The development of models of marine ecosystems in the Southern Ocean is becoming increasingly important as a means of understanding and managing impacts such as exploitation and climate change. ...Collating data from disparate sources, and understanding biases or uncertainties inherent in those data, are important first steps for improving ecosystem models. This review focuses on seals that breed in ice habitats of the Southern Ocean (i.e. crabeater seal, Lobodon carcinophaga; Ross seal, Ommatophoca rossii; leopard seal, Hydrurga leptonyx; and Weddell seal, Leptonychotes weddellii). Data on populations (abundance and trends in abundance), distribution and habitat use (movement, key habitat and environmental features) and foraging (diet) are summarised, and potential biases and uncertainties inherent in those data are identified and discussed. Spatial and temporal gaps in knowledge of the populations, habitats and diet of each species are also identified.
Two adult female leopard seals (Hydrurga leptonyx) were tagged with satellite-linked dive recorders off Queen Maud Land, Antarctica, just after moulting in mid-February. The transmitters transmitted ...for 80 and 220 days, respectively. Both seals remained within the pack ice relatively close to the Antarctic Continent until early May, when contact was lost with one seal. The one remaining seal then migrated north, to the east side of the South Sandwich Islands in 3 weeks, whereafter it headed east, until contact was lost at 55°S in early September. From mid-May to late September this animal always stayed close to the edge of the pack ice. Both seals made mostly short (<5 min) dives to depths of 10-50 m and only occasionally dove deeper than 200 m, the deepest dive recorded being 304 m. A nocturnal diving pattern was evident in autumn and early winter, while day-time diving prevailed in mid-winter. Haul out probability was highest at mid-day (about 40% in late February and more than 80% in March and April). From May till September the remaining animal mainly stayed at sea, in the vicinity of the pack ice, with only occasional haul outs. These data suggest that a portion of the adult leopard seals may spend the winter mainly in open water, off the edge of the pack ice, where they primarily hunt near the surface. In that case, it is likely that krill (Euphausia superba), as well as penguins, young crabeater seals (Lobodon carcinophaga) and a variety of fish are important prey items.
The present study investigated how concentrations of different organochlorines (OCs) vary with nutritional condition in adult harp seal (
Phoca groenlandica) females in a captive fasting experiment ...and in the wild. During the first part of this study seals in good condition (
N=5) were fasted for a period of 28 days and blood and blubber samples were collected at days 1, 14 and 28. Blubber OC concentrations remained unchanged throughout the experimental period, and were consistently significantly higher than concentrations in the blood. In contrast to blubber OC levels, blood OC levels showed a significant time-dependant increase. During the fasting experiment the seals lost an average of 24 kg of body mass, which is less than half the natural annual variation in this species in the wild. The second part of this study compared OC concentrations in blood and blubber from seals collected at prime condition before the breeding season (
N=10) with animals collected during molt when condition is poor (
N=7). The average mass difference between the two groups was more than 40 kg. Blood levels of most OCs were significantly higher in the thin seals compared with the levels found in the fat seals. These differences in blood OC concentrations were much greater than what was found during the fasting experiment. For example ∑PCB levels in the blood during the fasting experiment increased by ∼83%, while the corresponding increase in blood levels of ∑PCB between the two other samples was 720% (from 201 to 1447 ng/g lipid). Blubber levels of OCs from the animals in the wild were significantly higher in the thin seals compared with the fat animals. In addition, the blubber levels of OCs were significantly higher than blood levels of OCs only for the fat seals. This study demonstrates the extreme variability present in the concentrations of OCs in blood of seals in response to change in condition. Since the natural variation in condition is extreme during phocid seals’ annual cycles, we recommend that blood should not be used in studies of OCs where the aim of the study is to monitor OC levels for comparative purposes or time-trend analysis.
The distribution and diving behaviour of 16 adult harp seals (Pagophilus groenlandicus) from the Greenland Sea stock were studied in 1993 and 1999, using satellite-linked dive recorders (SDRs). The ...seals remained near the pack-ice edge in the Greenland Sea between breeding and moulting (April/May 1993; 6F) and during the first 7 weeks after moulting (June/July, 1999; 4F, 6M), there diving to depths of <100 m. In mid-July 1999, seven out of eight seals with active SDRs migrated into the Barents Sea, there diving to <400 m and sharing feeding grounds with the Barents Sea harp seal stock. Between September and December, six of these seals joined the eighth seal in the Denmark Strait until March 2000, there diving to depths of 100-400 m. Overall, dives were significantly deeper in the day and in winter than at night and in summer, with some regional differences. Harp seals are considered pack-ice-associated seals, but our tagged seals spent a considerable proportion of their time in open water, their distribution largely overlapping with that of capelin (Mallotus villosus).
