238
Studies focusing on ontogenetic changes in habitat use and/or feeding habits,
including those associated with the weaning process in cetaceans have been largely
benefited from the application of SIA (Knoff et al. 2008; Newsome et al. 2009). In
the SAO, the ontogenetic differences in diet and/or weaning ages of bottlenose dolphins (Fruet et al. 2015), franciscanas (Troina et al. 2016), false killer whales
(Riccialdelli et al. 2015), Commerson’s dolphins (Riccialdelli et al. 2013) and southern right whales (Eubalaena australis [Rowntree et al. 2008]) were reported. Stable
isotopes have been successfully applied to estimate the weaning age in some cetaceans (e.g. killer whales [Newsome et al. 2009], beluga whales, Delphinapterus
leucas [Matthews and Ferguson 2015]). The rational for this approach is based on
the fact that offsprings nursing on their mother’s milk will present higher δ
15
N relative to the mother’s signal because it is produced by catabolism of her own tissues.
Likewise, they should also present lower δ
13
C values due to the influence of high
lipid content of milk and, consequently,
13
C-depleted δ
13
C values (Hobson and
Sease 1998; Newsome et al. 2009). In this context, the time of weaning can be
defined as the age when a change in trend of δ
13
C (i.e., a marked increase followed
by a stabilizing or reduction phase) and δ
15
N (i.e., a marked decrease followed by a
stabilizing or increasing phase) is detected (Newsome et al. 2009). This approach
was used based on isotopic values from tooth dentine of known-age bottlenose dolphins from the Patos Lagoon estuary and adjacent coastal areas. Trends in stable
isotope values showed a clear change in the δ
13
C and δ
15
N profiles near age 2 indicating the most probable weaning age (Fruet et al. 2015). Following the same rationale, trends in C and N stable isotope values in tooth dentine of franciscana dolphins
from southern Brazil, were positively (δ
13
C) and negatively (δ
15
N) related to age, a
pattern attributed to lactation, also in this species (Troina et al. 2016). However, the
authors highlighted the need of caution due to the fact that the amount of dentin
deposited during the first year of life in this species’ tooth is larger than that deposited later in life, then having a great contribution to the total tooth composition
and leading to inaccurate estimations of the age at weaning. Bone collagen from
Commerson’s dolphins and false killer whales from sub Antarctic regions have been
also analyzed to determine their stable isotopic composition (Riccialdelli et al.
2013, 2015). Although Commerson’s dolphins from all age classes seem to use the
same foraging areas in Tierra del Fuego, juveniles consume higher proportions of
Falkand sprats (Sprattus fueguensis) than adults while the latter consume more
cephalopods such as the Argentine shortfin squid (Illex argentinus) and the
Patagonian squid (Loligo gahi) as evidenced by SIMM (Riccialdelli et al. 2013).
Similarly, false killer whales from a mass stranding in the Strait of Magellan showed
a trend of increased C and N isotopic values between young and older age classes
(Riccialdelli et al. 2015). Both studies found relatively high δ
15
N and low δ
13
C values in calves, attributing this to their lactation period.
Although southern right whales have been studied since 1970s in Argentina and
since 1986 in Brazil, much about its spatial and trophic ecology remain unknown.
SIA has contributed to the understanding of some aspects of the species’ distribution and indicated the existence of different feeding grounds of southern right
whales. Baleen plates from adult and sub-adult right whales from Península Valdés
E. Seyboth et al.
Studies focusing on ontogenetic changes in habitat use and/or feeding habits,
including those associated with the weaning process in cetaceans have been largely
benefited from the application of SIA (Knoff et al. 2008; Newsome et al. 2009). In
the SAO, the ontogenetic differences in diet and/or weaning ages of bottlenose dolphins (Fruet et al. 2015), franciscanas (Troina et al. 2016), false killer whales
(Riccialdelli et al. 2015), Commerson’s dolphins (Riccialdelli et al. 2013) and southern right whales (Eubalaena australis [Rowntree et al. 2008]) were reported. Stable
isotopes have been successfully applied to estimate the weaning age in some cetaceans (e.g. killer whales [Newsome et al. 2009], beluga whales, Delphinapterus
leucas [Matthews and Ferguson 2015]). The rational for this approach is based on
the fact that offsprings nursing on their mother’s milk will present higher δ
15
N relative to the mother’s signal because it is produced by catabolism of her own tissues.
Likewise, they should also present lower δ
13
C values due to the influence of high
lipid content of milk and, consequently,
13
C-depleted δ
13
C values (Hobson and
Sease 1998; Newsome et al. 2009). In this context, the time of weaning can be
defined as the age when a change in trend of δ
13
C (i.e., a marked increase followed
by a stabilizing or reduction phase) and δ
15
N (i.e., a marked decrease followed by a
stabilizing or increasing phase) is detected (Newsome et al. 2009). This approach
was used based on isotopic values from tooth dentine of known-age bottlenose dolphins from the Patos Lagoon estuary and adjacent coastal areas. Trends in stable
isotope values showed a clear change in the δ
13
C and δ
15
N profiles near age 2 indicating the most probable weaning age (Fruet et al. 2015). Following the same rationale, trends in C and N stable isotope values in tooth dentine of franciscana dolphins
from southern Brazil, were positively (δ
13
C) and negatively (δ
15
N) related to age, a
pattern attributed to lactation, also in this species (Troina et al. 2016). However, the
authors highlighted the need of caution due to the fact that the amount of dentin
deposited during the first year of life in this species’ tooth is larger than that deposited later in life, then having a great contribution to the total tooth composition
and leading to inaccurate estimations of the age at weaning. Bone collagen from
Commerson’s dolphins and false killer whales from sub Antarctic regions have been
also analyzed to determine their stable isotopic composition (Riccialdelli et al.
2013, 2015). Although Commerson’s dolphins from all age classes seem to use the
same foraging areas in Tierra del Fuego, juveniles consume higher proportions of
Falkand sprats (Sprattus fueguensis) than adults while the latter consume more
cephalopods such as the Argentine shortfin squid (Illex argentinus) and the
Patagonian squid (Loligo gahi) as evidenced by SIMM (Riccialdelli et al. 2013).
Similarly, false killer whales from a mass stranding in the Strait of Magellan showed
a trend of increased C and N isotopic values between young and older age classes
(Riccialdelli et al. 2015). Both studies found relatively high δ
15
N and low δ
13
C values in calves, attributing this to their lactation period.
Although southern right whales have been studied since 1970s in Argentina and
since 1986 in Brazil, much about its spatial and trophic ecology remain unknown.
SIA has contributed to the understanding of some aspects of the species’ distribution and indicated the existence of different feeding grounds of southern right
whales. Baleen plates from adult and sub-adult right whales from Península Valdés
E. Seyboth et al.