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Foraging ecology of white sharks Carcharodon carcharias at Dyer Island, South AfricaJewell, Oliver Joseph David 20 June 2013 (has links)
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. / Dissertation (MSc)--University of Pretoria, 2012. / Zoology and Entomology / MSc / Unrestricted
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Biology and conservation of the Cape (South African) fur seal Arctocephalus pusillus pusillus (Pinnipedia: Otariidae) from the Eastern Cape Coast of South AfricaStewardson, Carolyn Louise, carolyn.stewardson@anu.edu.au January 2002 (has links)
[For the Abstract, please see the PDF files below, namely "front.pdf"] CONTENTS. Chapter 1 Introduction. Chapter 2 Gross and microscopic visceral anatomy of the male Cape fur seal with reference to organ size and growth. Chapter 3 Age determination and growth in the male Cape fur seal: part one, external body. Chapter 4 Age determination and growth in the male Cape fur seal: part two, skull. Chapter 5 Age determination and growth in the male Cape fur seal: part three, baculum. Chapter 6 Suture age as an indicator of physiological age in the male Cape fur seal. Chapter 7 Sexual dimorphism in the adult Cape fur seal: standard body length and skull morphology. Chapter 8 Reproduction in the male Cape fur seal: age at puberty and annual cycle of the testis. Chapter 9 Diet and foraging behaviour of the Cape fur seal. Chapter 10(a) The Impact of the fur seal industry on the distribution and abundance of Cape fur seals. Chapter 10(b) South African Airforce wildlife rescue: Cape fur seal pups washed from Black Rocks, Algoa Bay, during heavy seas, December 1976. Chapter 11(a) Operational interactions between Cape fur seals and fisheries: part one, trawl fishing. Chapter 11(b) Operational interactions between Cape fur seals and fisheries: part two, squid jigging and line fishing. Chapter 11(c) Operational interactions between Cape fur seals and fisheries: part three, entanglement in man-made debris. Chapter 12 Concentrations of heavy metals (Cd, Cu, Pb, Ni & Zn) and organochlorine contaminants (PCBs, DDT, DDE & DDD) in the blubber of Cape fur seals. Chapter 13 Endoparasites of the Cape fur seal. Chapter 14(a) Preliminary investigations of shark predation on Cape fur seals. Chapter 14(b) Aggressive behaviour of an adult male Cape fur seal towards a great white shark Carcharodon carcharias. Chapter 15 Conclusions and future directions.
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