Growth of a fur seal population

1977 ◽  
Vol 279 (963) ◽  
pp. 67-79 ◽  
Keyword(s):  
Age Groups ◽  
Population Increase ◽  
South Shetland Islands ◽  
First Year ◽  
South Georgia ◽  
Fur Seals ◽  
Fur Seal ◽  
Younger Age ◽  
Seal Population ◽  
Incipient Colonies

The Antarctic fur seal Arctocephalus gazella is a polygynous Otarid in which a single pup is produced annually by cows over the age of 2 years. Following exploitation to the verge of extinction, a small breeding colony was discovered at Bird Island, South Georgia, in the 1930s. Up to 10000 pups a year were produced in the early 1960s and by 1975 the figure had reached an estimated 90000. The rapid population increase has resulted in the colonization of extensive breeding areas on the adjacent mainland of South Georgia with incipient colonies springing up on more distant parts of the island, and also in the South Sandwich, South Orkney and South Shetland Islands. Age determinations from the teeth of 195 breeding cows reveal a low mean age, early first breeding and a predominance of the younger age groups relative to the age structure of a stable population of northern fur seals Callorhinus ursinus . Annual adult cow survival is estimated at 89.8%, while that of first-year animals is about 64.5%. A decline in the rate of population increase is forecast within ten years and an outline for investigating the most likely factors influencing such a change is suggested.

Acanthocephalan infection of inshore fish in two fjords at South Georgia

1992 ◽  
Vol 4 (2) ◽  
pp. 197-203 ◽  
Author(s):  
Krzysztof Zdzitowiecki ◽  
Martin G. White
Keyword(s):  
Dominant Species ◽  
Alimentary Tract ◽  
Body Cavity ◽  
The Body ◽  
South Shetland Islands ◽  
Shetland Islands ◽  
South Georgia ◽  
Species Association ◽  
Fur Seal ◽  
Seal Population

An examination of 111 fish of eight species, including 92 immature Notothenia rossii Richardson revealed nine acanthocephalan species, including four Echinorhynchida occurring in the alimentary tract and five Polymorphida in the body cavity. Echinorhynchida were much more numerous (87% specimens of 4855 collected), especially Metacanthocephalus johnstoni Zdzitowiecki (the dominant species) and Aspersentis megarhynchus (Linstow). The Polymorphida parasites of seals (three species) were more abundant than species parasitic in birds (two species). Association of most of species, (except Corynosoma bullosum (Linstow) and Echinorhynchus spp.), with the inshore (fjord) environment was confirmed. The species diversity, prevalence and density of infection increased with the size of immature N. rossii. Differences in acanthocephalan occurrence and changes with time are related to differences in host distribution and abundance. For example, the occurrence of C. arctocephali in N. rossii at South Georgia is related to the increase of the fur seal population. A list of acanthocephalans in fish at South Georgia and the South Shetland Islands (14 species in total) is included.

Conserving the oldest historic sites in the Antarctic: the challenges in managing the sealing sites in the South Shetland Islands

Polar Record ◽  
2009 ◽  
Vol 46 (1) ◽  
pp. 57-64 ◽  
Author(s):  
Michael Pearson ◽  
Ruben Stehberg ◽  
Andrés Zarankín ◽  
M. Ximena Senatore ◽  
Carolina Gatica
Keyword(s):  
South Shetland Islands ◽  
The South ◽  
Shetland Islands ◽  
Fur Seals ◽  
Fur Seal ◽  
Seal Population ◽  
Animal Activity ◽  
South Shetlands ◽  
The Antarctic ◽  
Management Issues

ABSTRACTThe fur seal population of the South Shetland Islands, Antarctica, was intensively hunted by sealers from the discovery of the islands in 1819 to the early 1820s, by which time the seal numbers were so depleted that sealing became uneconomic. Sealing was revived for both fur seals and elephant seals at several periods later in the century. Sealers were put ashore in gangs and built makeshift shelters in which to live, and also occupied caves. Many of these have been identified on the various islands of the South Shetlands, and a number have been excavated. The paper addresses some of the management issues facing the conservation of these sites, which include accelerating tourism, disturbance by scientific researchers, disturbance by animal activity, burial or erosion by drifting sand, and climate change.

scholarly journals First-Year Survival of Northern Fur Seals (Callorhinus ursinus) Can Be Explained by Pollock (Gadus chalcogrammus) Catches in the Eastern Bering Sea

2021 ◽  
Vol 9 (9) ◽  
pp. 975
Author(s):  
Jeffrey W. Short ◽  
Harold J. Geiger ◽  
Lowell W. Fritz ◽  
Jonathan J. Warrenchuk
Keyword(s):  
Bering Sea ◽  
First Year ◽  
Callorhinus Ursinus ◽  
Population Declines ◽  
Fishing Activity ◽  
Eastern Bering Sea ◽  
Fur Seals ◽  
Fur Seal ◽  
Seal Population ◽  
Pribilof Islands

