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Fishery Bulletin 115(2) 
55°W 50”W 45"W 
Figure 1 
Map of the 9 sampling sites along the coast of southern Brazil where specimens of tainha 
{Mugil liza) were collected in 2011 for this study of the use of stable isotope ratios in otoliths 
for discrimination of stocks. Sampling sites: 1) Chui, 2) Patos Lagoon Estuary, 3) Cassino 
Beach, 4) Mostardas, 5) Tramandaf, 6) Passo de Torres, 7) Laguna, 8) Pontal do Parana, and 
9) Rio de Janeiro. Abbreviations for southwest states: RJ= Rio de Janeiro, SP=Sao Paulo, 
PR=Parana, SC=Santa Catarina, and RS=Rio Grande do Sul. 
A stock of fish may consist of a single spawning 
unit, a biological population, a metapopulation, or 
various proportions of all these units (Cadrin et al., 
2014). The identification of discrete units of stocks has 
been, for a long time, a basic requirement for fisheries 
science and management (Cadrin et al., 2014). Many 
genotypic and phenotypic methods have been applied 
to identify stocks and distinguish fish populations (Ihs- 
sen et al., 1981; Cadrin et al., 2014). In recent years, 
otolith chemistry has also been used to identify groups 
successfully on the basis of the characterization of en¬ 
vironmental conditions at birth and during early life 
history stages (Campana et al., 1994; Gao et al., 2001). 
The theoretical basis behind stock identification 
that is based on otolith chemistry is that otoliths are 
deposited at, or very close to, oxygen isotopic equilib¬ 
rium with ambient seawater and thus scientists can 
create a record of the environmental changes that an 
individual fish experiences through time (Gao et al., 
2005). Carbon isotopes deposited in otoliths come from 
dissolved inorganic carbon (DIG) and animal metabo¬ 
lism, reflecting the physiological status of a fish and 
trophic changes (Thorrold et al., 1997). The combina¬ 
tion of carbon and oxygen isotopes is commonly used to 
reveal the spatial separation of fish resulting from seg¬ 
regation during spawning, and, therefore, can be used 
to define populations (Thorrold et al., 1997). 
Studies of the biology of tainha along the coast of 
Brazil have revealed differences among populations 
that occur over the distribution range of the species 
and that results from differences in various reproduc¬ 
tive parameters (Albieri and Araujo, 2010; Gonzalez- 
Castro et al., 2011; Lemos et al., 2014; Mai et al., 2014). 
For instance, Mai et al. (2014) discovered at least 2 ge¬ 
netically distinct populations between Rio de Janeiro, 
Brazil, and Mar del Plata, Argentina, that have dif¬ 
ferent reproductive patterns. The southern population 
is distributed between Argentina and Sao Paulo, Bra¬ 
zil, and there is the gradual northward migration of 
tainha from Argentina (at around 37°S) to Santa Cata¬ 
rina, Brazil (at around 26°S). This migration has been 
reported to occur during a prespawning process that 
takes place in high-salinity waters (35) and at sea-sur¬ 
face temperatures ranging from 19°C to 21°C, and peak 
spawning occurs in June (Lemos et al., 2014). About 
95% of the commercial catch of this species occurs as 
fish migrate between the Rio Grande do Sul (33°S) and 
the Santa Catarina coast (26°S) (CEPSUL^). 
A traditional and still widely held view regarding 
stock identification is that fish stocks are reproduc- 
tively isolated and their own internal dynamics can be 
identified by genetic markers of lineage (Ihssen et al., 
1981). But, the lack of a global molecular marker that 
identifies a reproductive isolation of fish (¥/aples et al., 
