M — the larger value for the latter being 
due to a higher mean body M for C. argus compared to 
the other predators in the analysis. 
Prey selection 
All of the 10 most abundant species on Kona reefs were 
found in the stomachs of C. argus. However, although 
some fishes that were rare in the reef environment 
