182 
Fishery Bulletin 99(1 ) 
and methods” section) and baited line fish- 
ing. Fishing pressure was assessed by com- 
paring differences in the size structure of 
populations of P. leopardus between fished 
and unfished reefs using size information 
from the catch at each reef as well as fishery 
independent estimates from visual surveys 
done just prior to sampling (Ayling and Ay- 
ling 6 ; Brown et al. 7 ). 
Materials and methods 
Study sites and sampling design 
Two pairs of mid-continental shelf reefs at 
the southern end of the Cairns section of the 
GBR Marine Park were sampled in Janu- 
ary and February 1992 (Table 1). Each pair 
comprised one reef that had been closed 
to fishing for eight years (Marine National 
Park (MNP) ‘B’) and another open to com- 
mercial and recreational fishing activities 
(General Use (GU) ‘B’). These reefs will sub- 
sequently be referred to as “closed” and 
“open” zones. The northern pair, Wardle Reef 
(closed) and Nathan Reef (open), and the 
southern pair, Noreaster Reef (closed) and 
Potter Reef (open), were approximately 30 
km apart, and the reefs within pairs were 
5 and 10 km minimum distance from each 
other respectively (Fig. 1). 
Figure t 
The southern part of the Cairns section of the Great Barrier Reef Marine Park 
showing Nathan and Potter Reefs (zoned GU ‘B’, all fishing allowed) and Wardle 
and Noreaster Reefs (zoned MNP ‘B\ closed to all fishing). 
Collection of P. leopardus 
Each reef was fished by line and spear 
simultaneously. Two teams of experienced 
fishermen collected fish by spear and line 
during daylight hours (0600-1800 h). Line 
fishermen worked in pairs from two small boats and used 
single hook rigs with pilchards (Sardinops neopilchardus ) 
as bait. Spear fishermen worked in two pairs and hunted 
each fish as soon as it was seen in an attempt to obtain a 
sample representative of the size distribution of the actual 
population of coral trout. If two or more grouper were 
spotted simultaneously, the choice of the target was not 
based on size, and spear fishermen were deliberately not 
size selective. Spear fishing, however, has some inherent 
biases. Larger fish will be sighted first by spear fisher- 
6 Ayling, A. M. and A. L. Ayling. 1992. Effects of fishing pilot 
study: visual surveys on Cairns section closed reefs that will 
be opened under the new zoning plan. Unpub] . report to 
GBRMPA, PO Box 1379, Townsville, Queensland 4810, Austra- 
lia, 48 p. 
7 Brown, I. W., L. C. Squire, C. Baltus, and M. Sellum. 1996. 
Effect of zoning changes on the fish populations of unexploited 
reefs — stage 2: post-opening assessment. Unpubl. report to 
GBRMPA, PO Box 1379, Townsville, Queensland 4810, Austra- 
lia, 40 p. 
men because they will approach a diver more readily than 
smaller fish and are more conspicuous at distances (Kul- 
bicki, 1998). These biases, however, should be similar at 
all reefs. Furthermore, the detection of camouflaged spe- 
cies, such as P. leopardus, increases with disturbance of 
the habitat when divers flush out these fish earlier at dis- 
turbed or fished reefs (Kulbicki, 1998), and this distur- 
bance may increase the speared catch. Amount of catch, 
however, was not the focus of this study. 
Samples were stored on ice in the small boats and frozen 
on board the mother ship (up to several hours later). Fork 
length (FL) of captured coral trout was measured to the 
nearest 0.5 cm. 
Stomach contents 
Only stomach contents were used in dietary analysis 
of P leopardus (St John, 1995). The mouth and gills 
of each specimen were examined for regurgitated prey 
(Parrish, 1987). The stomach was opened and any con- 
tents were removed. Stomach contents were fixed in 10% 
