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

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Weaning mass in southern elephant seals is highly variable, the heaviest pups being three times as heavy as the lightest ones. After weaning, pups undergo an extensive postweaning period in which they draw on their reserves. To quantify the energy expenditure during the postweaning period, changes in mass, body composition, and postweaning duration were measured in southern elephant seals at King George Island, South Shetland Islands, Antarctica. Overall, mean pup weaning mass was 154 +/- 26 kg (n=117) and did not differ between sexes. Mean minimum postweaning duration was 42.5 +/- 7.5 d. Heavier animals at weaning had lower mass-specific mass loss rates than lighter ones, and a faster depletion of body reserves was associated with a shorter postweaning period. The proportion of body mass represented by fat at weaning was 37% +/- 4% (n=47) and did not differ between sexes. Of these pups, 36 were recaptured after a mean period of 36 d after weaning. On average, total mass loss measured in these animals (39 kg) was composed of 39% water, 47% fat, and 12% protein. The composition of mass loss was not significantly different between sexes and was not related to weaning mass or total body energy reserves. However, fatter animals at weaning lost more fat per kilogram lost than thinner ones. Late in the fast, males and females appeared to be in a similar body condition. Nevertheless, the overall proportion of body mass represented by fat at this time was lower than that presented by the same animals at weaning. We estimated that during the postweaning period pups lost, on average, 30% of their mass at weaning. This comprised approximately 35% of the energy and 32% of the fat in the pup's body.

Adult male southern elephant seals instrumented in

We report a novel method of investigating foraging in marine mammals based on detecting biomarkers of strictly dietary origin in blood. Arsenobetaine (AsB), the arsenic analogue of the osmolyte glycine betaine, and trimethylamine N-oxide (TMAO), an osmolyte used by marine fish and invertebrates, were measured in plasma of lactating Weddell seals Leptonychotes weddellii during the postpartum fast and at different stages of lactation. Plasma dietary biomarker concentrations were low in early lactation ( ). In lactating females (n = 6) monitored longitudinally, plasma TMAO remained low for the first 3 wk p.p. Increases in AsB concentrations observed in late lactation were closely correlated (Pearson correlation r = 0.96, p < 0.01, n = 6) with increases in plasma insulin-like growth factor 1 (IGF1), a growth factor known to reflect nutritional status in other mammals. Two seals outfitted with time-depth recorders began regular deep diving at different times p.p. and showed corresponding differences in biomarker concentrations. Our results indicate that (1) most lactating Weddell seals at the study site (70% of 20 seals studied) feed after 3 to 4 wk p.p., (2) individual lactating Weddell seals may forage as early as 9 d p.p., and (3) some Weddell seals may consume little or no food throughout lactation. Dietary biomarkers provide a simple method for distinguishing feeding and fasting in freeliving marine mammals.

The microscopic anatomy of the eye of the Weddell seal was studied with various light and electron microscopic methods with a view to correlating morphological findings with the biology of this seal which is adapted to the extremes of the Antarctic environment and to extreme diving excursions into the lightless depths of the sea. In the retina an area centralis was found but no fovea centralis. The densely packed photoreceptors consist exclusively of highly differentiated rods, which in primates detect light at low intensity but have rather poor image discrimination. The ganglion cells are relatively scarce, suggesting a high degree of convergence of the light-sensitive cells on the ganglion cells. The pigment epithelium is almost devoid of pigment granules. The extensive tapetum lucidum is about 400-500 microm thick and is composed of about 30 layers of specialized cells. The cornea is 650 (center) to 800-900 (periphery) microm thick. Its structure and glycosaminoglycan histochemistry correspond to that of other mammals. The iridocorneal angle is unusually deep and pervaded by an elaborate trabecular meshwork, which together with a complex canal of Schlemm can be correlated with the ability to absorb large amounts of fluid. The ciliary muscle and its antagonist, the membrane of Bruch, are poorly developed, suggesting relatively poor abilities of accommodation. The combination of a well-developed tapetum lucidum, an unpigmented pigment epithelium, well-developed rods, and a high number of rods converging on only few ganglion cells is obviously an adaptation to an extreme light sensitivity, enabling the animals to make use of the little light available in the deep sea.

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