464 
Diet composition and prey selection 
of the introduced grouper species peacock hind 
{Cephalopholis argus ) in Hawaii 
E-mail address for contact author: jan.dierking@univmed.fr 
1 Department of Zoology 
University of Hawaii 
2538 The Mall 
Honolulu, Hawaii 96822 
2 Present address: Centre d'Oceanologie de Marseille, UMR CNRS 6540 
Universite de la Mediterranee, Station Marine d'Endoume 
Rue de la Batterie des Lions 
13007 Marseille, France 
3 Hawaii Division of Aquatic Resources, Honokohau Marina 
74-380B Kealakehe Pkwy 
Kailua-Kona, Hawaii 96740 
Abstract — The introduced grouper 
species peacock hind ( Cephalopholis 
argus), was the dominant large-body 
piscivore on the Main Hawaiian Island 
(MHI) reefs assessed by underwater 
visual surveys in this study. However, 
published data on C. argus feeding 
ecology are scarce, and the role of this 
species in Hawaiian reef ecosystems 
is presently not well understood. Here 
we provide the first comprehensive 
assessment of the diet composition, 
prey electivity (dietary importance 
of prey taxa compared to their avail- 
ability on reefs), and size selectiv- 
ity (prey sizes in the diet compared 
to sizes on reefs) of this important 
predator in the MHI. Diet consisted 
97.7% of fishes and was characterized 
by a wide taxonomic breadth. Surpris- 
ingly, feeding was not opportunistic, 
as indicated by a strongly divergent 
electivity for different prey fishes. In 
addition, whereas some families of 
large-body species were represented 
in the diet exclusively by recruit-size 
individuals (e.g., Aulostomidae), sev- 
eral families of smaller-body species 
were also represented by juveniles 
or adults (e.g., Chaetodontidae). 
Both the strength and mechanisms 
of the effects of C. argus predation 
are therefore likely to differ among 
prey families. This study provides the 
basis for a quantitative estimate of 
prey consumption by C. argus, which 
would further increase understanding 
of impacts of this species on native 
fishes in Hawaii. 
Manuscript submitted 18 December 2008. 
Manuscript accepted 24 June 2009. 
Fish. Bull. 107:464-476(2009). 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Jan Dierking (contact author ) 1 2 
Ivor D. Williams 3 ' 4 
William J. Walsh 3 
4 Hawaii Cooperative Fishery Research Unit 
Department of Zoology 
University of Hawaii at Manoa 
Honolulu, Hawaii 96822 
The grouper species peacock hind 
( Cephalopholis argus) (Serranidae: 
Epinephelinae), a reef fish predator 
that is native over most of the Indo- 
Pacific region, was introduced to the 
Main Hawaiian Islands (MHI) in 1956 
as part of an introduction program of 
snapper and grouper species intended 
to enhance nearshore fisheries (Ran- 
dall, 1987). Today, this non-native 
predator occupies a dominant posi- 
tion in the guild of large piscivores 
on many reefs in the MHI (see Results 
section). As impacts of piscivores on 
prey fishes have been demonstrated 
in a number of studies (e.g., Webster, 
2002; Hixon and Jones, 2005), the 
abundance of C. argus raises the ques- 
tion of how, if at all, it affects native 
reef fishes in Hawaii. However, the 
only published study of C. argus feed- 
ing in the MHI to date was based on 
a sample of 10 specimens (Hobson, 
1974), which is insufficient to eluci- 
date feeding patterns. 
Groupers are among the most com- 
mon predatory reef fishes worldwide 
(Parrish, 1987). They play an impor- 
tant role in shaping reef communities 
(Goeden, 1982; Parrish, 1987) and 
are of large commercial importance 
in coral reef fisheries (Heemstra and 
Randall, 1993). However, data on the 
general feeding ecology of this family 
remain surprisingly scarce (Beukers- 
Stewart and Jones, 2004). In addition, 
although concern about declines of 
many grouper species worldwide due 
to overfishing has led to a renewed 
research focus on this family (Mor- 
ris et al., 2000), much of the work to 
date has concentrated on a limited 
number of species, e.g., the coral trout 
( Plectropomus leopardus) in Austra- 
lia (e.g., Kingsford, 1992; St. John, 
1999), the Nassau grouper ( Epineph - 
elus striatus) in the Caribbean Sea 
(e.g., Eggleston et al., 1998), or the 
dusky grouper (Epinephelus margin- 
atus ) in the Mediterranean Sea (e.g., 
Renones et al., 2002). 
Most studies of grouper diet have 
been based on analysis of stomach 
contents. However, because of the 
difficulty of obtaining large grouper 
samples (Beukers-Stewart and Jones, 
2004), as well as the high prevalence 
of empty stomachs due to prey regur- 
gitation during capture and because 
of the characteristics of grouper feed- 
