Two behavioural traits promote fine-scale species segregation and moderate hybridisation in a recovering sympatric fur seal population

Abstract.Since its near extermination by sealing, the New Zealand fur seal (Arctocephalus forsteri) has been recolonising areas of its former range throughout New Zealand and Australia. This study examined fur seal population growth over four breeding seasons spanning 2002–05 at the Ohau Point and Lynch’s Reef colonies in Kaikoura and the Horseshoe Bay and Te Oka Bay colonies on Banks Peninsula, on the east coast of New Zealand. Estimates of pup numbers were made using mark–recapture techniques and condition indices were used to assess the body condition of pups in each colony. We found that the Ohau Point and Te Oka Bay colonies are growing exponentially (32% and 47% per annum respectively), reaching nearly 600 pups at Ohau Point and 300 pups at Te Oka Bay, whereas Horseshoe Bay appears stable. Pups born at Ohau Point are consistently heavier and in better condition than their Banks Peninsula counterparts despite the faster rate of growth observed at Te Oka Bay. An El Niño event in 2003 coincided with a drop in mass and condition at the Banks Peninsula colonies, but not at the Kaikoura colony. This discrepancy between colonies in response to environmental conditions suggests that colony-specific variables at Kaikoura may provide more favourable conditions for rearing pups than on Banks Peninsula.

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Early sealing regimes: the Bering Sea fur seal regime vis-à-vis Finnish–Soviet fishing and sealing agreements

Polar Record ◽

10.1017/s0032247415000236 ◽

2015 ◽

Vol 52 (1) ◽

pp. 109-114 ◽

Cited By ~ 1

Author(s):

Nikolas Sellheim

Keyword(s):

Environmental Management ◽

Soviet Union ◽

Bering Sea ◽

Environmental Law ◽

Early Years ◽

The Soviet Union ◽

Fur Seal ◽

Seal Population ◽

Primary Focus ◽

The Bering Sea

ABSTRACTEnvironmental management had its early stages in the early years of the 20th century. This note contrasts the different regimes that emerged with regard to the management of seals and the seal hunt: the well-researched Bering Sea regime and the little known regimes between Finland and the Soviet Union. While the former shaped and already embedded principles of modern environmental law and has the seal population as its primary focus, the latter agreements did not make reference to the environmental dimension of the seal hunt, but must be read against the backdrop of the difficult border situations between the two countries.

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A Review of Northern Fur Seal Population Modelling

Wildlife 2001: Populations ◽

10.1007/978-94-011-2868-1_80 ◽

1992 ◽

pp. 1051-1061

Author(s):

Timothy J. Ragen ◽

Charles W. Fowler

Keyword(s):

Population Modelling ◽

Northern Fur Seal ◽

Fur Seal ◽

Seal Population

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

Wildlife Research ◽

10.1071/wr01039 ◽

2002 ◽

Vol 29 (4) ◽

pp. 363 ◽

Cited By ~ 17

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.

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Acanthocephalan infection of inshore fish in two fjords at South Georgia

Antarctic Science ◽

10.1017/s0954102092000300 ◽

1992 ◽

Vol 4 (2) ◽

pp. 197-203 ◽

Cited By ~ 6

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.

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Pup Production Following Harvest of Female Northern Fur Seals

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f81-011 ◽

1981 ◽

Vol 38 (1) ◽

pp. 84-90 ◽

Cited By ~ 43

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

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Historical dynamics of the Australian fur seal population: evidence of regulation by man?

Canadian Journal of Zoology ◽

10.1139/z03-134 ◽

2003 ◽

Vol 81 (8) ◽

pp. 1428-1436 ◽

Cited By ~ 18

Author(s):

J P.Y Arnould ◽

I L Boyd ◽

R M Warneke

Keyword(s):

Pregnancy Rate ◽

Age Distribution ◽

Stochastic Modelling ◽

Adult Survival ◽

Fur Seal ◽

Seal Population ◽

Female Survival ◽

The 1960S ◽

Independent Effects ◽

Modelling Approach

The Australian fur seal (Arctocephalus pusillus doriferus) was severely over-exploited in the 18th and 19th centuries and until relatively recently its population had remained steady at well below estimated presealing levels. However, the population is now increasing rapidly (6%20% per annum) throughout its range and there is a need to understand its dynamics in order to assess the potential extent and impact of interactions with fisheries. Age distribution (n = 156) and pregnancy rate (n = 110) were determined for adult females collected at a breeding colony on Seal Rocks, southeast Australia, in 19711972. Mean ± SE and maximum observed ages were 9.37 ± 0.41 and 20 years (n = 1), respectively. A stochastic modelling approach was used to fit an age distribution to the observed age-structure data and calculate rates of recruitment and adult survival. Annual adult female survival and recruitment rates between 1954 and 1971 were 0.478 ± 0.029 (mean ± SE) and 0.121 ± 0.007, respectively, suggesting that the population was experiencing a decline during the 1960s. The pregnancy rate increased from 78% at 3 years of age to an average of 85% between 413 years of age before significantly decreasing in older females (the oldest was 19 years of age). There was no significant effect of body mass or condition on the probability of a female being pregnant (P > 0.5 in both cases) and the nutritional burden of lactation did not appear to affect pregnancy rates or gestational performance. These findings suggest that the low survivorship was due to density-independent effects such as mortality resulting from interactions with fishers, which are known to have been common at the time. The recent increase in the population is consistent with anecdotal evidence that such interactions have decreased as fishing practices have changed.

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Growth of a fur seal population

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1977.0072 ◽

1977 ◽

Vol 279 (963) ◽

pp. 67-79 ◽

Cited By ~ 124

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.

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