Dissertations / Theses on the topic 'White shark Marine ecology'

The presence of white sharks Carcharodon carcharias in False Bay, South Africa follows a clear seasonal cycle. In the austral winter months, white sharks aggregate around Seal Island with female sharks in particular moving to the inshore areas in summer. What triggers these fine scale migrations at one of the largest white shark aggregation sites in the world remains a subject of debate. Previous research identified the environmental variables, water temperature and lunar phase, as significant influences on white shark presence inshore. In this study, I attempt to investigate the influence of prey fish availability on the presence of white sharks at two inshore areas of False Bay, namely Muizenberg and Fish Hoek. In addition, I explored the influence of sea surface temperature (SST), El Niño/Southern Oscillation (ENSO), dolphin presence, diatom patch presence and the occurrence of purse-seine fishing (treknetting) on shark presence. A total of 1209 shark sightings were recorded from 1 January 2006 - 31 December 2015 with 742 sightings at Muizenberg and 467 at Fish Hoek. I used randomization tests to determine whether the occurrence of shark sightings was randomly distributed across the environmental and biological variables and determined the dependencies between the predictor variables. I confirmed that shark sightings were clearly seasonal and sightings peaked between 17.49 - 18.57°C. Fish presence revealed a similar peak at 17.94°C. Randomization tests indicate that a spotter is 66% more likely to detect a shark when fish are present, which supports my prediction of a prey mediated cue. The occurrence of treknetting was also found to be non-randomly linked to white shark presence, increasing the probability to spot a shark to 38% instead of 20% at random. The presence of diatom patches was found to be negatively correlated with SST; with numbers increasing in colder waters. The presence of dolphins, as other predators in False Bay, didn't show a significant pattern with any of the analysed variables. The influence of ENSO on the presence of white sharks was also hypothesized and the data revealed that there was a significant influence of weak negative ENSO values on their inshore occurrence. In addition to providing a better understanding of the ecology of white sharks in False Bay, my results can also be used in shark safety and education programs to reduce the risk of shark human conflict.

Includes abstract.<br>Includes bibliographical references.<br>In response to an increase in shark attacks in the Western Cape over the last decade, a shark warning system called Shark Spotters that records white sharks (Carcharodon carcharias) in the surf zone was implemented in 2004 in Cape Town, South Africa.

'White Shark Cage Diving' (WSCD) enables tourists to experience a face-to-face encounter with wild sharks in the open water. In order to attract the animals close to the cages, tour operators often use chum, bait, or decoys, which interferes with the natural habits of marine wildlife. These practices have great potential to adversely impact animals and the marine environment, with unknown long-term consequences. Globally, South Africa has the most extensive WSCD industry. The management is based on a policy paper and regulations published in 2008 by the Minister of Environmental Affairs (a ministry which also included Tourism). This thesis discusses the question of whether South Africa's WSCD industry is appropriately regulated in the light of today's best practices. South Africa's regulatory framework will be compared to the management arrangements of other jurisdiction where WSCD takes place. The ultimate objective of this thesis is to determine whether the South Africa's WSCD regime strikes a sustainable balance between commercial interests and the need to protect this elusive creature.

