Isotopic assessment of prey and habitat preferences of a cetacean community in the southwestern South Atlantic Ocean

Abstract

We used stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope analysis to investigate the trophic ecology of 8 small cetacean species of the southwestern South Atlantic Ocean: 6 delphinids (Grampus griseus, Lagenorhynchus cruciger, L. australis, Lissodelphis peronii, Pseudorca crassidens, and Cephalorhynchus commersonii ) and 2 phocoenids (Phocoena dioptrica and P. spinipinnis). We also analyzed samples of possible prey collected from oceanic and coastal habitats adjacent to Tierra del Fuego. Cetacean bone-collagen δ 13 C and δ 15 N data revealed information on both habitat and prey preferences. We observed an isotopic continuum in which coastal species had the highest values of δ 13 C and δ 15 N (L. australis), while oceanic and southern species had the lowest values (L. cruciger and P. dioptrica), indicative of offshore foraging in cold oceanic waters near the Antarctic Convergence. Overlap in mean isotope values between C. commersonii and P. spinipinnis suggests that these species may have similar habitat and/or prey preferences. Isotope results for L. peronii, P. crassidens, and G. griseus suggest that at these latitudes (~54°S) they forage on the outer continental shelf. G. griseus show bimodal isotopic patterns, suggesting that 2 ecotypes that forage in different habitats and/or consume different prey items occur in this region of the southwestern Atlantic Ocean. The isotopic data presented here provide insight into the ecology of these cetaceans, with relevant implications for their successful management and conservation.KEY WORDS: Stable isotopes · δ 13 C · δ 15 N · Small cetaceans · Foraging areas · Food/prey · South Atlantic Ocean · Southern Ocean Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 418: [235][236][237][238][239][240][241][242][243][244][245][246][247][248] 2010 At present, foraging data for small cetaceans of the southwestern South Atlantic is based mainly on the analysis of stomach contents from stranded or incidentally captured animals (Goodall & Galeazzi 1985, Goodall & Schiavini 1995. These studies provide crucial data on general foraging preferences, but they produce only a snapshot of prey preferences and the trophic niche of each species. While some studies based on data from several animals provide somewhat complete information (Bastida et al. 1988, Schiavini et al. 1997, Koen Alonso et al. 1999, other studies are based on data from only a few individuals that stranded far from their normal distribution (Fernández et al. 2003), which may not represent an accurate characterization of the foraging habits of the species. Few studies were conducted by direct observation of live animals from ship or shore (Viddi & Lescrauwaet 2005).Furthermore, there are numerous difficulties in describing marine mammal diet via stomach content or scat analysis (Pierce et al. 2004, Sheppard & Harwood 2005. Specifically, variation in digestion rates and the identifiability of prey remains can create biased estimates of diet composition (Sheffie...

Isotopic evidence for the trade and production of exotic marine mammal bone artifacts at Chavín de Huántar, Peru

“…Marine food webs have a greater number of trophic levels leading to a higher δ 15 N in many species; studies of modern cetaceans report δ 15 N values ranging from 10.1 to 19.5 ‰ (Alter, Newsome, and Palumbi 2012;Hoekstra et al 2002;Newsome, Clementz, and Koch 2010;Ricciadelli et al 2010;Schoeninger and DeNiro 1984;Wilson et al 2013;Olin et al 2012). The archaeological sea lion bones from Viru studied by Szpak had an average δ 15 N value of 17.7±1.7 ‰, again showing the typically higher nitrogen values reported for marine mammals (Szpak, unpublished data).…”

“…These two samples showed very similar values for δ 13 C, average δ 13 C=−11.8±0.1 ‰, and are much more positive than the Chavín camelid samples. Their more positive δ 13 C values indicate either more C 4 plant consumption or consumption of aquatic organisms (Alter, Newsome, and Palumbi 2012;Newsome, Clementz, and Koch 2010;Ricciadelli et al 2010;Schoeninger and DeNiro 1984;Walker and Macko 1999;Alves-Stanley et al 2010;Smith et al 1996). For example, isotopic studies of modern cetaceans, such as Ricciadelli et al (2010), report δ 13 C values between −10.8 and −17.9 ‰, with most species averaging δ 13 C values around −13 ‰ (Ricciadelli et al 2010).…”

“…Their more positive δ 13 C values indicate either more C 4 plant consumption or consumption of aquatic organisms (Alter, Newsome, and Palumbi 2012;Newsome, Clementz, and Koch 2010;Ricciadelli et al 2010;Schoeninger and DeNiro 1984;Walker and Macko 1999;Alves-Stanley et al 2010;Smith et al 1996). For example, isotopic studies of modern cetaceans, such as Ricciadelli et al (2010), report δ 13 C values between −10.8 and −17.9 ‰, with most species averaging δ 13 C values around −13 ‰ (Ricciadelli et al 2010). Species that are capable of inhabiting freshwater, estuarine, and marine ecosystems such as bottlenose dolphins, harbor seals, and manatees have δ 13 C values that reflect the local ecology and food web that they forage within, and therefore, these species are highly variable in their δ 13 C values, with published data ranging from δ 13 C=−23.5 to −7 ‰ (although tissue types analyzed differed, see Alves-Stanley et al 2010;Lazzari Ciotti 2012;Olin et al 2012;Reich and Worthy 2006;Smith et al 1996;Wilson et al 2013).…”

Records of Risso's dolphin, Grampus griseus, in coastal waters of southern Argentina

“…Nevertheless, its isotopic similarities to inshore species such as the Burmeister's porpoise, Phocoena spinipinnis (Riccialdelli et al 2010), and several published coastal sighting records (Würsig & Würsig 1980, Reyes 2006, suggest that Risso's dolphin groups may move between inshore and offshore habitats, as noted near the Santa Catalina Islands (Shane 1995a, b) and in the NE Pacific Ocean (Leatherwood et al 1980). According to bone collagen δ 13 C and δ 15 N values analyzed in Riccialdelli et al (2010), the Risso's dolphin population in the Southwestern South Atlantic Ocean seems to prefer squid as a prey item, which has been recorded for other regions (Sekiguchi et al 1992, Cockcroft et al 1993, Blanco et al 2006. The movements observed by Shane (1995a, b) near the Santa Catalina Islands in the NE Pacific were related to feeding activities, whereas the ones registered by Leatherwood et al (1980) appeared to be related to surface temperatures.…”

“…Stable isotope analyses suggest that in the Southwestern South Atlantic, Risso's dolphin is mainly an offshore predator (Riccialdelli et al 2010), as it is in other parts of the world (Shane 1995a, b, Baird 2008, Bearzi et al 2010. Nevertheless, its isotopic similarities to inshore species such as the Burmeister's porpoise, Phocoena spinipinnis (Riccialdelli et al 2010), and several published coastal sighting records (Würsig & Würsig 1980, Reyes 2006, suggest that Risso's dolphin groups may move between inshore and offshore habitats, as noted near the Santa Catalina Islands (Shane 1995a, b) and in the NE Pacific Ocean (Leatherwood et al 1980).…”