The Pribilof northern fur seal (Callorhinus ursinus) herd in the eastern Bering Sea has declined by ~70% since the 1970s, for elusive reasons. Competition for pollock (Gadus chalcogramma) with the commercial fishery has been suspected as a contributing factor, but no correlative relationship between fishing activity and fur seal population declines has heretofore been demonstrated. Here, we present evidence for a moderately strong inverse relationship between fishery catches of pollock and first-year survival of fur seals, based on three different approaches to evaluation. We suspect this relationship results from the dependence of lactating female fur seals on locating dense and extensive schools of pollock near the Pribilof Islands to efficiently provide nutrition for their pups, because the pollock fishery also targets these same schools, and when fished, the remnants of these schools are fragmented and dispersed, making them more difficult for fur seals to locate and exploit. Inadequately fed pups are less likely to survive their initial independent residence at sea as they migrate south from the Pribilof Islands in the fall. Our results imply that pollock catches above ~1,000,000 t within ~300 km of the Pribilof Islands may continue to suppress first-year survival of Pribilof fur seals below the estimated equilibrium survival value of 0.50, leading to continued decline of the population.

Trends in abundance of New Zealand fur seals, Arctocephalus forsteri, at the Neptune Islands, South Australia

2002 ◽  
Vol 29 (4) ◽  
pp. 363 ◽  
Author(s):  
P. D. Shaughnessy ◽  
A. McKeown
Keyword(s):  
New Zealand ◽  
South Australia ◽  
The South ◽  
The North ◽  
Fur Seals ◽  
Fur Seal ◽  
Seal Population ◽  
Island Group ◽  
Direct Counting ◽  
New Zealand Fur Seal

At the Neptune Islands in early February 2000 at the end of the 1999–2000 pupping season, the abundance of New Zealand fur seal pups was determined using a mark–recapture technique in large colonies and by direct counting in small ones. Pups (n = 2355) were marked by clipping hair on the head to reveal light-coloured underfur. At the North Neptune group, there were 4221 pups and at the South Neptune group 1767 pups, making a total of 5988 pups for the Neptune Island group as a whole. At the North Neptune Islands, pup numbers increased by 53% since February 1993, from 2756 to 4221. For the South Neptune group, pup numbers decreased by 6.7%, from 1893 to 1767. The decrease was spread over most colonies on the island. The large increase in pup numbers at the North Neptune group indicates that the population there is in the recolonisation phase of growth; at the South Neptune group, the fur seal population is likely to be in the maturity phase, with fluctuations in size expected in the future. The Neptune Island group supports the largest aggregation of pinnipeds in Australia.

Fish in the diet of Antarctic fur seals (Arctocephalus gazella) at South Georgia during winter and spring

1996 ◽  
Vol 8 (2) ◽  
pp. 155-160 ◽  
Author(s):  
A.W. North
Keyword(s):  
Arctocephalus Gazella ◽  
South Georgia ◽  
Fur Seals ◽  
Fur Seal ◽  
Total Fish ◽  
Fish Remains ◽  
Gobionotothen Gibberifrons ◽  
Lepidonotothen Larseni ◽  
The Antarctic ◽  
Fish Otoliths

The occurrence of fish in the diet of the Antarctic fur seal (Arctocephalus gazella) at Bird Island, South Georgia was investigated by analysis of fish otoliths in scats (faeces) collected during late May to early November 1983. Of the 55 scats examined, 49 contained fish remains, and 45 contained fish otoliths. Ten fish species were represented by 415 otoliths, and 33 otoliths were too digested to be identified unequivocally. Fish size was estimated from otolith size based on published allometric equations. Four coastal notothenioid fishes dominated the fish component of the diet: Champsocephalus gunnari and Gobionotothen gibberifrons each comprised about 40% of the total fish mass; Chaenocephalus aceratus was ranked third by mass and the smaller Lepidonotothen larseni occurred in one quarter of the scats but was of lower importance in terms of mass. The length-frequency distribution of C. gunnari landed by the commercial fishery in October 1982 to June 1983 is similar to that which comprised the bulk of the diet in the present study. Compared with recent studies on the fish component of the diet in the literature, the dominance of C. gunnari is generally similar, however, there was a greater proportion of G. gibberifrons during the 1983 winter and spring than reported for recent winters.

