Dierking et al.: Diet composition and prey selection of Cephalopholis argus in Hawaii 
465 
ing ecology (Dierking and Meyer, in 160° W 
press), detailed descriptions of grou- 
per diet remain rare. Notably, only 
one study of C. argus diet (Randall 
and Brock, 1960), and a few studies of 
other grouper species (but see Kings- 
ford, 1992; St. John, 1999; Beukers- 
Stewart and Jones, 2004), have been 
based on more than 50 full stomachs. 
Interpretation of feeding patterns is 
further complicated by the lack of stud- 
ies comparing dietary composition with 
prey availability in the wild (but see 
Beukers-Stewart and Jones, 2004). 
We examined the feeding patterns 
of C. argus based on stomach content 
analysis of the largest sample of this 
species (n = 285) available to date. In 
addition, we assessed the patterns in 
the context of the composition of the 
reef fish assemblage in Hawaii, which 
was determined by underwater visual 
surveys. The main goal was to describe 
the diet composition, prey electivity (di- 
etary importance of a taxon compared 
to its availability on reefs), and size 
selectivity (prey sizes in the diet com- 
pared to sizes on reefs) of C. argus in Hawaii. Second- 
ary goals were to assess the mechanisms by which 
this non-native predator may affect prey fishes and to 
provide data required for the quantitative estimation of 
prey consumption by this species. 
Material and methods 
Study organism and sampling sites 
To our knowledge, the establishment of C. argus in 
Hawaii represents the first documented case of the suc- 
cessful invasion of a non-native habitat by a grouper. 
Today this generally piscivorous species (Parrish, 1987) 
is found around all of the MHI. It is particularly abun- 
dant along the western coastline of the island of Hawaii 
(Kona coast hereafter, following common terminology 
in Hawaii), which harbors some of the least disturbed 
reefs in the MHI and is the source of important economic 
revenues from diving tourism and the aquarium fish 
industry (Tissot et al., 2004). Despite its abundance, a 
fishery for C. argus never developed because it turned 
out to be a carrier of ciguatoxin, the agent of ciguatera 
fish poisoning (Dierking and Campora, 2009). 
Cephalopholis argus specimens from the Kona coast 
(71=179, 11 sites) and from the island of Oahu (n=106, 6 
sites) (Fig. 1) were obtained by spearfishing with scuba 
in July 2003. Divers attempted to spear all sighted 
individuals regardless of size or behavior pattern (e.g., 
active swimming, resting). Collections took place be- 
tween 0924 and 1522 hours at a mean depth of 11.6 m. 
Speared specimens were immediately (i.e., underwater) 
156° W 
-21° N 
19° N 
Figure t 
Map of the Main Hawaiian Islands, with peacock hind ( Cephalopholis 
argus) collection sites marked by open circles, and underwater visual 
survey sites along the Kona coast marked by asterisks (Note: asterisks 
were moved offshore from actual survey locations to avoid overlap with 
sample site symbols). 
Table 1 
Morphometic relationships between total length 
standard length (SL, in cm), and wet mass (M, 
for peacock hind ( Cephalopholis argus) in Hawaii 
regression fit. 
(TL), 
in g) 
r 2 = 
Relationship 
a b 
n 
r 2 
M = a TL b 
0.0125 3.122 
no 
0.98 
M = a SL b 
0.0309 3.013 
no 
0.97 
SL = a + b TL 
-0.244 0.8494 
304 
0.99 
sealed in plastic bags to avoid stomach content loss 
from regurgitation commonly observed in groupers (Di- 
erking and Meyer, in press). In the laboratory, standard 
length (SL) and total length (TL) (equal to fork length 
in C. argus due to their rounded caudal fin shape) were 
recorded to the nearest mm. Wet mass (M) of C. argus 
from the Oahu sites was measured to the nearest 5 g. 
Based on these measures, morphometric relationships 
(SL-M, TL-M, SL-TL) (Table 1) were calculated. The 
SL-M equation was then used to estimate the wet mass 
of Kona specimens, which could not be measured in the 
field owing to scale malfunctioning. 
Diet composition 
To determine the diet composition of C. argus, stomachs 
of all specimens were opened and any prey items were 
removed. The analysis of contents then followed the 
procedures described by Hyslop (1980). Specifically, for 
