1,721,121 research outputs found
Reactions of Heaviside's dolphins to tagging attempts using remotely-deployed suction-cup tags
Get PDFTagging attempts of Heaviside's dolphins (Cephalo-rhynchus heavisidii) using a remotely-deployed suction-cup tag were performed in Table Bay and St Helena Bay on the southwest coast of South Africa. The observed reactions of dolphins indicate that this tagging approach has negligible impacts on the dolphin behaviour and Heaviside's dolphins might be tagged with suction cup tags without adverse affects.link_to_subscribed_fulltex
Habitat selection, seasonal population changes, and behaviour of the Amsterdam Island fur seal Arctocephalus tropicalis on Gough Island
Get PDFThesis (DSc (Zoology))--University of Pretoria, 1977.The population size and seasonal cycle of the Amsterdam Island fur seal ( A. tropicalis) at Gough Island ( 40°20'S, 9°54'W) were investigated in the summers of 1974/75 and 1975/76. Population size was determined by direct census of part of the coast, and by comparison with a reliable total census made in the summer of 1955/56. Correction factors for undercounting and seasonal cycle were applied. Population size is approximately 100 000 and is the largest known population of this species. Seasonal cycle for various age and sex groups was determined by regular counting at four study beaches. A definite summer breeding peak and an autumn moulting peak exist in A. tropicalis at Gough Island. The peak in numbers ashore during the moult is an hitherto undescribed feature of the seasonal cycle of the Arctocephalinae. Mainly nonbreeding seal colonies occur on the east coast while the breeding colonies are situated on the west coast. Their location is determined by topographical, oceanographic and climatological factors. The diurnal haulout and activity patterns of A. tropicalis are described and environmental factors that modify it are discussed. High local ambient temperatures and solar radiation during the summer have a definite influence on the fur seals. Behavioural and postural adjustments are made use of to supplement physiological means of thennoregulation. Postures and vocalizations as a means of communication in inter- and intrasexual encounters were investigated, and territorial male behaviour studied during the breeding season. Adult males show a seasonal change in territoriality and five territory types are distinguished, based on their location on the beach, time of formation, duration of maintenance, size, topographical definition, and their success in attracting females. Interactions between territorial males involve little physical contact, with boundary displays to affirm territory boundaries and advertise territorial status, being more common. Fighting technique and boundary displays are described, as well as adult male involvement with adult females. The latter is mainly directed at the containment of females on a territory, assessment of their reproductive state and possibly also has a communicative value. Females' reactions towards the attention of adult males usually have elements of submission. Mother-pup relations were investigated and an account is given of general intra- and interspecific behaviour.Zoology and EntomologyDSc (Zoology)Unrestricte
A clinical assessment of the morphometrics of African elephant tusks
Get PDFDissertation (MSc)--University of Pretoria, 2008.No abstract available.Zoology and Entomologyunrestricte
The diving and ranging behaviour of southern elephant seal, Mirounga leonina, bulls
Get PDFDissertation (MSc (Zoology))--University of Pretoria, 1998.Geolocation-Time-depth Recorders (GLTDRs) were used to record the diving and ranging behaviour of eleven southern elephant seal, Mirounga leonina, adult males from sub-Antarctic Marion ( n = 7) and Macquarie ( n = 4) Islands during their pelagic annual cycle. A total of 39 897 dives during 894 days were recorded and were categorised into twelve dive types which were hypothesized to serve in travelling, searching for prey, exploration, resting, benthic foraging, pelagic foraging and combinations of two or more functions, and seals dived virtually continuously (86%-92% of the time underwater) most often to depths ranging from 390 m to 920 m and dive durations from 18.6 min to 36.6 min (maximum duration= 80 min) spending only 2.4 min to 3.6 min on the surface between dives. Although the maximum measured dive depths for two males from Marion Island (1 446 m and I 452 m) are the deepest dives measured yet for male southern elephant seals, these seals often exceeded the depth limit of the GLTDRs. The Macquarie males travelled to Antarctica mostly foraging benthically over the Antarctic continental shelf whilst the males from Marion Island stayed relatively close to the island, diving deeper and longer pursuing pelagic prey species. The results in this study suggest that different physical environmental conditions resulted in the different diving behaviours displayed by M leonina males. 11Zoology and EntomologyMSc (Zoology)Unrestricte
Life history parameters and regulation of the southern elephant seal population at Marion Island
