Chuwen et al : Changes in the catch rates and length and age at maturity of Cnidoglanis macrocephalus 
253 
Total length (mm) 
Age class (years) 
Figure 2 
Length- and age-class frequency distributions for estuary cobbler (Cnidoglanis 
macrocephalus ) caught with gill nets at the same sites in Wilson Inlet during 1987-89 
and 2005-08. Shaded areas represent the number of individuals in each length and age 
class that were caught in areas closed to commercial fishing. Four sites were sampled 
in the area open to fishing and two sites were sampled in the closed area during both 
time periods (1987-89 and 2005-2008). Sample sizes (n) for the number of individuals 
caught in open versus closed areas are given. 
to 700 mm TL, the length-frequency distribution in the 
earlier period contained a second strong modal length 
class at 560-579 mm TL, which exceeded the length 
of the vast majority of fish caught in the later period 
(Fig. 2). Consequently, the percentage of fish >430 mm 
TL, the current MLL for retention of this species, was 
far lower in 2005-08 (29%) than in 1987-89 (48%) (Fig. 
2). Although the percentage of fish greater than this 
MLL in the waters open to commercial fishing were 
similarly low in both periods (12% in 1987-89 and 10% 
in 2005-08), the percentage of such fish was less in the 
area closed to commercial fishing in 2005-08 (48%) than 
in 1987-89 (60%) (Fig. 2). 
Although the 3+ age class of C. macrocephalus was 
the best represented age class in the catches taken 
with gill nets during 1987-89, closely followed by 
the 2+ age class, the catches during 2005-08 were 
dominated by the 2+ age class and contained few age 
3+ fish (Fig. 2). The 4+ age class was also reasonably 
well represented in the earlier but not the later 
period and the percentage of fish >4+ years was 11.7% 
during 1987-89 compared with 4.5% during 2005- 
OS (Fig. 2). In both periods, the vast majority of C. 
macrocephalus >4+ years were caught in the region 
closed to commercial fishing (Fig. 2). 
Analyses of the catch rates of C. macrocephalus in 
each region of Wilson Inlet, i.e., sites open and closed 
to commercial fishing, in each season of 1988, 2006, 
and 2007, revealed that catch rates were significantly 
related to region (P<0.001), year (P<0.01), and season 
(P<0.05), and that none of the interactions between 
those main effects was significant (all P>0.05) 
(Table 1). The mean catch rate in the area closed 
to commercial fishing was 11.3 fish/12 h and far 
greater than in the area open to commercial fishing 
(1.2 fish/12 h) (Fig. 3A). Although the mean catch 
rate of C. macrocephalus in 2006 (1.9 fish/12 h) did 
not differ significantly (P>0.05) from that in 2007 
(2.5 fish/12 h), both catch rates differed significantly 
(both P<0.01) from that in 1988, i.e., 12.4 fish/12 h 
(Fig. 3B). The mean catch rates of C. macrocephalus 
in Wilson Inlet declined from their maxima in summer 
and autumn (8.6 and 6.8 fish/12 h, respectively) to 
their minima in winter (1.3 fish/12 h) and rose again 
in spring (3.4 fish/12 h) (Fig. 3C). On the basis of 
the ANOVAs, and recognizing that there was no 
interaction with either region or season, we determined 
that the mean catch rates in the winter and spring 
of 1987 were greater and differed significantly from 
those in the corresponding seasons of 2005-08 (each 
PcO.001). Mean catch rates were also greater, but 
not significantly different (P>0.05), in four of the six 
comparisons between the summer and autumn of 1989 
and the corresponding seasons of 2005-08. 