Pup Production Following Harvest of Female Northern Fur Seals

1981 ◽  
Vol 38 (1) ◽  
pp. 84-90 ◽  
Author(s):  
Anne E. York ◽  
James R. Hartley
Keyword(s):  
Cohort Analysis ◽  
Survival Rates ◽  
Callorhinus Ursinus ◽  
Northern Fur Seal ◽  
Fur Seals ◽  
Fur Seal ◽  
Seal Population ◽  
Northern Fur Seals ◽  
Early Survival ◽  
The Difference

Female northern fur seals (Callorhinus ursinus) were harvested commercially from 1956 to 1968 and pelagic collections were taken for research purposes from 1958 to 1974. Early survival rates (birth to age 2) for males increased from an average of 0.32 before the harvest to 0.38 afterwards. Numbers of female pups whose births were precluded by the harvest are estimated for the years 1956–79; these account for about 70% of the difference between the numbers of pups actually born and the level of pup births before 1956. Estimates of the increased numbers of pups due to the increase in the early survival rates are presented for the years 1958–74.Key words: northern fur seal, population dynamics, female harvest, cohort analysis, St. Paul Island

scholarly journals LESSONS FROM THE COVID-19 THIRD WAVE IN CANADA: THE IMPACT OF VARIANTS OF CONCERN AND SHIFTING DEMOGRAPHICS

2021 ◽  
Author(s):  
Finlay A McAlister ◽  
Majid Nabipoor ◽  
Anna Chu ◽  
Douglas Lee ◽  
Lynora Saxinger ◽  
...  
Keyword(s):  
Age Groups ◽  
Vaccine Hesitancy ◽  
First Year ◽  
Third Wave ◽  
Wild Type ◽  
Lengths Of Stay ◽  
Younger Age ◽  
Canadian Provinces ◽  
Event Rates ◽  
The Impact

Importance: With the emergence of more transmissible SARSCoV2 variants of concern (VOC), there is an urgent need for evidence about disease severity and the health care impacts of VOC in North America, particularly since a substantial proportion of the population have declined vaccination thus far. Objective: To examine 30day outcomes in Canadians infected with SARSCoV2 in the first year of the pandemic and to compare event rates in those with VOC versus wild type infection. Design: Retrospective cohort study using linked healthcare administrative datasets. Setting: Alberta and Ontario, the two Canadian provinces that experienced the largest third wave in the spring of 2021. Participants: All individuals with a positive SARSCoV2 reverse transcriptase polymerase chain reaction swab from March 1, 2020 until March 31, 2021, with genomic confirmation of VOC screen positive tests during February and March 2021 (wave 3). Exposure of Interest: VOC versus wild type SARSCoV2 Main Outcomes and Measures: All-cause hospitalizations or death within 30 days after a positive SARSCoV2 swab. Results: Compared to the 372,741 individuals with SARSCoV2 infection between March 2020 and January 2021 (waves 1 and 2 in Canada), there was a shift in transmission towards younger patients in the 104,232 COVID19 cases identified in wave 3. As a result, although third wave patients were more likely to be hospitalized (aOR 1.34 [1.29 to 1.39] in Ontario and aOR 1.53 [95%CI 1.41 to 1.65] in Alberta), they had shorter lengths of stay (median 5 vs. 7 days, p<0.001) and were less likely to die within 30 days (aOR 0.66 [0.60 to 0.71] in Ontario and aOR 0.74 [0.62 to 0.89] in Alberta). However, within the third wave, patients infected with VOC (91% Alpha) exhibited higher risks of death (aOR 1.52 [1.27 to 1.81] in Ontario and aOR 1.67 [1.13 to 2.48] in Alberta) and hospitalization (aOR 1.57 [1.47 to 1.69] in Ontario and aOR 1.88 [1.74 to 2.02] in Alberta) than those with wild-type SARSCoV2 infections during the same timeframe. Conclusions and Relevance: On a population basis, the shift towards younger age groups as the COVID19 pandemic has evolved translates into more hospitalizations but shorter lengths of stay and lower mortality risk than seen in the first 10 months of the pandemic in Canada. However, on an individual basis, infection with a VOC is associated with a higher risk of hospitalization or death than the original wild type SARSCoV2; this is important information to address vaccine hesitancy given the increasing frequency of VOC infections now.

scholarly journals Changes in lichen diversity and community structure with fur seal population increase on Signy Island, South Orkney Islands

2010 ◽  
Vol 23 (1) ◽  
pp. 65-77 ◽  
Author(s):  
Sergio E. Favero-Longo ◽  
Nicoletta Cannone ◽  
M. Roger Worland ◽  
Peter Convey ◽  
Rosanna Piervittori ◽  
...  
Keyword(s):  
Ground Surface ◽  
Terrestrial Ecosystem ◽  
Environmental Parameters ◽  
Potential Effect ◽  
Population Increase ◽  
Terrestrial Vegetation ◽  
Lichen Diversity ◽  
Signy Island ◽  
Fur Seals ◽  
Fur Seal

