St John et al.: Diet of Plectropomus leopcirdus on the Great Barrier Reef 
189 
tions on reefs after closure (summarized in Williams and 
Russ, 1994). Also, population density of P. leopardus has 
differed in other closed-versus-open fishing zones in the 
Marine Park (Ayling et al., 1991). In contrast, the size 
structure of populations of P. leopardus on four reefs in the 
GBR showed no effect of protection from fishing after 3-4 
years of reef closure (Ferreira and Russ, 1995). Possible 
reasons for an absence of the effects of fishing include mi- 
gration by P. leopardus among reefs and small differences 
in the actual fishing pressure between open and closed 
zones. Other studies on movement of P. leopardus indicate 
that migration of 5-10 km between reefs would be highly 
unlikely (Davies, 1995; Zeller, 1997). Of a tagged popula- 
tion of 4627 P. leopardus on five reefs on the GBR, only 
1 % moved between reefs in a period of 22 months and only 
2% travelled distances of 5-7.5 km (Davies, 1995). Fishing 
pressure was not measured on any of our four reefs dur- 
ing the eight years of protection, so it is possible that fish- 
ing pressure was low on the open reefs; however it seems 
more likely that the “closed” reefs were fished illegally. 
Such violations are thought to be relatively common on 
the GBR, and illegal fishing of these prized food fishes is 
probably widespread throughout tropical waters. Another 
documented example of violations of a fishing regulation 
for a large grouper is found in the Florida Keys, where 
bans on harvesting Nassau grouper (Epinephelus striatus) 
appeared to be ineffective (Sluka and Sullivan, 1998). 
The diet of P. leopardus in our study did not differ be- 
tween fishing zones when families of prey were assessed 
by either their relative importance in the diet (dietary 
overlap) or their number of prey. Patterns between fish- 
ing zones occurred in four of the 22 families but were con- 
sidered weak because they were not detected statistically. 
Pomacentridae and Labridae, which ranked first and sec- 
ond respectively at all four reefs, were more important in 
the diet in the closed reefs, whereas Scaridae and Syn- 
odontidae were more important in the diet on open reefs. 
Information on prey availability on each reef may explain 
these results. Lastly, proportions of prey consumed from 
each of the four habitats were similar among reefs, sug- 
gesting that feeding behavior of P. leop- 
ardus did not differ among these reefs 
Two aspects of the diet of P. leopardus 
differed between the locations of the reef 
pairs. Rare prey families, which occurred 
only once in the diet in the entire study, 
were more common at the two northern 
reefs (eight families) than at the south- 
ern pair (one family). Also, P. leopardus 
from the two southern reefs consumed 
more of the large schooling Caesionidae. 
However, location of the reefs alone may 
not explain these patterns because reef 
location is confounded with time of sam- 
pling in our study. The southern pair of 
reefs was sampled one month after the 
northern pair. 
Similar to other dietary studies of 
adult P. leopardus on the GBR (Choat, 
1968; Goeden, 1978; Kingsford, 1992; 
St John 1995, 1999), our study confirmed 
that leopard coralgroupers are highly 
Table 9 
The 22 families of prey classified into four broad habitats on the reef: demer- 
sal reef (associated with substrata), benthic reef (strongly associated with reef 
substrata), midwater and adjacent sands. 
Demersal 
Benthic 
Midwater 
Adjacent sands 
Acanthuridae 
Blenniidae 
Caesionidae 
Creedidae 
Apogonidae 
Gobiidae 
Clupeidae 
Nemipteridae 
Balistidae 
Scorpaenidae 
Engraulidae 
Platycephalidae 
Labridae 
Lutjanidae 
Monacanthidae 
Pomacentridae 
Plesiopidae 
Scaridae 
Serranidae 
Siganidae 
Fistulariidae 
Synodontidae 
Table 10 
Number of prey in the diet of P. leopardus on the four reefs in each of the four habitats (demersal reef, benthic reef, midwater, and 
adjacent sands). Total number and percentage of prey as well as importance of prey in the diet (IRI, index of relative importance! 
in each habitat are included. 
Habitat 
Open 
Closed 
Total 
IRI 
% 
North 
(Nathan) 
South 
(Potter) 
North 
( Wardle) 
South 
(Noreaster) 
Number 
% 
Demersal reef 
32 
29 
22 
31 
114 
61.3 
67.0 
Benthic reef 
4 
1 
5 
0 
10 
5.4 
6.6 
Midwater 
14 
19 
9 
7 
49 
26.3 
19.7 
Adjacent sands 
5 
3 
3 
2 
13 
7.0 
6.7 
Total 
55 
52 
39 
40 
186 
100 
