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Articoli di riviste sul tema "Southern fur seals Ecology South Africa"
1
Brunner, S., P. D. Shaughnessy e M. M. Bryden. "Geographic variation in skull characters of fur seals and sea lions (family Otariidae)". Australian Journal of Zoology 50, n. 4 (2002): 415. http://dx.doi.org/10.1071/zo01056.
Testo completoAbstract (sommario):
Geographic variation was observed in skulls of several otariid species, with a general change in size corresponding with a change in latitude and primary productivity. The largest specimens were from cool temperate localities, conforming mostly to Rensch's rule. Skulls of Australian sea lions from Western Australia were generally smaller in condylobasal length, but were more robust than those from South Australia. The subantarctic fur seal did not conform to Bergmann's rule: skulls from Amsterdam Island (37�55´S) were largest, those from Gough Island (40�20´S) intermediate and those from Marion Island (46�55´S) the smallest. For both sexes, skulls of southern sea lions from the Falkland Islands were smaller than their equivalents from mainland South America. Similarly, skulls of South African fur seals from south-east South Africa appeared smaller than those from the west coast of South Africa and Namibia; skulls from Namibia grouped separately from those of south-east and west coast, South Africa. We postulate that the Otariidae are in the process of species divergence, much of which may be driven by local factors, particularly latitude and resources.
2
Kirkman, S. P., D. P. Costa, A. L. Harrison, P. G. H. Kotze, W. H. Oosthuizen, M. Weise, J. A. Botha e J. P. Y. Arnould. "Dive behaviour and foraging effort of female Cape fur seals Arctocephalus pusillus pusillus". Royal Society Open Science 6, n. 10 (ottobre 2019): 191369. http://dx.doi.org/10.1098/rsos.191369.
Testo completoAbstract (sommario):
While marine top predators can play a critical role in ecosystem structure and dynamics through their effects on prey populations, how the predators function in this role is often not well understood. In the Benguela region of southern Africa, the Cape fur seal ( Arctocephalus pusillus pusillus ) population constitutes the largest marine top predator biomass, but little is known of its foraging ecology other than its diet and some preliminary dive records. Dive information was obtained from 32 adult females instrumented with dive recorders at the Kleinsee colony (29°34.17′ S, 16°59.80′ E) in South Africa during 2006–2008. Most dives were in the depth range of epipelagic prey species (less than 50 m deep) and at night, reflecting the reliance of Cape fur seals on small, vertically migrating, schooling prey. However, most females also performed benthic dives, and benthic diving was prevalent in some individuals. Benthic diving was significantly associated with the frequency with which females exceeded their aerobic dive limit. The greater putative costs of benthic diving highlight the potential detrimental effects to Cape fur seals of well-documented changes in the availability of epipelagic prey species in the Benguela.
3
Brunner, S. "Cranial morphometrics of the southern fur seals Arctocephalus forsteri and A. pusillus (Carnivora : Otariidae)". Australian Journal of Zoology 46, n. 1 (1998): 67. http://dx.doi.org/10.1071/zo97020.
Testo completoAbstract (sommario):
The identification and classification of unknown specimens of Arctocephalus from regions of Australasia has proven difficult. Skulls from the New Zealand fur seal (Arctocephalus forsteri) and the Australian fur seal (A. pusillus doriferus), and data from specimens of the South African fur seal (A. p. pusillus), were examined. A visual method was devised to identify and separate A. p. doriferus from A. forsteri for both sexes and for most physiological age-groups. A statistical method for morphometric separation of these species was applied to adult specimens. Characteristics of males and females for both species fell into two broad categories: sexually dimorphic – mainly those characters that increase the ability of males to hold and defend territories; and non-dimorphic – those of functional importance. Studies of geographical variation showed that adult male A. forsteri from Australia were generally larger than those from Macquarie Island and New Zealand. Characteristics of A. p. doriferus were generally larger than those of A. p. pusillus. Nine specimens of New Zealand fur seals were morphologically different from the typical A. forsteri, which indicates the presence of extreme outliers or hybrids in the sample.