No full textThesis (PhD (Zoology))--University of Pretoria, 2006.Pup mortality of southern elephant seals at Marion Island from 1990 through 1999 ranged from 1.6 to 7.3%, averaging 3.8%. Pup mortality was density independent and dismissed as being a major population regulating agent at Marion Island. Juvenile survival over two periods, one during the population decline and the other after the population had stabilised, was assessed and compared using mark-recapture models. Survival was age- but not sex-related and on average, the probability of survival was 59.5%,81.4% and 78.1% for the first, second and third year respectively. There was no significant difference in survival over the two periods and juvenile survival does not appear to be an important population regulating component in the southern elephant seal population. Mark-recapture data for females from the Marion Island population since the population stabilisation (1994) was analysed and compared with similar data collected during the decline and with data collected from the increasing population in southern Argentina. Survival of prime-age adult females increased by 8% concurrent with the stabilisation at Marion Island, which ultimately compensated for an annual rate of decline of the population of 5.85% until 1994. Survival of adult females at the colony in southern Argentina was 6% greater than at Marion Island after the stabilisation. Adult female survival is concluded to predominantly regulate the population. Changes in adult female survival and breeding probabilities with age were quantified in order to measure the prevalence of senescence in the population. Less than a 1 % difference between prime-age and post prime-age survival was found over eight cohorts of marked females and no evidence of reproductive senescence in terms of reduced breeding probability with age was detected. Five percent of southern elephant seal females survived to age ten and 0.5 % to the age of seventeen. Pubescent male survival increased concordant with the population stabilisation. These animals have high energetic demands due to a secondary growth spurt during which growth is accelerated and this increase lends support to the hypothesis that food has been limiting the population at Marion Island. Future survival and breeding probabilities of females primiparous at different ages were estimated in order to investigate potential future fitness costs associated with early breeding. Annual future survival of females breeding at age three was the same as that for females primiparous at four and slightly higher than that for females primiparous at five and six. Future breeding probabilities of females primiparous at three were similar to that for females primiparous at four and older. I found no evidence for future fitness costs incurred through reproductive expenditure and conclude that age of primiparity IS determined by acquisition of a critical body mass, after which no future delay in reproduction takes place. I estimated future survival and capture probabilities of southern elephant seals that winter at Marion Island during their first three years and compared these values to similar estimates from individuals that were not observed to winter over the same time periods. There were no significant differences in survival between wintering and non-wintering elephant seals suggesting that survival is not a fitness correlate of wintering behaviour. I provide unique evidence of differential site fidelity within age- and sex classes, which has implications for population modelling.Zoology and Entomologyunrestricte
Predatory interactions between Cape fur seals and seabirds at Ichaboe Island, Namiba
Get PDFDissertation (MSc (Zoology))--University of Pretoria, 2005.Please read the abstract in the section 00front of this documentZoology and Entomologyunrestricte
The diet of the Subantarctic fur seal Arctocephalus tropicalis at Marion Island
Get PDFDissertation (MSc)--University of Pretoria, 2010.Faecal analysis (n = 806 scats) was employed to examine the diet of the Subantarctic fur seal Arctocephalus tropicalis at Marion Island (46° 54’S, 37° 45’E) over a period of six years (April 2000 – March 2006). Identifiable prey remains (fish otoliths, cephalopod beaks) were extracted from the faeces and analyzed. The number of individuals of each prey group identified was determined, and the size of individuals was estimated by applying appropriate regression formulae to measurements of the prey remains. Despite the biases associated with the method, useful information was gained on seasonal and inter-annual fluctuation in the presence of prey species in the diet. The indices used to investigate these variations were percentage numerical abundance, percentage frequency of occurrence and reconstituted body size (mass and length) of prey species taken. The diet was diverse and myctophid species predominated. Cephalopods were minor prey species in scats (n = 39). The five main prey species were Gymnoscopelus bolini, G. piabilis, G. fraseri, G. nicholsi and Protomyctophum tenisoni. In all respects G. bolini predominated throughout the study period, although in most comparisons no statistically significant differences in the relative contribution amongst the main prey species in the diet were found. Seasonal and inter-annual variations in the contributions of these species to the diet presumably resulted from changes in the relative abundance and distribution of prey.Zoology and EntomologyUnrestricte
The effects of artificial control on the feral cat Felis catus Linnaeus population on Marion Island
Get PDFDissertation (MSc (Zoology))--University of Pretoria, 1991Hunting was used as one method in a long-term campaign to eradicate feral cats on sub-Antarctic Marion Island. A total of 872 cats were shot during 14 725 man-hours over four years. Accurate estimation of cat numbers was not possible, but cats sighted per hour of night hunting was a reliable index of density. Hunting resulted in a marked decrease in density, but became ineffective at low densities and gin trapping was incorporated into the programme. Eighty cats were trapped. Fecundity decreased with the decrease in cat density. Birds decreased significantly in the diet of cats, ascribed to decreased availability as a result of cat predation. Chicks formed a substantial proportion of birds taken. Breeding success of two burrowing petrel species increased with the decrease in cat numbers. Hunting successfully removed large numbers of cats and recovery of bird populations appears likely. The prospects of eradicating the cats are good.ZoologyMSc (Zoology
A demographic comparison of two elephant seal populations
