Effecto fo el niño.......

Journal of Biogeography (J. Biogeogr.) (2008) 35, 248–256

ORIGINAL ARTICLE

˜ ˜ The effects of El Nino–La Nina on reproductive parameters of elephant seals feeding in the Bellingshausen Sea
D. F. Vergani1*, J. C. Labraga2, Z. B. Stanganelli3 and M. Dunn4

Centro de Estudios Territoriales (CET) del Chubut, Marcelo T. de Alvear 1448, Puerto Madryn, Chubut, Argentina, 2Centro Nacional ´Patagonico (CENPAT-CONICET), Boulevard Alm. Brown 3500, Puerto Madryn, Chubut, ´ Argentina, 3Direccion General de Catastro e ´ Informacion Territorial (DGCeIT), Provincia del Chubut, Alejandro Maiz 169, Rawson, Chubut, Argentina and 4Cree Regional Authority, 277 Duke Street, Montreal, Canada

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ABSTRACT

˜ ˜ Aim To assess the impacts of El Nino–La Nina events on the pup weaning mass and diet offemale southern elephant seals (Mirounga leonina) feeding in the Bellingshausen Sea, Antarctica, and to understand the ecological processes that drive these impacts. Location Atlantic southern elephant seal weaning mass and diet were measured at King George Island (62º14¢ S, 58º30¢ W). Feeding areas for pregnant female seals from King George Island are located west of Alexander Island in theBellingshausen Sea. Methods Data on weaning mass were collected between 1985 and 1994 during the breeding season (September–November). Moulting females were anaesthetized and cephalopod beaks were isolated and identified from stomach contents obtained from stomach lavages. Sea-surface temperature anomaly ˜ (SSTA) data for the ‘El Nino 3.4’ geographical region (5º N–5º S, ˜ 120º W–170º W) were used todefine El Nino–Southern Oscillation (ENSO) ˜ ˜ event years (grouped as El Nino, La Nina and Neutral) as well as the strength of each ENSO event year. Using data from the US National Center for Environmental Prediction, temperature, sea ice concentration and atmospheric pressure anomalies in the Bellingshausen Sea were calculated from March to August, corresponding to the feeding period of pregnantfemale seals. Results Positive temperature anomalies and negative pressure anomalies in the ˜ Bellingshausen Sea were observed during La Nina years and negative temperature ˜ anomalies and positive pressure anomalies during El Nino years. These data correlate with sea ice concentration anomalies, which are highly negative during ˜ ˜ La Nina years and highly positive during El Nino years. Warmtemperature ˜ a years are strongly related to conditions in the Bellingshausen Sea during La Nin both higher weaning mass in elephant seals and to an increase in squid beaks in the stomach contents of females. Main conclusions It is possible that higher elephant seal weaning masses in La ˜ Nina years correlate with warmer waters in the Bellingshausen Sea leading to the rapid growth of squid and theirmore frequent descents to depths frequented by elephant seals. This results in increased predation by pregnant females, leading to a greater mass among weaned pups. This hypothesis may guide future research about interactions between climate and the marine biosphere. Keywords Bellingshausen Sea, elephant seal, ENSO, King George Island, Mirounga leonina, Psychroteuthis glacialis, squid.*Correspondence: D. F. Vergani, Centro de Estudios Territoriales (CET) del Chubut, Marcelo T. de Alvear 1448 Puerto Madryn, Chubut Argentina. E-mail: dvergani75@hotmail.com, atlaschubut@yahoo.com

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www.blackwellpublishing.com/jbi doi:10.1111/j.1365-2699.2007.01780.x

ª 2007 The Authors Journal compilation ª 2007 Blackwell Publishing Ltd

ENSO effects on elephant seals in the Bellingshausen SeaINTRODUCTION ˜ The El Nino–Southern Oscillation (ENSO) phenomenon is considered to be a coupled instability in the ocean–atmosphere system triggered by feedback between anomalous sea-surface temperatures (SST), wind stress and convective activity in the tropical Pacific Ocean (Peixoto & Oort, 1992). This feedback system causes a seesaw effect in surface pressure differences between the east...