AbstractSigny Island has experienced a dramatic increase in fur seal numbers over recent decades, which has led to the devastation of lowland terrestrial vegetation, with the eradication of moss turfs and carpets being the most prominent feature. Here we demonstrate that fur seals also affect the other major component of this region’s typical cryptogamic vegetation, the lichens, although with a lower decrease in variability and abundance than for bryophytes. Classification (UPGMA) and ordination (Principal Coordinate Analysis) of vegetation data highlight differences in composition and abundance of lichen communities between areas invaded by fur seals and contiguous areas protected from these animals. Multivariate analysis relating lichen communities to environmental parameters, including animal abundance and soil chemistry (Canonical Correspondence Analysis), suggests that fur seal trampling results in the destruction of muscicolous-terricolous lichens, including several cosmopolitan and bipolar fruticose species. In addition, animal excretion favours an increase in nitrophilous crustose species, a group which typically characterizes areas influenced by seabirds and includes several Antarctic endemics. The potential effect of such animal-driven changes in vegetation on the fragile terrestrial ecosystem (e.g. through modification of the ground surface temperature) confirms the importance of indirect environmental processes in Antarctica.

Changes in the abundance of New Zealand fur seals, Arctocephalus forsteri, in Western Australia

2000 ◽  
Vol 27 (2) ◽  
pp. 165 ◽  
Author(s):  
N. J. Gales ◽  
B. Haberley ◽  
P. Collins
Keyword(s):  
New Zealand ◽  
Western Australia ◽  
South Australia ◽  
Rate Of Change ◽  
Population Increase ◽  
Absolute Abundance ◽  
Abundance Estimate ◽  
Fur Seals ◽  
Fur Seal ◽  
Rate Of Increase

New Zealand fur seals, Arctocephalus forsteri, have been increasing in abundance in South Australia for at least the past three decades. A survey of New Zealand fur seals during the 1989/90 breeding season determined that about 20% of the Australian population bred at 16 sites in Western Australia, amounting to 1429 pups and an absolute abundance estimate of 7100 fur seals. A further survey of all fur seal colonies in Western Australia to determine current pup production and abundance estimates, and trends in pup production since the previous survey was undertaken in January 1999. Of the 17 breeding sites now known in Western Australia, 16 were surveyed and pup production had increased at all but one. The rate of change in pup production at the one unsurveyed site (West Island), was estimated as being equivalent to the mean rate of change at other sites. The estimated mean annual, exponential rate of increase (r) for all sites was 0.09, equivalent to a 9.8% annual increase in pup production and an overall increase in pup production in Western Australia of 113.3% between surveys. Total annual pup production has increased to 3090. The estimate of absolute abundance of New Zealand fur seals in Western Australia is now 15 100, in contrast to the 7100 estimated for the 1989/90 season. Mortality of pups at the time of the survey was estimated to be at least 1.3%. It is predicted that New Zealand fur seal populations will continue to increase in Western Australia. This is likely to have important management implications regarding aquaculture and fisheries activities. The increase in fur seal populations appears to be in contrast to populations of Australian sea lions, Neophoca cinerea, for which preliminary data show no evidence for a population increase. It is unknown whether the dynamics affecting these two species are related.

scholarly journals Wintertime overlaps between female Antarctic fur seals (Arctocephalus gazella) and the krill fishery at South Georgia, South Atlantic

PLoS ONE ◽  
2021 ◽  
Vol 16 (3) ◽  
pp. e0248071
Author(s):  
Connor C. G. Bamford ◽  
Victoria Warwick-Evans ◽  
Iain J. Staniland ◽  
Jennifer A. Jackson ◽  
Philip N. Trathan
Keyword(s):  
Antarctic Krill ◽  
Euphausia Superba ◽  
Arctocephalus Gazella ◽  
Habitat Models ◽  
South Georgia ◽  
Fur Seals ◽  
Fur Seal ◽  
Ice Edge ◽  
Future Work ◽  
Antarctic Fur Seals

The diet of Antarctic fur seals (Arctocephalus gazella) at South Georgia is dominated by Antarctic krill (Euphausia superba). During the breeding season, foraging trips by lactating female fur seals are constrained by their need to return to land to provision their pups. Post-breeding, seals disperse in order to feed and recover condition; estimates indicate c.70% of females remain near to South Georgia, whilst others head west towards the Patagonian Shelf or south to the ice-edge. The krill fishery at South Georgia operates only during the winter, providing the potential for fur seal: fishery interaction during these months. Here we use available winter (May to September) tracking data from Platform Terminal Transmitter (PTT) tags deployed on female fur seals at Bird Island, South Georgia. We develop habitat models describing their distribution during the winters of 1999 and 2003 with the aim of visualising and quantifying the degree of spatial overlap between female fur seals and krill harvesting in South Georgia waters. We show that spatial distribution of fur seals around South Georgia is extensive, and that the krill fishery overlaps with small, highly localised areas of available fur seal habitat. From these findings we discuss the implications for management, and future work.

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