Stable carbon and nitrogen isotope analysis reveals seasonal variation in the diet of leopard seals

In order to assess seasonal and spatial changes in diet, the δ 15 N and δ 13 C signatures of vibrissae from leopard seals Hydrurga leptonyx obtained from Prydz Bay, Eastern Antarctica, were compared with those of a captive seal on a known diet. Using the isotopic signatures of known prey, and those revealed by the assimilation rates of vibrissae, we constructed trophic models to estimate diet composition. Assuming that current diet was reflected only in the actively growing portion of the vibrissae, the latter were sectioned. Each section was then analysed independently. Two methods of analysis of the vibrissae isotopic data were compared in order to ascertain the best analytical approach to these data. A simple linear model and a von Bertalanffy growth model were used to esti- mate section age and vibrissae growth rates. The age predictions of the von Bertalanffy growth model allowed the existence of repeated seasonal oscillations in both δ 15 N and δ 13 C values. Temporal varia- tions in stable isotope ratios consistent with changes in source of feeding (inshore vs. offshore) and prey types were identified in the Antarctic leopard seals, but not in the captive seal. This preliminary study has possible implications for the use of vibrissae to track dietary changes over time and may serve as a tool for investigating foraging preferences of highly mobile or migratory pinniped species.

[1]  D. Siniff,et al.  Social and reproductive behavior of crabeater seals (Lobodon carcinophagus) during the austral spring , 1979 .

[2]  D. B. Siniff,et al.  The Role of the Leopard Seal in the Tropho-Dynamics of the Antarctic Marine Ecosystem , 1985 .

[3]  G. Rau,et al.  N-15/N-14 and C-13/C-12 in Weddell Sea Invertebrates: Implications for Feeding Diversity , 1991 .

[4]  K. Hobson,et al.  STABLE ISOTOPE ANALYSES OF TOOTH ANNULI REVEAL TEMPORAL DIETARY RECORDS: AN EXAMPLE USING STELLER SEA LIONS , 1998 .

[5]  F. Morel,et al.  A model of carbon isotopic fractionation and active carbon uptake in phytoplankton , 1999 .

[6]  K. Hobson,et al.  Stable carbon and nitrogen isotopic fractionation between diet and tissues of captive seals: implications for dietary reconstructions involving marine mammals , 1996 .

[7]  M. Ramsay,et al.  The effects of prolonged fasting of the body composition and reproductive success of female polar bears (Ursus maritimus) , 1995 .

[8]  T. Rogers,et al.  USE OF MIDAZOLAM/PETHIDINE AND TILETAMINE/ZOLAZEPAM COMBINATIONS FOR THE CHEMICAL RESTRAINT OF LEOPARD SEALS (HYDRURGA LEPTONYX) , 2002 .

[9]  J. Bengtson,et al.  Observations and Hypotheses Concerning the Interactions among Crabeater Seals, Leopard Seals, and Killer Whales , 1977 .

[10]  K. Kovacs,et al.  Energetics during nursing and early postweaning fasting in hooded seal (Cystophora cristata ) pups from the Gulf of St Lawrence, Canada , 1997, Journal of Comparative Physiology B.

[11]  K. Hobson,et al.  RETROSPECTIVE ISOTOPIC ANALYSES OF STELLER SEA LION TOOTH ANNULI AND SEABIRD FEATHERS: A CROSS‐TAXA APPROACH TO INVESTIGATING REGIME AND DIETARY SHIFTS IN THE GULF OF ALASKA , 2004 .

[12]  P. R. Condy,et al.  Antarctic Nutrient Cycles and Food Webs , 1985, Springer Berlin Heidelberg.

[13]  P. Rundel.  Stable Isotopes in Ecological Research , 1989, Ecological Studies.

[14]  H. Welch,et al.  Determination of trophic relationships within a high Arctic marine food web using δ13C and δ15N analysis , 1992 .

[15]  L. Tieszen,et al.  Fractionation and turnover of stable carbon isotopes in animal tissues: Implications for δ13C analysis of diet , 1983, Oecologia.

[16]  K. Hobson,et al.  Stable-Nitrogen Isotope Enrichment in Avian Tissues Due to Fasting and Nutritional Stress: Implications for Isotopic Analyses of Diet , 1993 .

[17]  C. Darimont,et al.  Intra-hair stable isotope analysis implies seasonal shift to salmon in gray wolf diet , 2002 .