Chapter 1 The mating systems of two annually-reproducing hammerhead sharks (scalloped hammerhead Sphyrna lewini, bonnethead Sphyrna tiburo) were investigated by genetically-profiling 82 litters (902 embryos). Unlike three biennially-reproducing shark species previously studied that are polygynandrous, genetic monogamy was common in females of both of these hammerheads (S. lewini [70.6 % of litters], S.tiburo [85.4-62.5%]), suggesting a polygynous mating system overall. These mating system characteristics suggest that hammerheads may have lower ratios of effective to census population sizes than polygynandrous sharks, adding to conservation concerns for these species. Results suggest that female mating behavior may play a more limited role in determining the population-level of multiple paternity than currently envisioned in sharks, with the interplay between male mating tactics and female reproductive periodicity (biennial or annual) perhaps being more influential. Two lines of evidence infer that multiple paternity is associated with larger females in S. tiburo: mothers of multi-sired litters are significantly larger than mothers of single paternity litters in West Florida and the frequency of multiple paternity is significantly higher in South Carolina, where females are larger. Large females may therefore produce larger, more genetically-diverse litters in some shark species and could contribute disproportionately to recruitment and population genetic diversity, increasing their importance from a conservation perspective. Chapter 2 Although most shark species have relatively small body-sizes as adults (<100 cm total length), little is known about the genetic population structure and lineage diversification of small sharks. Mitochondrial control region and nuclear internal transcribed spacer 2 sequences combined with three independent microsatellite loci all concordantly show that the diminutive hammerhead shark Sphyrna tiburo (bonnethead) consists of two highly divergent lineages from South Carolina, U.S.A. to Belize, a coastal distance of less than 6000 km. One lineage was restricted to Belize, while the other was almost completely restricted to five North American sampling sites (pairwise CR ΦST = 0.891-0.915, microsatellite Fst=0.277-0.319). This represents the highest degree of population structure recorded concordantly at both mitochondrial and nuclear loci in a shark along a continuous coastline. Regional measures of population structure and genetic divergence in this diminutive hammerhead shark mirror but exceed values obtained for larger shark species over the same sampling range and are comparable to those observed in a larger congener on a global scale. Direct evidence of interbreeding between these lineages indicates that speciation has not yet occurred. Gene-flow was generally high among North American populations, but there was evidence that female-mediated gene flow is moderately restricted between subtropical Florida Bay and higher latitude populations, suggesting that changes in latitude and climate regime may help drive population genetic differentiation in this species. This study is the second to reveal unexpectedly high lineage diversification within Atlantic hammerhead sharks, which suggests that further genetic surveys are required to fully understand and conserve hammerhead shark biodiversity in this region. Chapter 3 Dried fins from the scalloped hammerhead shark (Sphyrna lewini) are highly-valued for utilization in the Asian delicacy shark-fin soup. While global landings of this species annually measure in the millions to supply this market, Western Atlantic populations have collapsed and are now considered to be endangered. This study reveals that Western Atlantic S. lewini comprise at least three distinct management units that will be reliant on intrinsic reproduction rather than immigration for rebuilding (MU’s: U.S.A., Central American Caribbean and Brazil; overall ΦST=0.64). These MU’s are sufficiently differentiated from each other, eastern Atlantic and Indo-Pacific stocks to use mixed-stock analysis (MSA) to better understand the impact of the fin trade on sharks of this region. Stock of origin was determined for 57 Hong Kong market-derived S. lewini dried fins, revealing that contemporary trade is globally-sourced with a substantial presence of fins from imperiled Western Atlantic stocks. Results are used to formulate regional management recommendations and to develop monitoring strategies for the Asian fin trade that could dramatically improve global conservation of S. lewini and serve as a template for other sharks impacted by this trade. Chapter 4 Longline sampling (83 sets) supplemented with 6 pop-off archival tag (PAT) deployments were used to characterize vertical habitat use by Caribbean reef sharks, Carcharhinus perezi, at Glover’s reef atoll, Belize. Longline CPUE in two shallow reef habitats (lagoon < 18m depth, fore-reef < 40 m depth) underwent significant nocturnal increases for sharks larger than 110 cm total length (TL) but not for smaller sharks. Nocturnal CPUE of small sharks increased in the lagoon and decreased on the fore-reef, suggesting movements to avoid larger conspecifics. PAT deployments (7-20 days) indicate that large C. perezi generally increased the amount of time they spent in the upper 40 m of the water column during the night and have a much wider depth and temperature range than previously thought (0 to 356 m, 31-12.4oC). The wide vertical range of this top-predator reveals ecological coupling of deep and shallow reef habitats and has implications for place-based conservation. Chapter 5 Marine Protected Areas (MPAs) are increasingly advocated for the restoration and conservation of coral reef ecosystems, yet given the typically small size of most no-take MPAs it remains unknown how effective this strategy will be for roving, top-level predators such as sharks. Movement patterns of Caribbean reef sharks, Carcharhinus perezi, tagged with coded acoustic transmitters were monitored with an array of up to 22 underwater receivers from May 2004 to October 2006 at Glover’s Reef Marine Reserve, a zoned MPA in Belize. Thirty one tagged sharks ranged in size from 80-215 cm total length [TL], spanning young-of-the-year to mature specimens of both genders. Twenty five of these sharks provided data for more than one week after tagging. Individual sharks were detected within the array on from 5 to 464 days and all but four were predominantly detected on the receiver(s) nearest their original capture. Although daily movements of up to 20-50 km were documented by large sharks (>110 cm TL), most individuals were detected at Glover’s Reef on an almost daily basis throughout the year and appear to be residents of this reef system. Small sharks were documented to be residents for at least six months. The daily dispersal ranges and distribution of sharks tracked in this study suggest that typically small-sized no-take zones will be of limited value for reef shark conservation. However, the long-term residency and site-fidelity of large and small C. perezi to this reef system in its entirety indicates that nesting this no-take zone within a broader ocean zoning plan tailored to protect large roving predators achieves the scale necessary to provide meaningful protection for these ecologically important, threatened predators.

