241
was that the diet of the males of these species changed in the last years as a response
of the high fishing effort in their foraging habitats. No change was observed in the
δ
13
C and δ
15
N values of fur seals collected from 1994 to 2011 and of sea lions from
1986 to 2009 in Brazil. Vales et al. (2013) also pointed small pelagic fish and squid
as important prey for fur seals and Zenteno et al. (2014) observed that sea lions had
a mixed diet of pelagic and demersal fish along the study period.
On a larger time scale, the diet of sea lions was also reconstructed since the late
Holocene from stable isotope composition of bones remains collected from archeological sites in Patagonia (Zenteno et al. 2015). The main finds were that the trophic
levels of sea lion increased during this long time period and that the modern diet of
the species includes more benthic prey than in the past. The results also indicated
that the main changes in the species’ diet occurred in the twentieth century, after the
considerable removal of individuals by sealing, leading them to use other food
sources and then expanding their trophic niche.
Saporiti et al. (2014) conducted a study to evaluate the influence of anthropogenic activities in the structure of coastal marine food webs in the Argentinian
Patagonia. It was expected that these activities, such as sealing and fishing, shortened the food webs by the preferential removal of top predators. However, the
results showed that the modern food webs in the region are longer and less overlapping than those from ancient times. The authors attributed this to the great impact of
sealing rather than to the fishing activity. It means that the seals significantly
decreased in number and, although the fishes were affected by fishery, the size of the
fishes preyed by the seals did not change significantly over time. Consequently, the
intraspecific competition in South American fur seal diminished while they continue to have access to large-sized fish prey.
Ontogenetic changes in the diet of males South American fur seals were observed
in the Argentinian Patagonia (Vales et al. 2015). Besides the expected higher δ
15
N
and lower δ
13
C values found in pups, this study also found differences in the diet of
subsequent age classes. Juveniles seemed to feed more on pelagic and lower trophic
level prey than both sub-adults and adults, for which the Argentine shortfin squid
was considered the main prey item. These findings corroborated previous studies
that used traditional methods for diet analysis and classified A. australis in Patagonia
as a trophic generalist, despite its preference for pelagic prey. Also, it pointed to the
importance of the lobster krill (Munida gregaria), in the diet of adults, which was
only perceived through SIA method. In addition, as no regular oscillation in the
isotope values was detected in the vibrissae of the animals, the authors considered
them as no regularly migratory, although displacements of relatively small magnitude could not be ruled out (Vales et al. 2015).
Intra- and interspecific differences in spatial and trophic ecology of three species
of the genus Arctocephalus (A. australis, A. tropicalis and A. gazella, South
American fur seal, Subantarctic fur seal and Antarctic fur seal, respectivelly) were
investigated through the analysis of δ
13
C and δ
15
N values in the dentine of each
annual growth layer group (Albernaz et al. 2016). Ontogenetic variation was
observed in the diet of the three species. The results also indicated that the intra- and
interspecific competition is minimized due to the spatial and trophic segregation in
their foraging.
9 Using Chemical Elements to the Study of Trophic and Spatial Ecology in Marine…
was that the diet of the males of these species changed in the last years as a response
of the high fishing effort in their foraging habitats. No change was observed in the
δ
13
C and δ
15
N values of fur seals collected from 1994 to 2011 and of sea lions from
1986 to 2009 in Brazil. Vales et al. (2013) also pointed small pelagic fish and squid
as important prey for fur seals and Zenteno et al. (2014) observed that sea lions had
a mixed diet of pelagic and demersal fish along the study period.
On a larger time scale, the diet of sea lions was also reconstructed since the late
Holocene from stable isotope composition of bones remains collected from archeological sites in Patagonia (Zenteno et al. 2015). The main finds were that the trophic
levels of sea lion increased during this long time period and that the modern diet of
the species includes more benthic prey than in the past. The results also indicated
that the main changes in the species’ diet occurred in the twentieth century, after the
considerable removal of individuals by sealing, leading them to use other food
sources and then expanding their trophic niche.
Saporiti et al. (2014) conducted a study to evaluate the influence of anthropogenic activities in the structure of coastal marine food webs in the Argentinian
Patagonia. It was expected that these activities, such as sealing and fishing, shortened the food webs by the preferential removal of top predators. However, the
results showed that the modern food webs in the region are longer and less overlapping than those from ancient times. The authors attributed this to the great impact of
sealing rather than to the fishing activity. It means that the seals significantly
decreased in number and, although the fishes were affected by fishery, the size of the
fishes preyed by the seals did not change significantly over time. Consequently, the
intraspecific competition in South American fur seal diminished while they continue to have access to large-sized fish prey.
Ontogenetic changes in the diet of males South American fur seals were observed
in the Argentinian Patagonia (Vales et al. 2015). Besides the expected higher δ
15
N
and lower δ
13
C values found in pups, this study also found differences in the diet of
subsequent age classes. Juveniles seemed to feed more on pelagic and lower trophic
level prey than both sub-adults and adults, for which the Argentine shortfin squid
was considered the main prey item. These findings corroborated previous studies
that used traditional methods for diet analysis and classified A. australis in Patagonia
as a trophic generalist, despite its preference for pelagic prey. Also, it pointed to the
importance of the lobster krill (Munida gregaria), in the diet of adults, which was
only perceived through SIA method. In addition, as no regular oscillation in the
isotope values was detected in the vibrissae of the animals, the authors considered
them as no regularly migratory, although displacements of relatively small magnitude could not be ruled out (Vales et al. 2015).
Intra- and interspecific differences in spatial and trophic ecology of three species
of the genus Arctocephalus (A. australis, A. tropicalis and A. gazella, South
American fur seal, Subantarctic fur seal and Antarctic fur seal, respectivelly) were
investigated through the analysis of δ
13
C and δ
15
N values in the dentine of each
annual growth layer group (Albernaz et al. 2016). Ontogenetic variation was
observed in the diet of the three species. The results also indicated that the intra- and
interspecific competition is minimized due to the spatial and trophic segregation in
their foraging.
9 Using Chemical Elements to the Study of Trophic and Spatial Ecology in Marine…