[18]  K. Hobson,et al.  Stable carbon and nitrogen isotope patterns in baleen from eastern Arctic bowhead whales (Balaena mysticetus) , 1998 .

[19]  R. Michener.  Stable isotope ratios as tracers in marine aquatic food webs , 1994 .

[20]  J. Ward Testa,et al.  Notes on winter feeding of crabeater and leopard seals near the Antarctic Peninsula , 1988, Polar Biology.

[21]  D. Schell,et al.  Natural Isotope Abundances in Bowhead Whale ( Balaena mysticetus ) Baleen: Markers of Aging and Habitat Usage , 1989 .

[22]  D. Schell,et al.  Stable isotopes in southern right whale (Eubalaena australis) baleen as indicators of seasonal movements, feeding and growth , 1996 .

[23]  J. Eddington,et al.  GROWTH RATE AND SHEDDING OF VIBRISSAE IN THE GRAY SEAL, HALICHOERUS GRYPUS: A CAUTIONARY NOTE FOR STABLE ISOTOPE DIET ANALYSIS , 2004 .

[24]  G. Rau,et al.  N-15/N-14 and C-13/C-12 in Weddell Sea Birds, Seals, and Fish: Implications for Diet and Trophic Structure , 1992 .

[25]  L. France,et al.  Carbon-13 enrichment in benthic compared to planktonic algae : foodweb implications , 2006 .

[26]  Robert G. Clark,et al.  Turnover of 13C in cellular and plasma fractions of blood: implications for nondestructive sampling in avian dietary studies , 1993 .

[27]  R. Williams,et al.  Observations on food remains in faeces of elephant, leopard and crabeater seals , 1986, Polar Biology.

[28]  S. Eberhard,et al.  Post-fledging and winter migration of Adélie penguins Pygoscelis adeliae in the Mawson region of East Antarctica , 2003 .

[29]  S. Hall-Aspland,et al.  A new approach to the solution of the linear mixing model for a single isotope: application to the case of an opportunistic predator , 2005, Oecologia.

[30]  D. Schell.  Declining carrying capacity in the Bering Sea: Isotopic evidence from whale baleen , 2000 .

[31]  K. Hobson,et al.  Assessing Avian Diets Using Stable Isotopes I: Turnover of 13C in Tissues , 1992 .

[32]  B. Fry.  Food web structure on Georges Bank from stable C, N, and S isotopic compositions , 1988 .

[33]  K. Arrigo,et al.  Phytoplankton dynamics within 37 Antarctic coastal polynya systems , 2003 .

[34]  W. Richardson,et al.  Regional and seasonal feeding by bowhead whales Balaena mysticetus as indicated by stable isotope ratios , 2005 .

[35]  T. Rogers,et al.  Summer diet of leopard seals (Hydrurga leptonyx) in Prydz Bay, Eastern Antarctica , 2004, Polar Biology.

[36]  L. Bertalanffy,et al.  A quantitative theory of organic growth , 1938 .

[37]  C. T. Robbins,et al.  USE OF STABLE ISOTOPES TO DETERMINE DIETS OF LIVING AND EXTINCT BEARS , 1996 .

[38]  R. Goericke,et al.  Changes in the δ13C of surface water particulate organic matter across the subtropical convergence in the SW Indian Ocean , 1993 .

[39]  W. J. Dyer,et al.  A rapid method of total lipid extraction and purification. , 1959, Canadian journal of biochemistry and physiology.

[40]  T. Rogers,et al.  Predation of Adélie penguins (Pygoscelis adeliae) by leopard seals (Hydrurga leptonyx) in Prydz Bay, Antarctica , 1995 .

[41]  D. Schell,et al.  Growth rates of vibrissae of harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus) , 2001 .

[42]  T. Rogers,et al.  Spatial movement of adult leopard seals (Hydrurga leptonyx) in Prydz Bay, Eastern Antarctica , 2005, Polar Biology.

[43]  P. Falkowski,et al.  The effect of anthropogenic CO2 on the carbon isotope composition of marine phytoplankton , 2001 .

[44]  M. Castellini,et al.  Trophic interactions of Antarctic seals as determined by stable isotope signatures , 2004, Polar Biology.

[45]  D. Schell,et al.  Stable isotope ratios in harbor seal Phoca vitulina vibrissae: effects of growth patterns on ecological records , 2004 .