Southern elephant seal movements and Antarctic sea ice

Abstract

ObjectiveSatellite telemetry was used to investigate the migratory behaviour of southern elephant seals (Mirounga leonina). The seal studies were part of the German-Argentinean cooperation project and carried out at Stranger Point on King George Island between September 1996 and February 1997. Stranger Point (62°14'S; 58°40'W) is the southernmost breeding site of elephant seals. Elephant seals are able to dive to depths in excess of 1500 m and feed on squid and fish. The objective of this study was to identify the wintering areas and feeding grounds of elephant seals of this true Antarctic breeding colony. The results can potentially be compared between years or sites, in order to monitor differences in migratory and foraging behaviour that can be attributed to environmental changes in physical parameters (e.g. sea ice distribution) or to human impact on prey resources of these top predators. Field methodsAdult female elephant seal with satellitelinked dive recorder (SDR). SDRs were glued to the hair on the backs of 7 two month-old juveniles and on the heads of 13 moulted cows. To attach the instruments, seals were sedated with a combination of ketamine, xylazin, and diazepam. The initial doses of the drugs were either administered by hand (juveniles) or by a dart gun (adults) with automatically evacuating syringes. To maintain an immobilization of 1.5 to 3 h, small additional doses of ketamine and/or diazepam were administered by hand while the transmitters were being attached and the epoxy resin allowed to set.Satellite-linked dive recorder. Two types of ARGOS (CLS/Service Argos, Toulouse, France) transmitters were used in this study: 1) Satellite transmitters (ST-10 Telonics, Mesa, AZ, USA) are designed to provide the seals' at-sea locations. 2) In addition to transmissions of locations, satellite-linked dive recorders (SDR T-6 Wildlife Computers, Redmond, WA, USA) also process data on dive depths in the form of histograms. The histograms are encoded into messages and transmitted to a polar-orbiting satellite. The accessed data provide the horizontal extent of the seals' migrations and the distribution of their dive depths. Results and DiscussionComputer animation: To obtain a comprehensive picture of the seal's foraging activity in its three-dimensional marine environment the data need to be interpreted in the context of both biological and physical parameters. In our first attempt, a computer animation was developed to relate the animals behaviour to sea ice cover. A QuickTime (Apple Computer, Inc.) animation shows the tracks of the satellite tagged elephant seals in conjunction with seasonal changes in sea ice cover in the Antarctic Peninsula region from

Cephalopoda as prey of juvenile Southern elephant seals at Isla 25 de Mayo/King George, South Shetland Islands

“…Moreover, a differential response of female and male individuals to this temporal variation was observed. While satellite telemetry studies have not indicated sexual segregation in the foraging areas of juvenile males and females of this colony (Bornemann et al, 2000(Bornemann et al, ), daneri et al (2000(Bornemann et al, , 2014 reported gender differences in the cephalopod diet of the adult component of the population, with octopod prey becoming more important in males. The interannual differences observed in the composition of the diet of juveniles of M. leonina could be linked to temporal changes in the availability of prey, mainly krill (Euphausia superba) in the feeding areas.…”

“…Another explanation might be associated to more northerly feeding grounds of juveniles which may reach the Antarctic Polar Front or even further north. In this regard Bornemann et al (2000) reported one juvenile (underyearling) elephant seal from Isla 25 de Mayo which traversed the Drake Passage and almost reached the patagonian shelf when the satellite transmitter failed.…”

“…If we consider that: (a) The juvenile seals sampled in the present study belong to the southernmost breeding population of M. leonina; (b) studies of movements at sea by satellite tellemetry of juvenile seals from this colony had shown that most of them travelled to the southwest of the South Shetland islands and centred their foraging activities in ice free areas west of the Antarctic peninsula (Bornemann et al, 2000;toSh et al, 2009). Then, the almost exclusively Antarctic distribution of their cephalopod prey taxa is probably a refl ection of their foraging areas and not a bias from the sampling technique.…”

“…25 de Mayo population of M. leonina, studies have reported that juveniles (in their first year of life), females and adult males develop their foraging activity in different areas of the Southern Ocean (Bornemann et al, 2000;toSh et al, 2009). Additionally, dietary studies conducted to date on this population, have shown that its diet differs from those of other colonies since it is mainly represented by fish and squid species distributed almost entirely south of the Antarctic Polar Front (daneri et al, 2000daneri & carlini, 2002;PiatkowSki et al, 2002).…”

Humans and the Southern Elephant Seal Mirounga leonina

“…This implies that many of the prey species are at these depths and overlap of M. leonina with commercial surface squid jigging and shallow water trawl fisheries should be minimal while use of the current fishing gear is continued. The situation is likely to be different for each population sector as fish species and their proportions are different and the various M. leonina age classes feed in different areas (Bornemann et al 2000). In that paper, foraging locations of weaned pups from King George Island are different to those of adult females.…”