244
A specific comparison of the advantage of using the SIMMsto the traditional
methods was made for two species of marine mammals, the South American fur seal
(Arctocephalus australis) and the South American sea lion (Otaria flavescens), in
Uruguay (Franco-Trecu et al. 2013). The SIMMs can include (SIMMs-IP) or not
(SIMMs-UP) some informative priors to the analysis. Both were compared to the
scat analysis of these species. The two SIMMs methods resulted in different diet
composition. Based on the SIMM-UP, the diet of the fur seals was dominated by
pelagic fishes and no clear dominance was detected for sea lions. The SIMM-IP
indicated a dominance of other fish species, including the striped weakfish
(Cynoscion guatucupa), in accordance with the scat analysis, highlighting the
importance of squids for the diet of both otariid species.
Despite the great advantages of methodologies considered here, they have limitations and care should be take when interpreting their results and estimating the diet
composition of a species. When compared to the gut content analsysis, the main
disadvantages are: (i) classification of broad cathegories of preys (not at the smaller
or species level); (ii) limited possibility of detect short-term differences/changes in
the diet of large predators (it will depended on the tissue turnover rate) and (iii)
restricted capacity of detecting spatial changes in the diet of the organisms (considerable changes in δ
13
C among areas are necessary to occour) (Polunin and Pinnegar
2002).
These limitations should be taken into consideration for the application of SIA
and for the interpretation of its results. Despite them, considerable progress have
been achieved through the use of this tool. In this chapter we presented several
examples of how the understanding on the ecology of marine mammals in the
SAO have been improved by SIA and trace elements methods. Althoug the advances
in this field are fast, such as in the use of compound-specific SIA (e.g. McMahon
et al. 2013), we hope this chapter highlights the importance of these tools and
encourage researchers to use them as well as other chemical tracers methods, such
as fatty acids, for a better understanding of the spatial and trophic ecology of marine
mammals.
References
Albernaz TL, Secchi ER, Oliveira LR et al (2016) Ontogenitic and gender-related variation
in the isotopic niche within and between three species of fur seals (genus Arctocephalus).
Hydrobiologia. doi:10.1007/s10750-016-2950-0
Albuquerque CQ, Miekeley N, Muelbert JH et al (2012) Estuarine dependency in a marine fish
evaluated with otolith chemistry. Mar Biol 159:2229–2239
Baptista G, Kehrig HA, Di Beneditto APM et al (2016) Mercury, selenium and stable isotopes
in four small cetaceans from the Southeastern Brazilian coast: influence of feeding strategy.
Environ Pollut 218:1298–1307
Barnes C, Jennings S, Barry JT (2009) Environmental correlates of large-scale spatial variation in
the δ
13
C of marine mammals. Estuar Coast Shelf Sci 81:368–374
Bearhop S, Adams CE, Waldron S et al (2004) Determining trophic niche width: a novel approach
using stable isotope analysis. J Anim Ecol 73:1007–1012
E. Seyboth et al.
A specific comparison of the advantage of using the SIMMsto the traditional
methods was made for two species of marine mammals, the South American fur seal
(Arctocephalus australis) and the South American sea lion (Otaria flavescens), in
Uruguay (Franco-Trecu et al. 2013). The SIMMs can include (SIMMs-IP) or not
(SIMMs-UP) some informative priors to the analysis. Both were compared to the
scat analysis of these species. The two SIMMs methods resulted in different diet
composition. Based on the SIMM-UP, the diet of the fur seals was dominated by
pelagic fishes and no clear dominance was detected for sea lions. The SIMM-IP
indicated a dominance of other fish species, including the striped weakfish
(Cynoscion guatucupa), in accordance with the scat analysis, highlighting the
importance of squids for the diet of both otariid species.
Despite the great advantages of methodologies considered here, they have limitations and care should be take when interpreting their results and estimating the diet
composition of a species. When compared to the gut content analsysis, the main
disadvantages are: (i) classification of broad cathegories of preys (not at the smaller
or species level); (ii) limited possibility of detect short-term differences/changes in
the diet of large predators (it will depended on the tissue turnover rate) and (iii)
restricted capacity of detecting spatial changes in the diet of the organisms (considerable changes in δ
13
C among areas are necessary to occour) (Polunin and Pinnegar
2002).
These limitations should be taken into consideration for the application of SIA
and for the interpretation of its results. Despite them, considerable progress have
been achieved through the use of this tool. In this chapter we presented several
examples of how the understanding on the ecology of marine mammals in the
SAO have been improved by SIA and trace elements methods. Althoug the advances
in this field are fast, such as in the use of compound-specific SIA (e.g. McMahon
et al. 2013), we hope this chapter highlights the importance of these tools and
encourage researchers to use them as well as other chemical tracers methods, such
as fatty acids, for a better understanding of the spatial and trophic ecology of marine
mammals.
References
Albernaz TL, Secchi ER, Oliveira LR et al (2016) Ontogenitic and gender-related variation
in the isotopic niche within and between three species of fur seals (genus Arctocephalus).
Hydrobiologia. doi:10.1007/s10750-016-2950-0
Albuquerque CQ, Miekeley N, Muelbert JH et al (2012) Estuarine dependency in a marine fish
evaluated with otolith chemistry. Mar Biol 159:2229–2239
Baptista G, Kehrig HA, Di Beneditto APM et al (2016) Mercury, selenium and stable isotopes
in four small cetaceans from the Southeastern Brazilian coast: influence of feeding strategy.
Environ Pollut 218:1298–1307
Barnes C, Jennings S, Barry JT (2009) Environmental correlates of large-scale spatial variation in
the δ
13
C of marine mammals. Estuar Coast Shelf Sci 81:368–374
Bearhop S, Adams CE, Waldron S et al (2004) Determining trophic niche width: a novel approach
using stable isotope analysis. J Anim Ecol 73:1007–1012
E. Seyboth et al.