4
Botha, JA, SP Kirkman, JPY Arnould, AT Lombard, GJG Hofmeyr, MA Meÿer, PGH Kotze e PA Pistorius. "Geographic variation in at-sea movements, habitat use and diving behaviour of female Cape fur seals". Marine Ecology Progress Series 649 (10 settembre 2020): 201–18. http://dx.doi.org/10.3354/meps13446.
Testo completoAbstract (sommario):
Knowledge of animal foraging behaviour has implications for management and conservation. While Cape fur seals Arctocephalus pusillus pusillus comprise a major proportion of the southern African marine predator biomass, little is known about their at-sea movements. We investigated foraging distribution, habitat use and diving behaviour for 35 adult female Cape fur seals from 3 breeding colonies experiencing contrasting oceanographic regimes. Animals from Black Rocks, the smallest and eastern-most colony, undertook shorter foraging trips and utilised shallower waters over the shelf. In comparison, animals from the larger west coast colonies, at Kleinsee and False Bay, travelled further and utilised deeper shelf and shelf-slope waters. However, across colonies, females typically preferred depths of <500 m and slopes of <5°. Kleinsee and False Bay seals selected sea surface temperatures within the range typically preferred by pelagic prey species such as round herring, sardine and anchovy (14-19°C). Black Rocks individuals showed bimodal preferences for colder (16°C) and warmer waters (>22°C). Dive behaviour was similar between Kleinsee and False Bay individuals (unavailable from Black Rocks), with both pelagic and benthic foraging evident. Diel patterns were apparent at both sites, as dive depth and benthic diving increased significantly during daylight hours, likely reflecting vertical movements of prey species. We provide the first assessment of Cape fur seal movement behaviour for the South African component of the population. Observed geographic differences likely reflect the availability of suitable habitat but may also indicate differences in foraging strategies and density-dependent effects throughout the range of this species.
5
WICKENS, P. A. "Fur seals and lobster fishing in South Africa". Aquatic Conservation: Marine and Freshwater Ecosystems 6, n. 3 (settembre 1996): 179–86. http://dx.doi.org/10.1002/(sici)1099-0755(199609)6:3<179::aid-aqc184>3.0.co;2-n.
Testo completo
6
Harcourt, Robert. "Individual variation in predation on fur seals by southern sea lions (Otaria byronia) in Peru". Canadian Journal of Zoology 71, n. 9 (1 settembre 1993): 1908–11. http://dx.doi.org/10.1139/z93-273.
Testo completoAbstract (sommario):
Southern sea lions (Otaria byronia) were observed to prey on juvenile and adult female South American fur seals (Arctocephalus australis) at Punta San Juan, Peru (15°22′S, 75°12′W) between October 1987 and December 1988. Over the course of the study there were 165 attacks on fur seals with 33 seals killed. While both adult male and subadult male sea lions captured and killed fur seals, adult female and juvenile sea lions never acted aggressively towards fur seals. Adult males attacked fur seals on 82.4% of the occasions when they were present at the rookery, subadults on 52% of occasions. Distinctive pelage characteristics allowed some of the male sea lions to be individually identified, and differences in hunting success were observed between adults and subadults, and between five identifiable adults who hunted on at least five occasions. Motivation for attacks differed for subadults and adults, with subadult males using captured fur seals as female sea lion substitutes, guarding them from others and copulating with them, whilst adult sea lions hunted fur seals as food. However, only a small proportion of adult sea lions hunted fur seals, and with differing rates of success.
7
Shaughnessy, Peter D., Catherine M. Kemper, David Stemmer e Jane McKenzie. "Records of vagrant fur seals (family Otariidae) in South Australia". Australian Mammalogy 36, n. 2 (2014): 154. http://dx.doi.org/10.1071/am13038.