Female mammals play a central role in determination of social structure and are thus central to understanding the overall fission-fusion grouping pattern characteristic of many delphinid societies. Focusing specifically on female-female relatedness and association patterns, I have analysed more than 17 years of group composition, behavioural data, and genetic information to investigate complex interactions between behavioural ecology and relatedness and to also examine the common social evolutionary theory, that variation in mammalian social systems is typically attributed to five main factors: inclusive fitness, predation pressure, sexual conflict and male harassment, inbreeding avoidance, and resource competition. Overall, I found that female bottlenose dolphin association patterns depend upon the interplay between matrilineal kinship, biparental relatedness and home range overlap, and that female bottlenose dolphins seem to adapt their social strategies to seasonal variation in levels of predation and male harassment. The presence of both high sexual conflict and bisexual philopatry lead me to investigate the extent of inbreeding avoidance. I found that more than 14% of the calves were most likely the product of mating between close relatives, and identified female fitness costs to inbreeding. We were able to show that the effect of inbreeding on females??? fitness occurs via two independent mechanisms: being inbred and having at least one inbred calf. Inbred calves are on average weaned later than non-inbred calves, and a female???s first calf has a higher probability to be an inbred than subsequent calves. Last, I examined whether sociality provides inclusive fitness to female bottlenose dolphins through an investigation of both the additive genetic and social variance components of female calving success using a pedigree-free animal model. I found that variance in calving success of female bottlenose dolphins is best explained by complex genetic and social interactions. Females with high calving success showed both high genetic and social merit; they not only have good genes but also prefer to associate with others of high fitness. This study reveals that both social and heritable genetic variance contribute to fitness trait variance in the wild.

The microbiome (microbial community) of individuals is crucial when characterizing and understanding processes that are required for organism function and survival. Microbial organisms, which make up an individual’s microbiome, can be linked to disease or function of the host organism. In humans, individuals differ substantially in their microbiome compositions in various areas of the body. The cause of much of the composition diversity is yet unexplained, however, it is speculated that habitat, diet, and early exposure to microbes could be altering the microbiomes of individuals (Human Microbiome Project Consortium, 2012b, 2012a). To date, only one study has reported on microbiome characterization in a shark (Doane et al., 2017; skin microbiome of the common thresher shark). A comparative characterization of microbiomes sampled from different shark species and anatomical locations will allow an understanding of the differences in microbiomes that may be explained by variance in shark habitat and diet. Florida leads as shark bite capitol of the world, with 778 unprovoked bites recorded since 1837, or 4-5 average bites per year. With only a few bites a year, there is not a lot of opportunities to study these bites. What can be studied, however, is how the microbial environment in shark’s teeth is composed. To understand overall microbiome composition, and if microbiomes are distinct from the environment, or specific by species or anatomical location (henceforth location), we characterized microbiomes from the teeth, gill, skin, and cloacal microbiomes of 8 shark species in south Florida (nurse, lemon, sandbar, Caribbean reef, Atlantic sharpnose, blacktip, bull, and tiger) using high throughput DNA sequencing of the 16S rRNA gene V4 region. There was a significant difference in microbial community richness among species, sample location, but not the interaction between species and location. Microbial diversity by location was significantly different for both the Shannon index and Inverse Simpson index. Samples examined by species had no significant difference in microbial community diversity overall for both Shannon and Inverse Simpson indexes. Microbial community diversity of samples by location and species combined significantly differed when submitted to an analysis of variance with the Shannon index, but not the Inverse Simpson index. Teeth microbial communities showed the most diversity based on both Shannon and Inverse Simpson indices. Teeth microbiomes are distinct but also share taxa with the water they inhabit, including potentially pathogenic genera such as Streptococcus (8.0% ± 9.0%) and Haemophilus (2.9% ± 3.3%) in the Caribbean reef shark. The lemon shark teeth hosted Vibrio (10.8% ± 26.0%) and the Corynebacterium genus (1.6%±5.1%). The Vibrio genus (2.8% ± 6.34%), Salmonella enterica (2.6% ± 6.4%), and the genus Kordia (3.1% ± 6.0%) are found in the nurse shark teeth microbial community. Strikingly, the Vibrio genus was represented in the sandbar shark (54.0% ± 46.0%) and tiger shark (5.8% ±12.3%) teeth microbiomes. One OTU related to traditionally non-pathogenic family Phyllobacteriaceae appear to be driving up to 32% of variance in teeth microbiome diversity. We conclude that south Florida sharks host distinct microbiomes from the surrounding environment and vary among species due to differences in microbial community richness. Future work should focus on bacteria found in shark teeth to determine if those present are pathogenic and could provide insights to bite treatment.

