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cause larger fish are most likely to be captured first 
(Beverton and Holt, 1957; Hilborn, 1992). In the case 
of Batista (1988), sampling was conducted almost 30 
years ago, before the considerable increase in fishing 
effort and capture that took place in Brazil that ulti- 
mately produced a decline in populations of narrownose 
smooth-hound as predicted by Haimovici (1997). 
The explanation outlined in the previous paragraph 
is also supported by the difference observed in the 
mean length at age calculated in each study. In Hozbor 
et al. 6 , fish with ages above 5 years had lengths that 
were larger by a mean of 68.8 mm and 64.1 mm TL 
for males and females, respectively, than the lengths 
in our study. Batista (1988) presents even greater dif- 
ferences, with fish up to 80 mm TL larger than the 
fish in our study. It is likely that the largest and old- 
est specimens present in the populations sampled by 
Hozbor et al. 6 and Batista (1988) were not present in 
the population we sampled because they would have 
been removed by fishing, and their absence from our 
sample, therefore, potentially influenced the estimate 
of that we calculated. Reduction in the length by 
age is a serious consequence of overfishing in all fish 
populations (Beverton and Holt, 1957; Murawski, 2000; 
Froese, 2004); therefore, if this is the case, special at- 
tention should be paid to the possibility of stock deple- 
tion by fishing in the coastal populations of narrownose 
smooth-hound. 
Lastly, geographic location may have played a role 
in the differences in parameter estimates between Hoz- 
bor et al. 6 and Batista (1988) and our study. The sam- 
pling area for Hozbor et al. 6 extended from the Uru- 
guayan-Argentinean common fishing zone to the open 
sea region of El Rincon (39 - 41° S) in Argentina, and 
Batista (1988) performed his sampling on the Brazil- 
ian shelf near Rio Grande do Sul. Unfortunately, to our 
knowledge, biological differences between the stocks 
of narrownose smooth-hound of Argentina and Brazil 
have not been studied yet, or if they have, results re- 
main unpublished. 
Values of 0 calculated for narrownose smooth-hound 
in our study indicate a slower rate than that of other 
representatives of the Mustelus genus. Results from 
Batista (1988) and Hozbor et al. 6 indicate growth rates 
similar to those in our study, albeit slightly greater 
(Table 6). It is important to point out that despite the 
differences in the estimations of L„ and K between our 
study and those of Batista (1988) and Hozbor et al. 6 , 
the values of <j) for this species were closer for those 
studies and ours than for studies of the other Mustelus 
species examined. 
Differences in growth parameters, by sex, are com- 
monplace with sharks, especially for viviparous species 
(Cortes et al., 2010), like the night shark ( Carcharhi - 
nus signatus ; Lessa et al., 2000), the crocodile shark 
(Lessa et al., 2016), and the bigeye thresher ( Alopias 
superciliosus', Fernandez-Carvalho et al., 2015). How- 
ever, there are also examples for which no differences 
exist between sexes , as with the sandbar shark (C. 
plumbeus ; Casey et al., 1985), the oceanic whitetip 
shark (C. longimanus ; Seki et al., 1998), the sharptooth 
houndshark ( Triakis megalopterus; Booth et al., 2011), 
the bull shark (C. leucas; Neer et al., 2005), and the 
blue shark ( Prionace glauca\ Skomal and Natanson, 
2003). The differences in estimated growth parameters 
for male and female narrownose smooth-hound, that 
are observed with other species, were not statistically 
significant in our study. Despite this lack of significant 
difference, males appear to grow faster in their first 
year (G init : 137.22 mm TL of growth in the first year) 
than females (G init : 119.31 mm TL of growth in the first 
year), and males also reach a higher TL at half £ max 
(L 2 : 578.09 mm TL) than that of females (L 2 : 564.92 
mm TL), and females attain a larger L„. These types of 
differences have been reported recently for the closely 
related species, the eastern spotted gummy shark (M. 
walker i\ Rigby et al., 2016). 
Successful and sustainable management of any 
fishery is based on robust and accurate estimates of 
growth, which in turn are dependent on quality age 
and growth studies (Fernandez-Carvalho et al., 2015). 
Therefore, it is essential to improve science-based fish- 
ery data. The narrownose smooth-hound of Anegada 
Bay has a relatively fast growth in its initial year of 
life, reaching a length of approximately 400 mm TL. 
Growth slows down in subsequent years, and, accord- 
ing to our results, length at first maturity (546 and 
563 mm TL for males and females respectively; Co- 
lautti et al., 2010) is reached at an age of 7.61 years 
for females and 6.79 years for males. These values 
represent a maturation rate comparable to that of 
other species of Mustelus-, for example, the eastern 
spotted gummy shark matures at an age around 7-9 
years and at a length of 670 to 800 mm TL (Rigby et 
al., 2016). 
This late age at first maturity of the narrownose 
smooth-hound is indicative of a high susceptibility to 
fishery-induced mortality and highlights the impor- 
tance of conservation for the slow-maturing species in 
this genus. Consequently, narrownose smooth-hound 
individuals of 600 mm TL or less should be excluded 
from catches of commercial fisheries, an approach that 
would mean excluding sharks younger than, approxi- 
mately, 7 years. Despite the relatively high rate of es- 
timated natural mortality, modeling results indicate 
that protection of old adults is more appropriate than 
protection of juveniles in the case of shark fisheries 
(Prince, 2005). Whether this importance of protecting 
old adults applies to narrownose smooth-hound (or any 
other small triakid sharks) has yet to be evaluated and 
warrants further research. 
The slow growth and late age at maturity (for fish- 
ing purposes) of the narrownose smooth-hound report- 
ed here indicate that this species is vulnerable to over- 
exploitation and that the population studied may have 
signs of having been deeply affected. Ensuring both a 
sustainable population and fishery of this species re- 
quires management coordinated with a strong founda- 
tion on science-based studies for the entire distribution 
range of this species. 
