204 
Fishery Bulletin 115(2) 
by Kalish (1991), values from otoliths (-1.141%o 
[SE 0.20]) corresponded with water temperature values 
of 21-24°C, matching the observed sea-surface temper¬ 
ature of the waters off Rio de Janeiro. Similarly, 
values of the otoliths (0.381%© [SE O.lOj) from southern 
samples corresponded with water temperature values 
of 18-21°C, matching the sea-surface temperature at 
the hatching location of tainha as reported by Lemos 
et al. (2014). 
Lemos et al. (2014) suggested that the peak spawn¬ 
ing of the southern population of tainha occurs in 
June off the coast of the states of Santa Catarina 
and Parana. According to our results, this reproduc¬ 
tive event provides the annual supply of juveniles of 
tainha for the entire southern stock. Young-of-the-year 
disperse southward and are distributed among differ¬ 
ent nursery areas along the southern coast of Brazil. 
Vieira (1991) has described the process of dispersion of 
juvenile tainha along the coast. 
The correlation of 8^^C between 8i®0 in biological 
carbonates may indicate kinetic and metabolic ef¬ 
fects (McConnaughey, 1989). In otoliths, the correla¬ 
tion between 8^®0 and 8^^C is not entirely dominated 
by kinetic effects, such as it is in corals (Devereux, 
1967; Kalish, 1991; Gao and Beamish, 2003). This 
correlation is induced by biological fractionation and 
may exhibit different relationships (Gao et al., 2005; 
Deutsche and Berth, 2006). In contrast to 8^®0, 8^^C 
from otoliths are not in equilibrium with 8^^C values 
of sea water (Kalish, 1991). About 30% of aragonite 
carbon is derived from metabolism and is directly 
related to changes in diet (Kalish, 1991; Gao et al., 
2001). The remaining 70% of aragonite carbon comes 
from DIG (Kalish, 1991). The isotope ratio of otolith 
carbonate is a mixture of these 2 fractions; therefore, 
the interpretation of 8^^C is not as straight forward as 
it is for 8^®0 (Kalish, 1991). 
As with most species of mullets, for tainha, the in¬ 
gestion of diatoms and the presence of inorganic sedi¬ 
ment in the stomach starts at about 30 mm TL, when 
juveniles begin to feed near the bottom at the surf zone 
(Vieira, 1991). There were no significant differences 
(ANOVA: P>0.05) in sizes and weights of individuals 
among sites (Table 1) that could represent differences 
in metabolic rates (Campana, 1999). Most of the 8^^C 
incorporated into the otolith is derived from DIG (Ka¬ 
lish, 1991). The 8 ^^Gdic may be subjected to small iso¬ 
topic variations at different latitudes and in different 
water masses (Kroopnick, 1980; Thorrold et al., 1997). 
For instance, b^^Goic values in the open ocean are fair¬ 
ly uniform, around 1%©; however, in environments with 
variable freshwater input, may vary from -5 
to -10%c (Michener and Lajtha, 2007). The 8^^G val¬ 
ues found in our otolith samples (Fig. 2B) indicate that 
southern waters were infiuenced by estuarine inputs 
more than waters near Rio de Janeiro. 
Genetic markers provide an important tool for iden¬ 
tifying the degree of reproductive isolation between 
groups (Gadrin et al., 2014). Nevertheless, the study 
of the life history of an individual fish through otolith 
chemistry provides fine-scale geographic differences 
that genetic studies may not be able to detect (Gonover, 
1998). In our study, there was a great advantage in 
using phenotypic methods, such as isotope analysis of 
otoliths, for identifying stocks of tainha. Because the 
growth patterns of fish groups can be different and 
strongly infiuenced by the environment (Gampana and 
Thorrold, 2001) and because fishing acts as a source of 
recent pressure on evolution (Rijnsdorp, 1993), pheno¬ 
typic methods are relevant and useful in analyses of 
fish resources. 
Isotopic analysis of 8^®0 and 8^^G in otoliths of ju¬ 
venile tainha revealed 2 stocks along the southern and 
southeastern Brazilian coasts. The results from this 
study confirm the observation of Mai et al. (2014) and 
provide a first biological explanation for the mainte¬ 
nance of genetic difference between these 2 popula¬ 
tions. Gonsidering the economic importance of this 
species for the southern coast of Brazil (from 33°S to 
26°S), managers should consider the southern stock as 
a distinct unit for management purposes. 