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.<br>Dissertation (MSc)--University of Pretoria, 2012.<br>Zoology and Entomology<br>MSc<br>Unrestricted

Nearshore marine environments are known to be highly productive systems with relatively high faunal diversity and abundances, but these systems are particularly vulnerable to negative impacts from anthropogenic disturbances that can result in habitat degradation. Despite these challenges, many shark species of various life stages utilize coastal shelf habitats, inshore estuaries, and bays. The inshore habitats of Cumberland and Nassau Sounds in northeast Florida have been proposed as potential nursery grounds by earlier work, but this suggestion did not satisfy all of the standard criteria of shark nursery designation. It has recently been stated that the combination of surveys inside and outside suspected nursery habitats, especially those incorporating mark-recapture studies, would provide a very comprehensive test of the nursery criteria. A primary objective of the present study was to initially describe the composition and abundance of shark populations utilizing the nearshore habitats of northeast Florida, while also comparing them to inshore communities, with emphasis on spatial and temporal variations in assemblages. Fishery-independent longline sampling was conducted across the region and while considerable overlap of species were observed, significant differences in community structure between inshore and nearshore locations were detected. Specifically, the inshore waters of the First Coast support nursery habitat designation for Atlantic sharpnose, blacktip, and sandbar sharks after satisfying the accepted criteria. Given the high amounts of spatial and temporal overlap observed along the First Coast, relative trophic niche dynamics were also investigated via stable isotope analysis of two tissue types. These results revealed varying trophic niche sizes in the long term, but suggest some degree of shared resource use when animals are present on the First Coast. The identification of factors that influence coastal shark habitat utilization, such as competition and resource use, can contribute to understanding and predicting how they may respond to future environmental changes.

Thesis (M.S.)--George Mason University, 2008.<br>Vita: p. 103. Thesis director: Robert B. Jonas. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Science and Policy. Title from PDF t.p. (viewed July 3, 2008). Includes bibliographical references (p. 96-102). Also issued in print.