Testo completoAbstract (sommario):
Two fur seal species breed on the southern coast of Australia: the Australian fur seal (Arctocephalus pusillus doriferus) and the New Zealand fur seal (A. forsteri). Two other species are vagrants: the subantarctic fur seal (A. tropicalis) and the Antarctic fur seal (A. gazella). We document records of vagrant fur seals in South Australia from 1982 to 2012 based primarily on records from the South Australian Museum. There were 86 subantarctic fur seals: 49 specimens and 37 sightings. Most (77%) were recorded from July to October and 83% of all records were juveniles. All but two specimens were collected between July and November. Sightings were prevalent during the same period, but there were also nine sightings during summer (December–February), several of healthy-looking adults. Notable concentrations were near Victor Harbor, on Kangaroo Island and Eyre Peninsula. Likely sources of subantarctic fur seals seen in South Australia are Macquarie and Amsterdam Islands in the South Indian Ocean, ~2700 km south-east and 5200 km west of SA, respectively. There were two sightings of Antarctic fur seals, both of adults, on Kangaroo Island at New Zealand fur seal breeding colonies. Records of this species for continental Australia and nearby islands are infrequent.
8
Wickens, P. "Conflict between Cape (South African) fur seals and line fishing operations". Wildlife Research 23, n. 1 (1996): 109. http://dx.doi.org/10.1071/wr9960109.
Testo completoAbstract (sommario):
Cape (South African) fur seals (Arctocephalus pusillus pusillus) interact with line-fishermen in South Africa, particularly during fishing for the migratory species snoek (Thyrsites atun), and mostly when snoek are specifically being targeted. Loss of fish and tackle as a result of seals is estimated to be between at least a half and one million Rand (A$l75000-372000) annually or 3.3-7% of the total annual landed value of snoek. The presence of seals may also disturb fishing operations by causing fish to sound although this is difficult to quantify. Deliberate killing of seals by fishermen during line-fishing occurs indiscriminately and particularly during the peak snoek fishing period; however, estimation of this mortality is currently impossible.
9
Townrow, K., e P. D. Shaughnessy. "Fur seal skull from sealers' quarters at Sandy Bay, Macquarie Island, Southern Ocean". Polar Record 27, n. 162 (luglio 1991): 245–48. http://dx.doi.org/10.1017/s0032247400012651.
Testo completoAbstract (sommario):
AbstractFur seals were exterminated from Macquarie Island about 20 years after discovery of the island in 1810. Their specific identity is unknown. Few fur seals were reported at the island until it was occupied by the Australian National Antarctic Research Expeditions in 1948. Fur seal numbers are now increasing. An archaeological excavation at a sealers' quarters at Sandy Bay in 1988 revealed the fragmented skull of a young Antarctic fur sealArctocephalus gazella1.1 m below the surface in a layer dated in the 1870s and 1880s. This period coincides with the recovery of fur seal populations in the South Atlantic Ocean following earlier harvesting. Elsewhere it has been argued that the Antarctic fur seal is unlikely to have been the original fur seal at Macquarie Island because few individuals of that species are ashore in winter, which is the season when the island was discovered and fur-seal harvesting began. It is concluded that the Sandy Bay skull is from a vagrant animal.
10
Ling, JK. "Impact Of Colonial Sealing On Seal Stocks Around Australia, New Zealand And Subantarctic Islands Between 150 And 170 Degrees East". Australian Mammalogy 24, n. 1 (2002): 117. http://dx.doi.org/10.1071/am02117.
