St John et al.: Diet of Plectropomus leopardus on the Great Barrier Reef 
187 
Table 6 
The index of relative importance (IRI) calculated for each fish family of prey and expressed as a percentage of the total for all identi 
fled fish families in the diet of P. leopardus, grouped by reef, fishing zone, and total. Small-size schooling fishes are underlined. 
Reefs open to fishing Reefs closed to fishing 
North South North South 
Prey families 
(Nathan) 
(Potter) 
Both 
(Wardle) 
(Noreaster) 
Both 
Total 
Pomacentridae 
23.4 
16.9 
20.8 
32.2 
38.9 
35.4 
27.8 
Labridae 
16.6 
13.3 
15.4 
26.4 
25.9 
26.0 
20.6 
Scaridae 
15.8 
14.3 
15.0 
9.0 
4.9 
9.8 
Clupeidae 
10.6 
9/7 
10.1 
03 
71 
7/7 
09 
Caesionidae 
20.7 
8.5 
1.4 
13.4 
8.1 
8.9 
Synodontidae 
4.9 
8.5 
6.1 
1.9 
3.5 
2.7 
4.7 
Blenniidae 
0.9 
1.4 
1.1 
15.1 
7.0 
4.4 
Acanthuridae 
3.9 
5.8 
4.7 
3.0 
1.4 
3.2 
Serranidae 
4.7 
2.0 
3.5 
2.0 
1.1 
2.2 
Scorpaenidae 
7.1 
4.4 
1.8 
Apogonidae 
1.0 
5.4 
3.0 
1.6 
Nemipteridae 
5.3 
3.3 
1.3 
Fisfulariidae 
1.0 
1.1 
1.1 
1.6 
0.8 
0.9 
Engraulidae 
L9 
TO 
T8 
08 
09 
Plesiopidae 
2.7 
1.2 
0.7 
Gobiidae 
1.9 
1.0 
0.5 
Balistidae 
1.5 
0.7 
0.4 
Creedidae 
1.4 
0.7 
0.3 
Platycephalidae 
1.3 
0.7 
0.3 
Siganidae 
1.3 
0.6 
0.3 
Lutjanidae 
1.0 
0.5 
0.2 
Monacanthidae 
0.9 
0.5 
0.2 
No. of P. leopardus with prey 
92 
102 
194 
100 
86 
186 
380 
significantly between fishing zones (at P=0.01 level of sig- 
nificance, Table 8, see “Materials and methods” section for 
explanation). Furthermore, when pooled by location, the 
numerical composition of the diet of P. leopardus on south- 
ern and northern reefs differed significantly (Table 8). 
When categorized by their characteristic habitat (Table 
9), the number of prey did not differ significantly among 
reefs (Fisher’s exact test| 9 |=14.7, P=0.10) nor between fish- 
ing zones (Fisher’s exact test[ 3 j=3.3, P= 0.35, Table 10). 
Fishes in the majority of prey families (n=ll) lived in the 
demersal reef habitat (Table 9), which was the most im- 
portant source of prey for P leopardus (61% by number, 
IRI=67%, Table 10). Prey in three or four families lived 
in each of the benthic reef, midwater, and adjacent sandy 
habitats (Table 9). The large number of midwater prey at 
Potter Reef (Table 10) reflected the relatively large num- 
ber of Caesionidae consumed at this reef (Table 4). 
Discussion 
Overall, the diets of P leopardus from reefs in the two 
fishing zones were not dissimilar. Dietary overlap was 
high between P. leopardus from the reefs with open zones 
and reefs with closed zones for eight years. When com- 
pared to natural variation in diet among P. leopardus on 
the GBR, these values of overlap were very high because 
there was less similarity in the diet among regional popu- 
lations of P leopardus (Schoener a value of dietary over- 
lap ranged from 0.26 to 0.42, St John, 1995) and at one 
reef sampled over time (Schoener a value of dietary over- 
lap ranged from 0.44 to 0.84, St John, 1995). Generally, 
feeding behavior of P leopardus was similar between fish- 
ing zones. 
The lack of dietary differences between P leopardus on 
open and closed reefs is consistent with the lack of mean- 
ingful trends in comparing the size and age structures of 
these populations. Using the catch of both fishing meth- 
ods, Brown et al. 7 found a slightly higher abundance of 
legal-size (>38 cm TL) leopard coralgrouper on the closed 
reefs, as well as a greater proportion of older fish (4+ year 
class). But, fishing affected the size and age structure of 
populations on the two open reefs very differently; Na- 
than Reef showed a large recruitment of the one year class 
(Brown et al. 7 ) and differed from all other reefs. In visual 
surveys ofP leopardus at the four reefs, Brown et al. 7 de- 
tected a greater density of larger P leopardus on closed 
reefs. In contrast, Ayling and Ayling 6 found no differences 
between fishing zones in the density, average length, and 
recruitment of P leopardus when surveying the same reefs 