As climate change continues, climactic extremes are predicted to become more frequent and intense, in some cases resulting in dramatic changes to ecosystems. The effects of climate change on ecosystems will be mediated, in part, by biotic interactions in those ecosystems. However, there is still considerable uncertainty about where and how such biotic interactions will be important in the context of ecosystem disturbance and climactic extremes. Here, I review the role of consumers in seagrass ecosystems and investigate the ecological impacts of an extreme climactic event (marine heat wave) and subsequent widespread seagrass die-off in Shark Bay, Western Australia. Specifically, I compare seagrass cover, shark catch rates, and encounter rates of air breathing fauna in multiple habitat types before and after the seagrass die-off to describe post-disturbance dynamics of the seagrass community, shifts in consumer abundances, and changes in risk-sensitive habitat use patterns by a variety of mesoconsumers at risk of predation from tiger sharks (Galeocerdo cuvier). Finally, I conducted a 16 month field experiment to assess whether xi loss of top predators, and predicted shifts in dugong foraging, could destabilize remaining seagrass. I found that the previously dominant temperate seagrass Amphibolis antarctica is stable, but not increasing. Conversely, an early-successional tropical seagrass, Halodule uninervis, is expanding. Following the die-off, the densities of several consumer species (cormorants, green turtles, sea snakes, and dugongs) declined, while others (Indo-Pacific bottlenose dolphins, loggerhead sea turtles, tiger sharks) remained stable. Stable tiger shark abundances following the seagrass die-off suggest that the seascape of fear remains intact in this system. However, several consumers (dolphins, cormorants) began to use dangerous but profitable seagrass banks more often following seagrass decline, suggesting a relaxation of anti-predator behavior. Experimental results suggest that a loss of tiger sharks would result in a behaviorally mediated trophic cascade (BMTC) in degraded seagrass beds, further destabilizing them and potentially resulting in a phase shift. My work shows that climactic extremes can have strong but variable impacts on ecosystems mediated in part by species identity, and that maintenance of top predator populations may by important to ecological resilience in the face of climate change.

Recent research suggests that brackish, marine-derived groundwater up-wells in the oligohaline ecotone of the coastal Everglades, bringing with it phosphorus to an otherwise phosphorus-poor environment. The purpose of this study is to estimate the rates and timing of the groundwater discharge by using variable-density groundwater models constructed, calibrated, and validated with field measurements of hydraulic head and surface and subsurface temperature. Modeled groundwater discharge rates ranged from 5.4E-04 mm/day in August to -1.3E-03 mm/day in June for Shark Slough and 4.8E-01 mm/day in June to -1.4E-01 mm/day in January for Taylor Slough, where positive values imply groundwater discharge and negative values imply groundwater recharge. These results indicate that groundwater discharge rates during the period of study were low and perhaps a negligible source of marine-derived phosphorous in the oligohaline ecotone of Shark Slough but much higher and perhaps significant source of marine-derived phosphorous in the oligohaline ecotone of Taylor Slough.

Coral diseases were first noted in the 1960s and 1970s and have had major impacts globally on coral reef community structures. In the Caribbean, a major outbreak of white band disease has been considered responsible for the drastic decline of Caribbean Acroporids since the 1970s. In addition to white band disease, another more recently described condition known as rapid tissue loss (RTL) has had major impacts on Acropora cervicornis populations, specifically offshore Broward County Southeast Florida. While these diseases have contributed to the population decline, determining their etiologies has been elusive. Coral diseases have been characterized by shifts in their microbial counterparts within many levels of the coral host. While some coral diseases have had specific pathogens identified, research has not been able to determine pathogens for most. Evidence points toward bacterial causes for many diseases, but due to the complexity of the coral holobiont and the interaction with the environment, elucidating the causes has proven difficult. Many studies have examined the microbiomes of specific diseases and determined some potential pathogens or at least taxa playing important roles in the disease, although none have looked at RTL. Recognizing the local affect of RTL on A. cervicornis, this study set out to gain a baseline understanding of the healthy and RTL affected microbiome of A. cervicornis. 16S rRNA gene sequencing was used to examine the microbiome of completely healthy colonies, healthy regions of diseased colonies, and the disease margin of diseased colonies. Analysis of four microbial diversity metrics revealed marked increases in diversity with respect to declining health states. Additionally, community dissimilarity analysis and analysis of differentially abundant taxa exhibited distinct microbial community structures due to coral health. Several highly abundant (Rickettsiales, Rhodobacteraceae) and a few low abundance (Bdellovibrionales) taxa were identified as primary drivers of the differences. Additionally, Piscirickettsiaceae, a known fish pathogen, was consistently associated with RTL and warrants further investigation. All of the taxa identified with in RTL have been associated with other Acroporid and non-Acroporid diseases throughout the Caribbean and the rest of the world. The consistent IV association of similar taxa for coral diseases around the world, including those found in this study, supports the recent ideas of non-specific primary pathogens. While most disease studies, coral and otherwise, aim to determine a single pathogen for a single disease, this study and others suggest there could be a multitude of organisms responsible for the disease. Therefore understanding the interactions of the coral holobiont and the environment is important to understanding coral disease. While this study reveals significant changes in the bacterial community associated with RTL as well as some potential pathogens, the relationships appear complex and perhaps at a functional level rather than merely taxonomic. Furthermore, this study did not examine viruses, fungi, or protists, which could be possible pathogens. Therefore, to further develop an understanding of RTL and many other coral diseases it will be necessary to consider additional none-bacterial members of the holobiont as well as the bacterial functions and taxa coupled with the roles of environmental factors.

