Stable isotopes document seasonal changes in trophic niches and winter foraging individual specialization in diving predators from the Southern Ocean
Article first published online: 14 MAY 2007
Journal of Animal Ecology
Volume 76, Issue 4, pages 826–836, July 2007
How to Cite
CHEREL, Y., HOBSON, K. A., GUINET, C. and VANPE, C. (2007), Stable isotopes document seasonal changes in trophic niches and winter foraging individual specialization in diving predators from the Southern Ocean. Journal of Animal Ecology, 76: 826–836. doi: 10.1111/j.1365-2656.2007.01238.x
- Issue published online: 2 JUN 2007
- Article first published online: 14 MAY 2007
- Received 23 October 2006; accepted 28 February 2007
- fur seal;
- nonbreeding period;
- resource partitioning;
- trophic level
- 1Climatic variation outside the breeding season affects fluctuations in population numbers of seabirds and marine mammals. A challenge in identifying the underlying biological mechanisms is the lack of information on their foraging strategies during winter, when individuals migrate far from their breeding grounds.
- 2We investigated the temporal variability in resource partitioning within the guild of five sympatric Subantarctic penguins and fur seals from Crozet Islands. The stable isotopic ratios of carbon (δ13C) and nitrogen (δ15N) for whole blood were measured for penguins and fur seals, as were the isotopic ratios for penguin nails and food. Animals were sampled at two periods, during breeding in summer and at their arrival in the colonies in spring (hereafter winter, since the temporal integration of blood amounting to several months).
- 3In summer, δ13C and δ15N for blood samples defined three foraging areas and two trophic levels, respectively, characterizing four nonoverlapping trophic niches. King penguins and female Antarctic and Subantarctic fur seals are myctophid eaters foraging in distinct water masses, while both macaroni and rockhopper penguins had identical isotopic signatures indicating feeding on crustaceans near the archipelago.
- 4Isotopic ratios were almost identical in summer and winter suggesting no major changes in the species niches, and hence, in the trophic structure of the guild during the nonbreeding period. A seasonal difference, however, was the larger variances in δ13C (and also to a lesser extent in δ15N) values in winter, thus verifying our hypothesis that trophic niches widen when individuals are no longer central place foragers.
- 5Winter isotopic ratios of macaroni penguins and male Antarctic fur seals had large variances, indicating individual foraging specializations. The range of δ13C and δ15N values of male fur seals showed, respectively, that they dispersed over a wide latitudinal gradient (from Antarctica to north of the archipelago) and fed on different prey (crustaceans and fish).
- 6By comparing summer and winter isotopic ratios and examining the summer diet, we highlight the feeding habits of marine predators that were not previously addressed. The findings have a number of implications for understanding the functioning of the pelagic ecosystem and on the demography of these species.