Chuwen et al.: Changes in the catch rates and length and age at maturity of Cmdoglanis macrocephalus 
249 
117°20'E 117°24'E 117°28'E 
Figure 1 
Map showing the location of Wilson Inlet on the south coast of Western Australia 
and the ten sites sampled for estuary cobbler ( Cnidoglanis macrocephalus) during 
2005-08 (O) and the six also sampled in 1987-89 (*). Hatching represents the area 
closed to commercial fishing. 
offshore, deeper waters were sampled with gill nets and 
traps baited with the river prawn Macrobrachium idae. 
The seine net, which was 21.5-m long and consisted of 
two 10-m long wings (6 m of 9-mm mesh and 4 m of 
3-mm mesh) and a 1.5-m bunt of 3-mm mesh, was laid 
parallel to the shore and then hauled on to the beach. 
This net fished to a depth of 1.5 m and swept an area 
of -116 m 2 . The sunken composite multifilament gill net 
comprised six 20-m panels, each with a height of 2 m, 
but containing a different stretched mesh size, i.e., 35, 
51, 63, 76, 89, or 102 mm. The traps were 500x250x250 
mm and contained two funnel entrances 50 mm in 
diameter. Gill nets and traps were set at dusk and 
retrieved -12 hours later around dawn. Fishes were 
euthanized in an ice slurry immediately after capture. 
Seasonal values for salinity, water temperature, and 
dissolved oxygen concentration in Wilson Inlet are given 
in Chuwen et al. (2009b). 
Catch rates 
The catch rate for C. macrocephalus at each site on each 
sampling occasion during 1987-89 and 2005-08 was 
expressed as the number of fish caught overnight (-12 
h) in a gill net comprising six panels that were of the 
same length (20 m) but different mesh sizes (see above). 
Because spawning peaks in December, thus leading to 
the recruitment of the new year class in January, com- 
parisons between the catch rates in the earlier and later 
periods were restricted to using the samples collected 
seasonally between the summer and spring of 1988, 
2006, and 2007, years in which data were obtained at 
the same sites in open and closed fishing waters in each 
season (Fig. 1). Analysis of variance (ANOVA) was used 
to determine whether the catch rates with gill nets in 
Wilson Inlet were significantly related to year, season, 
and region (open vs closed waters), each of which were 
considered fixed factors. Before analysis, catch rates were 
fourth-root transformed, which was shown to be appropri- 
ate from the relationship between the log 10 of the stan- 
dard deviation and the log 10 of the mean catch rates of the 
replicate samples obtained seasonally from each region 
in each year. 4 The catch rates, derived from data col- 
lected in the winter and spring of 1987 and the summer 
and autumn of 1989, were then compared with those for 
the corresponding seasons during 2005-08 to ascertain 
whether the results obtained for these more restricted 
periods paralleled those based on seasonal data for full 
years. Mean catch rates and 95% confidence limits (CL) 
were back-transformed before being plotted or reported. 
Age determination 
The total length (TL) of each C. macrocephalus was mea- 
sured to the nearest 1 mm and its two lapillus otoliths 
were removed, cleaned, dried, and stored. One otolith 
from each fish was placed in a black dish, covered with 
methyl salicylate, and its clearly defined translucent 
zones were counted under reflected light with a dissect- 
ing microscope. Previous work by Laurenson et al. (1994) 
had validated that a single translucent zone is laid down 
annually in the lapillus otoliths of C. macrocephalus. The 
age of each fish was estimated by the number of trans- 
4 Clarke, K. R., and R. M. Warwick. 2001. Change in 
marine communities: an approach to statistical analysis 
and interpretation, 2 nd ed., 172 p. PRIMER-E, Plymouth, 
UK. 
