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to heavy exploitation of C. macrocephalus during the 
last two decades is supported by the observation that, 
although fishery-independent catch rates have fallen, 
the commercial catches of this species in Wilson Inlet 
have shown no clear tendency to decline between these 
two periods. 1 This finding emphasizes the difficulties 
in obtaining reliable values for the catch per unit of 
effort of a species by using fishery-dependent data for 
the multispecies fishery of which that species is just 
one contributor. 
A comparison of the age-frequency data for open and 
closed areas indicated that the relatively small area 
that is closed to commercial fishing in Wilson Inlet 
provides some protection for the stock of C. macro- 
cephalus in that estuary. Thus, although the catches 
in open waters contained appreciable numbers of age 
1+ and 2+ C. macrocephalus, they yielded few age 3 + 
fish, whereas those in closed waters contained large 
numbers of 3+ individuals, the age at which this spe- 
cies attains, on average, the MLL of 430 mm TL for 
retention in the fishery. Furthermore, the catch rates, 
and thus relative abundances, were greater in closed 
than open waters. 
The MLL for C. macrocephalus during 1987-89 was 
318 mm TL, and thus considerably less than the L g0 
of 449 mm TL for females at maturity in that period. 
Therefore, at that time, both mature and immature 
individuals would have been heavily harvested, leading 
to selection pressures for a reduction in the length at 
maturity (Law and Grey, 1989; Heino, 1998; Ernande 
et al., 2004). Although the MLL was increased to 430 
mm TL in 1994, it is reasonable to suggest that sub- 
stantial numbers of both immature and mature indi- 
viduals continued to be fished, which would account for 
selection having led to a reduction in the L 50 of females 
at maturity to 419 mm TL during 2005-08. 
Comparisons between the reproductive data for 
C. macrocephalus in Wilson Inlet during the two sam- 
pling periods indicated that the females of this species 
matured at a smaller size and younger age during 
2005-08 than during 1987-89, with respective L 50 s of 
419 and 449 mm TL and A 50 s of 2.9 and 3.5 years. The 
corresponding downward shift of the reaction norms for 
maturation and the attainment of sexual maturity at 
smaller sizes and younger ages by the heavily fished 
C. macrocephalus parallel the trends exhibited by the 
reproductive parameters for populations of several fish 
species that were also heavily exploited by commercial 
fishing (e.g., Trippel, 1995; Olsen et al., 2004; Morita 
and Fukuwaka, 2007; Neuheimer and Taggart, 2010). 
They also parallel the patterns exhibited by natural 
populations of guppies ( Poecilia reticulate) that were 
subjected to either high or low predation, which thus 
served as surrogates for the presence or absence of 
commercial fishing (Reznick and Ghalambor, 2005). 
A reduction in the size and age at maturity of heav- 
ily fished stocks may reflect an increased selection for 
rapidly maturing individuals because these would be 
more likely to reproduce before being captured (Mar- 
shall and Browman, 2007). Indeed, Olsen et al. (2005) 
provided evidence that the trend for earlier maturation 
in stocks of the heavily exploited Atlantic cod ( Gadus 
morhua) halted and even showed signs of reversing 
after the fisheries for those stocks had been closed. 
The shift of the maturation reaction norms toward 
lower lengths indicates that there has been a genetic 
response of the stock of C. macrocephalus to the inten- 
sive exploitation to which it has been shown to have 
been subjected. 
Although the total mortality of C. macrocephalus in 
Wilson Inlet essentially doubled between 1988-89 and 
2006-08, the differences between the predicted lengths 
at age of fish at each of the dominant integer ages in 
the two periods were <2% and thus considered not to 
be of biological significance. This absence of a shift in 
growth after heavy fishing pressure is consistent with 
the conclusions from a meta-analysis of 73 commercially 
fished marine stocks that there was no evidence in gen- 
eral, that growth rate was related to fishing intensity 
(Hilborn and Minte-Vera, 2008). The lack of a clear 
change in growth after heavy exploitation contrasts 
with the situation recorded for a number of species in 
which growth was found to change with heavy exploita- 
tion (e.g., Cassoff et al., 2007; Melvin and Stephenson, 
2007; Swain et al., 2007). Such changes have generally 
been attributed either to fishery-induced evolution or 
density-dependent effects. 
Evolutionary effects would account for the reduc- 
tion in growth that has been recorded for a number of 
heavily exploited fish populations through size-selec- 
tive harvest of individuals with the genotype for fast 
growth (e.g., Jprgensen et al., 2007; Swain et al., 2007; 
Brown et al., 2008). The density-dependent alternative 
cause would account for the increased growth that 
occurs in some fish populations following heavy ex- 
ploitation and which is considered to represent a com- 
pensatory response to the decline in density brought 
about by the removal of a large number of individu- 
als and thus a reduction in competition for resources 
(e.g., Trippel, 1995; Cassoff et al., 2007). Because the 
marked decline in fish density of C. macrocephalus 
in Wilson Inlet between 1987—89 and 2005—08 was 
not accompanied by an increase in growth, this spe- 
cies did not undergo a density-dependent phenotypic 
response between the two periods. This finding, in 
conjunction with the change in the maturation reac- 
tion norms, supports our conclusion that the changes 
in the length and age at maturity of C. macrocephalus 
over time probably represent a genotypic response to 
fishing pressure. 
Conclusions 
This study provides further strong indications that 
heavy fishing pressure can lead to changes in the bio- 
logical characteristics of fish stocks, such as matura- 
tion, and thus these biological characteristics should 
be considered as variables rather than constants, as 
has often been assumed to be the case by managers. 
