237
Various researches were conducted with the main aim of revealing diet of single
species and/or the trophic overlap between sympatric species. To achieve this, most
studies used SIMM to estimate the likely diet composition. In northern Rio de
Janeiro state, C and N isotopic values suggested that franciscanas and Guiana dolphins, two of the most common coastal dolphin species along southeastern and
southern Brazil, have a considerable overlap in their isotopic niches, despite the
larger niche areas of the latter (Di Beneditto et al. 2011; Di Beneditto & Monteiro
2015). Evidence of an overlap in diet between the two species, based on the similarity of δ
13
C and δ
15
N values, was also observed in the estuarine region of Babitonga
bay, in southern Brazil (Hardt et al. 2013). This pattern contrasts to previous stomach content studies (Cremer et al. 2012) and might be influenced by the simple
visual exploration of the isotopic values of prey and consumers in the δ-space in the
study of Hardt et al. (2013). Thus further research on this topic is needed for a better
understanding of the trophic interactions between these sympatric species in
Babitonga Bay.
Regional, seasonal and gender-related differences in the diet of dusky dolphins
were investigated in four gulfs of Peninsula Valdés, Argentina (de Castro et al.
2015). The contribution of potential prey, as inferred by SIMM, indicated an
opportunistic feeding of dusky dolphins upon pelagic items. While information
from stomach contents pointed to a predominant predation on Argentine anchovies
(Engraulis anchoita) SIA indicated butterfish (Stromateus brasiliensis) as the main
prey for dusky dolphins in this region. However, the potential of SIAR for discriminating among these items was limited due to their overlapped δ
13
C and δ
15
N
values. In addition, SIA suggested that feeding preference varies among gulfs but
not between warm and cold periods. Spatial isotope differences in the diet composition were also observed between short-beaked common dolphins from the continental shelf off Buenos Aires, where the Argentine hake (Merluccius hubbsi) was
indicated as the main prey and the inshore waters of Golfo San Matías, northern
Patagonia, where the Argentine anchovy appeared to be more important (de Castro
et al. 2016). Compared to previous stomach content analysis, SIA indicated a more
complex diet of this species, with differences in the habitat use and foraging strategies between groups.
Long-term and gender-related variation in the diet of the bottlenose dolphin in
southern Brazil was determined through stomach content analysis and δ
13
C and
δ
15
N values in tooth dentine of individuals that washed ashore in Rio Grande do Sul
state coast from 1977 to 2012 (Secchi et al. 2016). A decrease in the contribution of
the whitemouth croaker (Micropogonias furnieri) and the kingcroaker (Menticirrhus
sp.) and an increased relative importance of the largehead hairtail were observed for
the period after 1990. This was probably a consequence of the decrease in abundance of the former fish species due to intensified fishing activity in the region during recent decades. Despite a slightly higher importance of the mullet (Mugil liza)
for females, it seems that males and females share the same resources. The results
also show that bottlenose dolphins from this area are opportunistic feeders and prey
upon the most available demersal and demersal–pelagic teleost fish.
9 Using Chemical Elements to the Study of Trophic and Spatial Ecology in Marine…
Various researches were conducted with the main aim of revealing diet of single
species and/or the trophic overlap between sympatric species. To achieve this, most
studies used SIMM to estimate the likely diet composition. In northern Rio de
Janeiro state, C and N isotopic values suggested that franciscanas and Guiana dolphins, two of the most common coastal dolphin species along southeastern and
southern Brazil, have a considerable overlap in their isotopic niches, despite the
larger niche areas of the latter (Di Beneditto et al. 2011; Di Beneditto & Monteiro
2015). Evidence of an overlap in diet between the two species, based on the similarity of δ
13
C and δ
15
N values, was also observed in the estuarine region of Babitonga
bay, in southern Brazil (Hardt et al. 2013). This pattern contrasts to previous stomach content studies (Cremer et al. 2012) and might be influenced by the simple
visual exploration of the isotopic values of prey and consumers in the δ-space in the
study of Hardt et al. (2013). Thus further research on this topic is needed for a better
understanding of the trophic interactions between these sympatric species in
Babitonga Bay.
Regional, seasonal and gender-related differences in the diet of dusky dolphins
were investigated in four gulfs of Peninsula Valdés, Argentina (de Castro et al.
2015). The contribution of potential prey, as inferred by SIMM, indicated an
opportunistic feeding of dusky dolphins upon pelagic items. While information
from stomach contents pointed to a predominant predation on Argentine anchovies
(Engraulis anchoita) SIA indicated butterfish (Stromateus brasiliensis) as the main
prey for dusky dolphins in this region. However, the potential of SIAR for discriminating among these items was limited due to their overlapped δ
13
C and δ
15
N
values. In addition, SIA suggested that feeding preference varies among gulfs but
not between warm and cold periods. Spatial isotope differences in the diet composition were also observed between short-beaked common dolphins from the continental shelf off Buenos Aires, where the Argentine hake (Merluccius hubbsi) was
indicated as the main prey and the inshore waters of Golfo San Matías, northern
Patagonia, where the Argentine anchovy appeared to be more important (de Castro
et al. 2016). Compared to previous stomach content analysis, SIA indicated a more
complex diet of this species, with differences in the habitat use and foraging strategies between groups.
Long-term and gender-related variation in the diet of the bottlenose dolphin in
southern Brazil was determined through stomach content analysis and δ
13
C and
δ
15
N values in tooth dentine of individuals that washed ashore in Rio Grande do Sul
state coast from 1977 to 2012 (Secchi et al. 2016). A decrease in the contribution of
the whitemouth croaker (Micropogonias furnieri) and the kingcroaker (Menticirrhus
sp.) and an increased relative importance of the largehead hairtail were observed for
the period after 1990. This was probably a consequence of the decrease in abundance of the former fish species due to intensified fishing activity in the region during recent decades. Despite a slightly higher importance of the mullet (Mugil liza)
for females, it seems that males and females share the same resources. The results
also show that bottlenose dolphins from this area are opportunistic feeders and prey
upon the most available demersal and demersal–pelagic teleost fish.
9 Using Chemical Elements to the Study of Trophic and Spatial Ecology in Marine…