470 
Fishery Bulletin 107(4) 
Table 3 
Composition of the fish portion of the diet of peacock hind ( Cephalopholis argus) from Hawaii Island (n = 179) and Oahu (rc = 106), 
based on fish prey identified to at least the family level. Crustaceans were excluded from the analysis because of their relatively 
minor dietary importance for C. argus from both islands ( %IRI =1.9% and 3.3%, respectively). Dietary importance is indicated 
by percent by number (%IV), percent by occurrence (%0) (calculated on the basis of full stomachs), percent by mass (%M), and 
percent index of relative importance ( %IRI ). 
Family 
Island 
Hawaii 
Oahu 
%N 
%0 
%M 
%IRI 
%N 
%o 
%M 
%IRI 
Acanthuridae 
16.9 
9.4 
13.0 
20.9 
8.6 
5.7 
11.9 
7.1 
Apogonidae 
3.1 
1.9 
1.2 
0.6 
2.9 
1.9 
1.7 
0.5 
Aulostomidae 
6.2 
3.8 
3.1 
2.6 
5.7 
3.8 
2.0 
1.8 
Balistidae 
4.6 
2.8 
9.1 
2.9 
— 
— 
— 
— 
Chaetodontidae 
7.7 
4.7 
10.1 
6.2 
2.9 
1.9 
2.1 
0.6 
Cirrhitidae 
3.1 
1.9 
0.9 
0.6 
5.7 
3.8 
7.9 
3.2 
Holocentridae 
24.6 
15.1 
7.5 
35.8 
— 
— 
— 
— 
Kuhliidae 
1.5 
0.9 
2.5 
0.3 
— 
— 
— 
— 
Labridae 
1.5 
0.9 
0.2 
0.1 
2.9 
1.9 
7.0 
1.1 
Monacanthidae 
6.2 
2.8 
1.6 
1.6 
31.4 
18.9 
10.3 
48.6 
Mullidae 
4.6 
2.8 
5.8 
2.2 
— 
— 
— 
— 
Pomacanthidae 
— 
— 
— 
— 
2.9 
1.9 
5.0 
0.9 
Pomacentridae 
1.5 
0.9 
0.9 
0.2 
5.7 
3.8 
7.3 
3.0 
Priacanthidae 
9.2 
5.7 
9.2 
7.7 
11.4 
3.8 
15.2 
6.2 
Scaridae 
9.2 
5.7 
34.8 
18.4 
17.1 
11.3 
19.1 
25.3 
Synodontidae 
— 
— 
— 
— 
2.9 
1.9 
10.5 
1.6 
(“the wild”) in Kona were important components of C. 
argus diet (e.g., Priacanthidae: %N reef environment <0.1%, 
%N diet =9.2%), others such as the Pomacentridae, although 
highly abundant on Kona reefs (%A=31.5%), had low 
dietary importance (%iV=1.5%) (Fig. 3, Table 2). Con- 
sequently, the electivity values of prey families ranged 
widely, from values of E t near 1 (strong preference) to 
-0.91 (strong avoidance). This pattern was consistent 
both for diurnally and nocturnally active taxa (Fig. 4). 
Specifically, of the nocturnal taxa, priacanthids and 
holocentrids were highly preferred, whereas apogonids 
were avoided. Diurnally active families can be divided 
into three broad categories based on their electivity 
(Fig. 4) and their abundance on reefs (Fig. 3): 1) nega- 
tive electivity, large wild abundance (Pomacentridae, 
Labridae, Acanthuridae); 2) moderate positive electivity, 
moderate to large wild abundance (e.g., Chaetodontidae, 
Mullidae, Scaridae); and 3) large positive electivity, low 
wild abundance (Aulostomidae, Monacanthidae). 
Prey-size selection 
The mean TL of reef fishes in the diet of C. argus was 
7.2 cm, and was thus significantly smaller than the 
mean TL of reef fishes in the wild of 9.1 cm (Kolmogo- 
rov-Smirnov test, Z) = 0.11, P=0.034) (Fig. 5). Mean size 
in the diet was consistently lower than mean size in the 
wild for all analyzed prey families. However, specific 
patterns differed strongly. On one end of the spectrum, 
for generally small-body families, such as the Acanthuri- 
dae and Chaetodontidae, differences between consumed 
and wild sizes were near significant (OAcanthuridae = ^-^^> 
P=0.057) or significant (£ C haetodontidae=°- 55 > F=0.026), 
but small in absolute terms, with size classes occurring 
in the diet overlapping strongly with those observed in 
the wild. The Scaridae (D = 0.42, P=0.021) represented 
an intermediate case, with predation focused on the 
smaller size classes present in the wild, but clear overlap 
between size-frequency distributions in the diet and in 
the wild. Finally, for the generally large-body families 
Monacanthidae (D = 0.47), Aulostomidae (Z> = 0.82), and 
Holocentridae (D = 0.99), size differences between the diet 
and the wild were large and highly significant (P<0.01), 
and sizes as small as in the diet were rarely observed 
in the wild (Fig. 5). 
Discussion 
The comparison of reef fish densities in this study showed 
that C. argus constituted more than half of the guild of 
large piscivores in Kona by numerical abundance, and 
more than 80% of this guild by biomass. Because con- 
sumption partly depends on the biomass of a predator 
(Cortes, 1996), it therefore appears safe to say that C. 
argus has become the dominant large-body predatory 