No full textThesis (PhD (Zoology))--University of Pretoria, 2005.The demography of two elephant seal populations was examined and compared. This was done to investigate the reasons for the observed decreases in populations at Marion and Macquarie islands. While a well-established demographic programme had been in place at Marion Island since the 1980's (see Pistorius et al. (l999a) for a review) one had to be established at Macquarie Island. A long-term demographic programme was initiated at Macquarie Island in 1993 and hot brands were used to mark seals. Hot-iron branding was a rapid and reliable method of permanently identifying elephant seals that did not prejudice survival and did not appear to cause undue stress (in the short-term). Neither branding nor handling showed any long-term effects as measured by survival after one year. From the inter-island comparison of survivorship, age at first breeding and wean mass I concluded that the observed decreases in elephant seal numbers between the I 950s and 1990s in the Pacific and Indian Ocean sectors were driven by resource limitation in the Southern Ocean. A conglomerate of factors including local predation by killer whales and intra-specific resource competition was postulated as a cause for the inter-island (regional) differences in population trends. Presently it appears that per capita more resources are available to the Marion Island population than are available to the Macquarie Island population. The vital rates that had the greatest impact (elasticity) on fitness (population growth) for all populations i.e. Marion Island, Macquarie Island and South Georgia, were, in order of importance: (I) juvenile survival, (2) adult survival, (3) adult fecundity and (4) juvenile fecundity. At Marion Island juvenile and adult survival contributed equally to the fitness of the population while at Macquarie Island and at South Georgia Island juvenile survival was more important than adult survival in determining population fitness. The global population of elephant seals in 200 I was estimated at approximately 738 772 which represents an increase of I I % from the last world estimate (664 000). It seems clear from the evidence presented and reviewed here that the present changes in seal populations, unlike the period of direct exploitation in the 19th and 20th centuries, are neither a consequence of direct human interactions nor present-day commercial activities. While the significance of inter-specific competition between elephant seals and other Antarctic predators remain largely unknown or quantified, it would seem prudent that these relationships be studied. This is because resource competitors (toothed whales) have been increasing in number since the cessation of commercial whaling. Even though elephant seals are considered the most studied of all pinnipeds (Ling&Bryden, 1992) much remains to be learnt. Foremost are to gain a clear understanding of the in situ, diet of elephant seals and to assess the role pathogens play in the regulation of seal populations. In addition to these studies it is also important that the current long-term monitoring programmes at Marion and Macquarie islands continue, as they provide valuable base line information on the fate of elephant seal populations.Zoology and Entomologyunrestricte
Foraging ecology of white sharks Carcharodon carcharias at Dyer Island, South Africa
Get PDFDissertation (MSc)--University of Pretoria, 2012.Dyer Island is thought to host one of the most abundant populations of
white sharks on the planet; this is often credited to the large (55 – 60,000) Cape fur
seal colony at Geyser Rock. Yet relatively little work has ever been produced from
the area. This may be attributed to the harshness in its location as a study site, exposed
to wind and swell from west to east which limits research periods. This study
accounts for over 220 hrs of manual tracking at Dyer Island with a further 68 added
from the inshore shallow areas of the bay. Sharks focused their movements and
habitat use to reefs or channels that allowed access to Cape fur seals. Movement-
Based Kernel Estimates (MKDE) were used to compute home range estimates for
shark movements through and around the heterogeneous structures of Dyer Island and
Geyser Rock. Inshore two core areas were revealed, one being the major reef system
at Joubertsdam and the other at a kelp reef where the tracked shark had fed on a Cape
fur seal. At Dyer Island one core area was identified in a narrow channel, ‘Shark
Alley’, here a second tracked shark foraged for entire days within meters of rafting
Cape fur seals.
Rate of Movement (ROM) and Linearity (LI) of tracks were low during daytime and
movements were focused around areas such as Shark Alley or other areas close to the
seal colony before moving into deeper water or distant reefs with higher rates of ROM
and LI at night. If moonlight was strong foraging would take place to the south of
Geyser Rock but with higher ROM and LI than observed during the day. Foraging
patterns in this study contrast studies from other sites in South Africa and home range
and activity areas were comparatively much smaller than observed in Mossel Bay. It has been established that several known white sharks forage at Dyer Island and the
other studied aggregation sites, such differences in foraging would suggest that they
are able to adapt their foraging behaviour to suit the environment they are in; making
them site specific in their foraging ecology.
Both satellite and acoustic telemetry are revealing aggregation hotspots of white
sharks in South Africa. It is important that such information is used to assist the
recovery of the species which has been protected since 1991, yet is rarely considered
in planning of coastal developments.Zoology and EntomologyMScUnrestricte
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