Understanding the determinants of poorly studied species’ spatial ecology is fundamental to understanding climate change impacts on those species and how to effectively prioritise their conservation. ...Ross seals (
Ommatophoca rossii
) are the least studied of the Antarctic pinnipeds with a limited knowledge of their spatial ecology. We present the largest tracking study for this species to date, create the first habitat models, and discuss the potential impacts of climate change on their preferred habitat and the implications for conservation. We combined newly collected satellite tracking data (2016–2019:
n
= 11) with previously published data (2001:
n
= 8) from the Weddell, King Haakon VII and Lazarev seas, Antarctica, and used 16 remotely sensed environmental variables to model Ross seal habitat suitability by means of boosted regression trees for summer and winter, respectively. Five of the top environmental predictors were relevant in both summer and winter (sea-surface temperature, distance to the ice edge, ice concentration standard deviation, mixed-layer depth, and sea-surface height anomalies). Ross seals preferred to forage in waters ranging between −1 and 2°C, where the mixed-layer depth was shallower in summer and deeper in winter, where current speeds were slower, and away from the ice edge in the open ocean. Receding ice edge and shoaling of the mixed layer induced by climate change may reduce swimming distances and diving depths, thereby reducing foraging costs. However, predicted increased current speeds and sea-surface temperatures may reduce habitat suitability in these regions. We suggest that the response of Ross seals to climate change will be regionally specific, their future success will ultimately depend on how their prey responds to regional climate effects and their own behavioural plasticity.
A solitary skin lesion was found on the neck of a Weddell seal (
Leptonychotes weddellii), chemically immobilized in Queen Maud Land (70°09′S, 05°22′E) Antarctica 2001. The lesion was elevated and 3
...cm in diameter, consisting of partly fresh and partly necrotic tissue, and proliferative papilloma-like structures were seen. Electron microscopy on a biopsy from the lesion revealed typical parapoxvirus particles. Polymerase chain reaction (PCR; B2L gene) generated amplicons of approximately 594 base pairs, comparable to Orf-virus, the prototype parapoxvirus. A comparison of these B2L PCR amplicon DNA sequences with corresponding sequences from other parapoxviruses, showed that the Weddell seal virus resembled isolates from grey seal (
Halichoerus grypus) and harbour seal (
Phoca vitulina) more than parapoxvirus from red deer (
Cervus elaphus), sheep, cattle and Japanese serows (
Capricornis crispus). It is thus concluded that the Weddell seal parapoxvirus belong to the tentative seal parapoxvirus species. Since parapox and orthopoxviruses may cause similar clinical diseases, we suggest that the term sealpox should be restricted to the clinical disease, whereas seal parapoxvirus should be used when caused by a parapoxvirus, rather than the general term “sealpox virus”. This is the first verified case of parapoxvirus infection in a Weddell seal, and also the first report of any such infections in the Antarctic.
Previous studies have shown that harp seals may drink considerable amounts of seawater. The current study was undertaken to study the physiological responses to bolus administration of seawater. ...Adult harp seals (
Phoca groenlandica) were fasted without access to water for 48 h and then given 1000 or 1500 ml of seawater by a stomach tube. Changes in urine and plasma parameters were thereafter monitored for another 12–20 h. Urine production and urine excretion rate of Na
+ and Cl
− increased soon after administration and reached a maximum 3–4 h later. Urine osmolality was kept rather stable and high (∼1500 mOsm kg
−1) following seawater administration, due to a drop in urine concentration of urea that was proportional to the simultaneous increase in urine concentration of NaCl. Plasma osmolality remained at approximately 340 mOsm kg
−1, while plasma concentration of urea decreased some 20–25% due to increased excretion of urea when seawater was ingested. Despite bolus administrations of seawater of up to ∼2% of body mass, homeostasis was maintained and no ill effects observed. It is concluded that the concentrating abilities of the kidneys of harp seals are sufficient to prevent net loss of body water following seawater ingestion. Seawater ingestion may, moreover, increase urinary osmotic space and thus serve as a mechanism to excrete additional urea produced during phase I of fasting.