The aim of this study was to investigate various aspects of the life history of white sharks Carcharodon carcharias at Dyer Island, South Africa, between August 1999 and January 2001. Inter-specific predatory interactions between the white shark and various potential prey species such as the Cape fur seal (Arctocephalus pusillus pusillus), African penguin (Spheniscus demersus), Cape cormorant (Phalacrocorax capensis), bank cormorant (P. neglectus), crown cormorant (P. coronatus) and white-breasted cormorant. (P. carbo) were observed. White sharks were attracted daily to a research vessel positioned at various anchorages in the vicinity of Dyer Island. Spatial and temporal abundance, and population composition of white sharks were recorded throughout the year and revealed seasonal trends in habitat utilisation. White sharks occupied inshore waters, away from the Geyser Rock seal colony in the summer. Sharks became abundant in the near vicinity of Geyser Rock in the winter period. The summer inshore population was characterised by the increased total length of sharks and the exclusive presence of female sharks. Prey resembling decoys were used to investigate trends in the 'predatory motivation' of white sharks in relation to various independent variables. White sharks displayed greatest predatory motivation in close proximity to a seal colony, in overcast conditions, and when water clarity was low. White sharks evidently elevate their motivation to hunt large prey, which are difficult to catch, in situations where the likelihood of encountering valued prey and completing a successful attack is greatest. Ontogenetic difference in predatory motivation towards the decoys existed, with sharks above 325 cm TL displaying greater predatory motivation than smaller sharks. Various choice tests were conducted to determine the visual discriminatory ability and prey preference of white sharks at Dyer Island. The results suggested that white sharks preferred a biologically familiar shape (pinniped) over an inanimate shape (rectangle), smaller (75 mm TL pinniped) over larger (1800 mm TL pinniped) prey, and a pinniped decoy over a penguin decoy of similar size. Selectivity in larger white sharks (>375 cm TL) was most noticeable in the prey shape (pinniped vs. rectangle) experiment, which suggests they may readily utilise a speculative hunting strategy based on rough similarities between detected potential prey and recognised prey. In this situation mistaken identification of prey is more possible. Smaller white sharks (a majority of the sample) displayed most selectivity in the prey size experiment, with strong preference for the smaller seal decoy over the large one. This pattern indicates that prey size may be a partial limiting factor in the feeding of smaller white sharks. Negative impacts (such as conditioning or distraction) of cage-diving on white sharks were assessed by the measurement of white shark contact time and visit time in relation to the chumming vessel. These results revealed that smaller sharks had longest visit times, and that sharks in the vicinity of Geyser Rock displayed visitation patterns indicative of hunting sharks. Particular vigilance should be kept by operators not to allow small sharks to take bait (reward). The channel area appears to be an important hunting ground and white shark cage-diving should perhaps be restricted in this area. White sharks also showed greater activity around the chumming vessel on cloudy days and operators must be particularly vigilant to deny sharks any rewards (bait) under these conditions. Both the white sharks and Cape fur seals predate and/or attack seabirds and predatory interactions were quantified and qualified by the routine collection and inspection of seabird carcasses and injured birds, as well as opportunistic observations of live attacks throughout this study. White sharks are infrequent predators of seabirds in this ecosystem, perhaps due to an abundance of Cape fur seals (a preferred prey), anti¬predator behaviour by penguins, and seabirds not being a sought after prey type. Cape fur seals were a more conspicuous seabird predator, annually attacking a significant percentage of the adult penguin (1.99-2.52%), white-breasted cormorant (5.21-5.72%), and crowned cormorant (3.13%) populations. A minimum estimate of 1.09% of the fledgling Cape cormorant population also succumbed to Cape fur seal predation.<br>Dissertation (MSc(Zoology))--University of Pretoria, 2006.<br>Zoology and Entomology<br>unrestricted