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...

Short-tailed albatross Phoebastria albatrus nesting on an egg at the main colony on Torishima, Tsubame-zaki, Japan.

Population loss is often a harbinger of species extinction, but few opportunities exist to follow a species' demography and genetics through both time and space while this occurs. Previous research has shown that the northern fur seal (Callorhinus ursinus) was extirpated from most of its range over the past 200-800 years and that some of the extirpated populations had unique life history strategies. In this study, widespread availability of subfossils in the eastern Pacific allowed us to examine temporal changes in spatial genetic structure during massive population range contraction and partial recovery. We sequenced the mitochondrial control region from 40 ancient and 365 modern samples and analyzed them through extensive simulations within a serial Approximate Bayesian Computation framework. These analyses suggest that the species maintained a high abundance, probably in subarctic refugia, that dispersal rates are likely 85% per generation into new breeding colonies, and that population structure was not higher in the past. Despite substantial loss of breeding range, this species' high dispersal rates and refugia appear to have prevented a loss of genetic diversity. High dispersal rates also suggest that previous evidence for divergent life history strategies in ancient populations likely resulted from behavioral plasticity. Our results support the proposal that panmictic, or nearly panmictic, species with large ranges will be more resilient to future disturbance and environmental change. When appropriately verified, evidence of low population structure can be powerful information for conservation decision-making.

Skipjack tuna Katsuwonus pelamis sustains the largest catches among tuna species. Despite its relevance for global food security and the tuna canning industry, information about its foraging ecology in the southwestern Atlantic Ocean (SWAO) is limited. We combined amino acid (AA) and bulk tissue nitrogen isotope (δ15N) analysis with stomach content analysis (SCA) to study skipjack foraging habitat and trophic position (TP) in the SWAO. Mean (±SD) δ15N values of source AAs lysine (Lys: 6.5 ± 1.3‰) and phenylalanine (Phe: 10.6 ± 1.3‰) were higher at higher latitudes (30-34°S) of the southern area relative to the northern area between 20-26° S (Lys: 3.4 ± 1.1‰, Phe: 8.2 ± 1.2‰). Correlations between bulk tissue δ15N (δ15Nbulk) and source AA δ15N showed that Lys is a more robust indicator of δ15N baseline variation in this region than Phe. Regional mixing models based on AA δ15N indicated spatial structure in foraging habitat: smaller individuals use the southern area and larger individuals forage at lower latitudes or in offshore areas. TP estimates using the Glx-Lys trophic-source AA pair were in much better agreement with TP estimates based on SCA (TPSCA) and on bulk tissue analysis (TPbulk) than those using Glx-Phe. Skipjack forages across multiple food webs throughout its lifecycle in the SWAO and increases its TP with ontogeny (TPGlx-Lys: 3.5-4.0). Stock management strategies should consider that the southern region supports dense aggregations of juvenile skipjack, which may be more vulnerable to non-selective fisheries.

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