The levels of polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF), biphenyls (PCB) and compounds of the DDT group were determined in individual seal blubber and brain samples from ten male ...and one female harp seals caught in the Greenland Sea. No data from this region and from harp seals have been reported before. The age of the animals varied between 1 and 18 years. PCDD/PCDF concentrations in the blubber (4–10 pg/g TEQ wet weight (w.w.), Nordic model) were somewhat lower than in ringed seals from the Arctic. Non-ortho substituted PCB (CB 77,126 and 169) showed TEQ levels in the blubber which were about 4–10-times higher. CB 77 dominated in most samples, but in a few cases CB 169 was the most abundant congener. p,p′-DDE (average 760 ng/g w.w.) and di-ortho substituted PCB concentrations (2560 ng/g w.w. expressed as ΣPCB) in the blubber were comparable to those found in ringed seals from the European and Canadian Arctic. Levels of PCDD/PCDF in brain correspond to the detection limit (about. 0.1 – 0.6 pg/g w.w.) for most congeners. With one exception, PCB amounts in brain (w.w.) were one to two orders of magnitude lower. A highly significant correlation was found between age, p,p-DDE and di-ortho PCB as well as between single PCDD and coplanar PCB congeners. No relationship was observed between levels of PCDD/PCDF, age and di-ortho-PCB.
E. S. Nordoy and A. S. Blix
Grey seal pups (Halichoerus grypus) were collected at the time of weaning
(early November) and starved for 31 days at thermoneutrality. During
starvation body weight ...decreased linearly, whereas metabolic rate was
stable at 1.58 +/- 0.13 (SD) W X kg-1. Metabolic rate as related to body
weight was significantly higher (P less than 0.01) than predicted by
Kleiber (The Fire of Life, New York: Kreiger, 1975). Respiratory quotient
averaged 0.67 +/- 0.03 during the 1st wk but increased to an average of
0.76 +/- 0.04 during the final week of fasting. Body composition was
evaluated three times during starvation by use of computed tomography. The
area of blubber and skeletal muscle in three transverse (thoracic,
abdominal, pelvic) sections of the animals decreased on average 27.6 +/-
4.8 and 18.6 +/- 8.5%, respectively, from days 3 to 31 of fasting. Caloric
content of blubber and skeletal muscle was determined by bomb calorimetry,
and the caloric content of catabolized tissue was estimated. Based on this
information it was calculated that approximately 94% of the energy expended
by grey seal pups during the first 4 wk of the postweaning fast is derived
from their subcutaneous deposits of fat.
Field metabolic rate (FMR), using the doubly labelled water (DLW) method, was measured in free‐ranging adult kittiwakes (Rissa tridactyla) early and late in the chick‐rearing period at Svalbard, ...Norway. Individual variation in FMR was analysed by comparing FMR with body mass, sex, nest attendance, chick age, brood size, and basal metabolic rate (BMR). Mean FMR of kittiwakes during the chick‐rearing period was
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(SE) W kg−1, while the individual variation (calculated as coefficient of variation CV) in FMR was 24%. Sex, time spent away from the nest, age of the chicks, and brood size contributed significantly to FMR and explained 65% of the variation in FMR. The FMR increased by 32% from early until late in the chick‐rearing period. This occurred simultaneously with an increase in the time spent away from the nest. In 15 of 20 pairs, one of the mates had 15% or higher (mean of the 15 pairs,
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) FMR (W kg−1) than their partner, even though the mates spent equal amounts of time away from the nest. This indicates an intrapair conflict in FMR. The variation in total FMR of pairs was 40% less than the individual variation, and total FMR of pairs increased with age of the chicks. This indicates that the mates adjust their energy expenditure within a relatively constant FMR determined by the energy needs of the chicks. Individual variation in FMR could not be explained by variation in body mass or BMR. BMR measured late in the chick‐rearing period was 26% lower than previous measurements of BMR from the prebreeding and incubation periods. The increase in FMR and simultaneous decrease in BMR caused a 40% increase in metabolic intensity (FMR/BMR) of kittiwakes during the chick‐rearing period. It is suggested that the metabolic intensity is not a proper measure of the metabolic load in seabirds.
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