239
(PV) were sampled every 2 cm from base to tip in order to get chronologically
ordered δ
15
N and δ
13
C values (Rowntree et al. 2001, 2008). These baleen plates
showed oscillation in δ
13
C values that corresponded to annual cycles where whales
alternate their feeding between the Patagonian continental shelf (higher δ
13
C values)
and higher latitudes areas (i.e. South Georgia, with lower δ
13
C values) (Rowntree
et al. 2008). Furthermore, differences in the range of the annual oscillations among
whales were attributed to an individual variation in the feeding grounds of specimens from PV. The combination of the stable isotope signatures and molecular
analysis of biopsy samples from PV revealed that southern right whales have a
maternally inherited site fidelity to summer foraging grounds, as isotopically similar whales shared the same haplotypes (Valenzuela et al. 2009).
Stable isotope compositions of C, N and O of bone samples of southern right
whales evidenced a significant difference in the δ
13
C and δ
18
O between PV and
southern Brazil, the two main breeding sites of the species in the SAO. In addition,
lack of significant variation in δ
15
N suggests similar trophic position of their prey
(Vighi et al. 2014). Results were in accordance with the isotope baselines of the
breeding areas used by the species, suggesting that substantially feeding occur also
in these areas.
9.2.2 Pinnipeds
The understanding on several aspects of the ecology of South American sea lion
(Otaria flavescens), fur seals (Arctocephalus spp.) and the Southern elephant seal
(Mirounga leonina) along their distribution in SAO have also been enhanced
through the use of SIA.
To investigate the influence of sealing and industrial fishing in the diet of sea
lions in northern Patagonia, Argentina, skull samples collected from 1940 and 2007
were used in the study of Drago et al. (2009a). They observed a decrease in the δ
13
C
for both males and females for the period from 1940 to 1970, indicating a decrease
in the consumption of benthic coastal preys. Then, a significant increase in δ
13
C was
detected, which was related to an increase in the predation upon pelagic prey. The
period during which a coastal feeding predominated was related to the hunting of
the species. This led to a marked population decrease, and probably the remaining
animals concentrated in the coastal area (Drago et al. 2009a). In another study with
the same species and in the same area, Drago et al. (2010) noticed that pups suckling
from females that feed on the pelagic offshore preys seem to present faster growth
rates than those that feed on the benthic coastal prey. Although preying in the coastal
region might be more convenient because it can reduce the intervals between suckling bouts (e.g. Costa 2008), preys in this region have lower energy densities than
pelagic ones (Eder and Lewis 2005). The difference in the foraging habitat among
females of this population was related to performance, which, in turn, depends on
the individual’s age, body size, and/or foraging skills (Drago et al. 2010). The overlap between the diet of male and female sea lions was also investigated trough SIA
9 Using Chemical Elements to the Study of Trophic and Spatial Ecology in Marine…
(PV) were sampled every 2 cm from base to tip in order to get chronologically
ordered δ
15
N and δ
13
C values (Rowntree et al. 2001, 2008). These baleen plates
showed oscillation in δ
13
C values that corresponded to annual cycles where whales
alternate their feeding between the Patagonian continental shelf (higher δ
13
C values)
and higher latitudes areas (i.e. South Georgia, with lower δ
13
C values) (Rowntree
et al. 2008). Furthermore, differences in the range of the annual oscillations among
whales were attributed to an individual variation in the feeding grounds of specimens from PV. The combination of the stable isotope signatures and molecular
analysis of biopsy samples from PV revealed that southern right whales have a
maternally inherited site fidelity to summer foraging grounds, as isotopically similar whales shared the same haplotypes (Valenzuela et al. 2009).
Stable isotope compositions of C, N and O of bone samples of southern right
whales evidenced a significant difference in the δ
13
C and δ
18
O between PV and
southern Brazil, the two main breeding sites of the species in the SAO. In addition,
lack of significant variation in δ
15
N suggests similar trophic position of their prey
(Vighi et al. 2014). Results were in accordance with the isotope baselines of the
breeding areas used by the species, suggesting that substantially feeding occur also
in these areas.
9.2.2 Pinnipeds
The understanding on several aspects of the ecology of South American sea lion
(Otaria flavescens), fur seals (Arctocephalus spp.) and the Southern elephant seal
(Mirounga leonina) along their distribution in SAO have also been enhanced
through the use of SIA.
To investigate the influence of sealing and industrial fishing in the diet of sea
lions in northern Patagonia, Argentina, skull samples collected from 1940 and 2007
were used in the study of Drago et al. (2009a). They observed a decrease in the δ
13
C
for both males and females for the period from 1940 to 1970, indicating a decrease
in the consumption of benthic coastal preys. Then, a significant increase in δ
13
C was
detected, which was related to an increase in the predation upon pelagic prey. The
period during which a coastal feeding predominated was related to the hunting of
the species. This led to a marked population decrease, and probably the remaining
animals concentrated in the coastal area (Drago et al. 2009a). In another study with
the same species and in the same area, Drago et al. (2010) noticed that pups suckling
from females that feed on the pelagic offshore preys seem to present faster growth
rates than those that feed on the benthic coastal prey. Although preying in the coastal
region might be more convenient because it can reduce the intervals between suckling bouts (e.g. Costa 2008), preys in this region have lower energy densities than
pelagic ones (Eder and Lewis 2005). The difference in the foraging habitat among
females of this population was related to performance, which, in turn, depends on
the individual’s age, body size, and/or foraging skills (Drago et al. 2010). The overlap between the diet of male and female sea lions was also investigated trough SIA
9 Using Chemical Elements to the Study of Trophic and Spatial Ecology in Marine…