Testo completoAbstract (sommario):
Details of southern elephant seal oil and fur seal and sea lion skin cargoes have been extracted from a large number of secondary sources dealing with Australian and New Zealand maritime history, which in turn referred to numerous primary sources of information. The data were collated and analysed for ten areas in the south-west Pacific region and published recently in two separate larger works. This review is a synthesis and analysis of the impact of the colonial sealing industry on seal stocks in the region, based on those papers, with some minor revisions and reference to works by other authors. Colonial sealing lasted from the late 18th to the mid- 19th century and was followed by sporadic hunting until the late 1940s. Southern elephant seals (Mirounga leonina) were hunted for their oil; and Australian fur seals (Arctocephalus pusillus doriferus), New Zealand fur seals (Arctocephalus forsteri), Australian sea lions (Neophoca cinerea) and New Zealand sea lions (Phocarctos hookeri) were targeted for their skins and some oil. At least 1,081 tons of elephant seal oil were shipped from King Is. between 1802 and 1819, while 8,380 tons were shipped from Macquarie Is. between 1810 and 1919. More than 1.4 million skins of both species of fur seals were harvested between 1792 and 1949, but only 4,000 Neophoca and 5,700 Phocarctos pelts are recorded as having been shipped by 1840. The Antipodes Islands yielded more than a quarter of the total fur seal skin harvest, and New Zealand and southern Australia each delivered a quarter of the total. Current numbers of the two species of fur seals combined are about a tenth of the crudely estimated size (1.5 million) of the original population. The exploited fur seals and sea lions were probably the same species as occur today at the original sealing localities, apart from Macquarie Is. where the identity of the exploited fur seals remains in doubt. There is some evidence that Maoris and Australian Aborigines hunted seals in pre-European times, resulting in reduced ranges and depleted stocks that were exploited later by colonial sealers.
Tesi sul tema "Southern fur seals Ecology South Africa"
1
Page, Brad, e page bradley@saugov sa gov au. "Niche partitioning among fur seals". La Trobe University. Zoology Department, School of Life Sciences, 2005. http://www.lib.latrobe.edu.au./thesis/public/adt-LTU20060622.153716.
Testo completoAbstract (sommario):
At Cape Gantheaume, Kangaroo Island (South Australia), adult male, lactating female
and juvenile New Zealand (NZ) and Australian fur seals regularly return to the same
colony, creating the potential for intra- and inter-specific foraging competition in nearby
waters. I hypothesised that these demographic groups would exhibit distinct foraging
strategies, which reduce competition and facilitate their coexistence. I analysed the diet
of adult male, adult female and juvenile NZ fur seals and adult male Australian fur seals
and studied the diving behaviour of adult male and lactating female NZ fur seals and the
at-sea movements of juvenile, adult male and lactating female NZ fur seals. Female diet
reflected that of a generalist predator, influenced by prey availability and their
dependant pups� fasting abilities. In contrast, adult male NZ and Australian fur seals
used larger and more energy-rich prey, most likely because they could more efficiently
access and handle such prey. Juvenile fur seals primarily utilised small lantern fish,
which occur south of the shelf break, in pelagic waters. Juveniles undertook the longest
foraging trips and adult males conducted more lengthy trips than lactating females,
which perform relatively brief trips in order to regularly nurse their pups. Unlike lactating
females, some adult males appeared to rest underwater by performing dives that were
characterised by a period of passive drifting through the water column. The large body
sizes of adult males and lactating females facilitated the use of both benthic and pelagic
habitats, but adult males dived deeper and for longer than lactating females, facilitating
vertical separation of their foraging habitats. Spatial overlap in foraging habitats among
the age/sex groups was minimal, because lactating females typically utilised continental
shelf waters and males used deeper water over the shelf break, beyond female foraging
grounds. Furthermore, juveniles used pelagic waters, up to 1000 km south of the
regions used by lactating females and adult males. The age and sex groups in this
study employed dramatically different strategies to maximise their survival and
reproductive success. Their prey and foraging habitats are likely to be shaped by body
size differences, which determine their different physiological constraints and metabolic
requirements. I suggest that these physiological constraints and the lactation
constraints on females are the primary factors that reduce competition, thereby
facilitating niche partitioning.
2
Stewardson, Carolyn Louise. "Biology and conservation of the Cape (South African) fur seal arctocephalus pusillus pusillus (Pinnipedia: Otariidae)from the Eastern Cape Coast of South Africa /". View thesis entry in Australian Digital Theses Program, 2001. http://thesis.anu.edu.au/public/adt-ANU20030124.162757/index.html.
Testo completo