We present 15 individual cases of sub-adult white sharks that were SPOT tagged in South Africa from 2003–2004 and have been re-sighted as recently as 2011. Our observations suggest SPOT tags can cause permanent cosmetic and structural damage to white shark dorsal fins depending on the duration of tag attachment. SPOT tags that detached within 12–24 months did not cause long term damage to the dorsal fin other than pigmentation scarring. Within 12 months of deployment, tag fouling can occur. After 24 months of deployment permanent damage to the dorsal fin occurred. A shark survived this prolonged attachment and there seems little compromise on the animal’s long term survival and resultant body growth. This is the first investigation detailing the long term effects of SPOT deployment on the dorsal fin of white sharks.
Blue Wilderness Research Unit
Blue Wilderness owner – Ryan Johnson is one of South Africa’s most renowned shark biologists. The Blue Wilderness Research Unit drives many of South Africa’s most ambitious and established shark research programs. The Blue Wilderness expedition team collects daily citizen science data that is fed to the research units databases.
We capture ID photos to analyse population dynamics and residency periods of sharks
We collect daily environmental parameters to correlate with shark abundance and behaviour.
We conduct daily census of biodiversity sightings of sharks, fishes and other ocean fauna on Aliwal Shoal.
The Blue Wilderness Research Unit provides and facilitates innovative and dynamic research relevant to the management and conservation of Southern Africa’s wildlife. Students and enthusiasts can contribute to our research efforts though our volunteer program
The work of Ryan Johnson and the researchers of the Blue Wilderness Resarch Unit (BWRU) has made significant contributions to the understanding of sharks and marine predators in South Africa. Presented is some of the recent publications by the scientists of the BWRU
(2016) How solitary are white sharks: social interactions or just spatial proximity?
Findlay, Gennari, Cantor, Tittensor (2016)
White sharks (Carcharodon carcharias) are circumglobally distributed large apex predators. While ecologically important, there is very limited study of their social behaviour. Although evident in other large, apex marine predators (e.g. toothed whales) and smaller elasmobranchs (e.g. blacktip reef sharks), the ability of any large pelagic elasmobranch to demonstrate social preferences, tolerance or grouping behaviour is largely unknown. Here, we test whether white sharks in a near-coastal environment form non-random associations with other conspecifics or simply share the same space at the same time. We photo-identified 323 individuals—74 % juvenile females (175–300 cm)—during chumming events at six different sites in Mossel Bay, South Africa, over a 6-year period (2008–2013), and tested for grouping behaviour. We found evidence for random associations among individuals, though spatio-temporal co-occurrence of white sharks in close proximity was weakly structured according to sex and, potentially, body size. Such biological traits may play a minor part in structuring co-occurrence of individuals at fine spatio-temporal scales, which could reflect ontogenetic preferences in diet and site fidelity, or differing tolerance levels for conspecifics of different sexes and sizes. Our study strengthens the evidence that large pelagic shark species are generally solitary and display limited social behaviour.
(2016) How Close is too Close? The Effect of a Non-Lethal Electric Shark Deterrent on White Shark Behaviour
Kempster , Egeberg , Hart, Ryan, Chapuis, Kerr, Schmidt, Huveneers, Gennari, Yopak, Meeuwig, Collin (2016)
Sharks play a vital role in the health of marine ecosystems, but the potential threat that sharks pose to humans is a reminder of our vulnerability when entering the ocean. Personal shark deterrents are being marketed as the solution to mitigate the threat that sharks pose. However, the effectiveness claims of many personal deterrents are based on our knowledge of shark sensory biology rather than robust testing of the devices themselves, as most have not been subjected to independent scientific studies. Therefore, there is a clear need for thorough testing of commercially available shark deterrents to provide the public with recommendations of their effectiveness. Using a modified stereo-camera system, we quantified behavioural interactions between white sharks (Carcharodon carcharias) and a baited target in the presence of a commercially available, personal electric shark deterrent (Shark Shield Freedom7™). The stereo-camera system enabled an accurate assessment of the behavioural responses of C. carcharias when encountering a non-lethal electric field many times stronger than what they would naturally experience. Upon their first observed encounter, all C. carcharias were repelled at a mean (± std. error) proximity of 131 (± 10.3) cm, which corresponded to a mean voltage gradient of 9.7 (± 0.9) V/m. With each subsequent encounter, their proximity decreased by an average of 11.6 cm, which corresponded to an increase in tolerance to the electric field by an average of 2.6 (± 0.5) V/m per encounter. Despite the increase in tolerance, sharks continued to be deterred from interacting for the duration of each trial when in the presence of an active Shark Shield™. Furthermore, the findings provide no support to the theory that electric deterrents attract sharks. The results of this study provide quantitative evidence of the effectiveness of a non-lethal electric shark deterrent, its influence on the behaviour of C. carcharias, and an accurate method for testing other shark deterrent technologies.
(2015) Abundance and degree of residency of humpback dolphins Sousa plumbea in Mossel Bay, South Africa
James, Bester, Penry, Gennari, Elwen (2015)
Indian Ocean humpback dolphins Sousa plumbea inhabit nearshore waters from South Africa to eastern India. Humpback dolphins are vulnerable to conservation threats due to their naturally small population sizes and use of nearshore habitats, where human activities are highest. We investigated the abundance and residency of this species inhabiting Mossel Bay, South Africa, using photographic mark-recapture. Data were collected during 81 surveys in Mossel Bay between 2011 and 2013. Open population modelling using the POPAN parameterisation produced a ‘super-population’ estimate of 125 individuals (95% CI: 61–260) and within-year estimates of between 33 and 86 individuals (2011: 71 [95% CI: 30–168]; 2012: 33 [15–73], 32 [15–70]; 2013: 46 [20–108]). Although less appropriate, closed capture models were also run for comparison with previous studies in the region and generated similar, but slightly smaller, population estimates within each year. We compared our catalogue with opportunistic data collected from East London, Plettenberg Bay, De Hoop and Gansbaai. The only catalogue matches attained were between Plettenberg Bay (n = 44 identified) and Mossel Bay (n = 67 identified), separated by 140 km. Population exchange was moderate, with nine individuals resighted in multiple years between these two areas. This study supports previous findings of long-range movements for this species and provides a baseline from which to assess future impacts on the population.
(2014) Spatial and seasonal patterns in sighting rate and life-history composition of the white shark Carcharodon carcharias at Mossel Bay, South Africa
Ryklief, Pistorius, Johnson (2014)
White sharks Carcharodon carcharias aggregate at specific times of the year at localities along the South African coast. At Mossel Bay, on the southern Cape coast, four sites were sampled (Seal Island, Hartenbos, Kleinbrak and Grootbrak) to investigate spatial and seasonal patterns in relative abundance and life-history composition. These are known aggregation sites within the bay, each having particular physical and/or biological characteristics. Sightings-per-unit-effort data were collected from February to December 2008–2010. Sighting rates demonstrated significant seasonal and interannual variation at the four sites. The highest mean sighting rate was recorded at Seal Island and the lowest at Hartenbos, which might be a consequence of differences in prey availability. The greatest interannual variability was recorded at Kleinbrak, followed by Seal Island, with little variability at Grootbrak and Hartenbos. White sharks appeared to concentrate at Grootbrak and Kleinbrak in summer and autumn, at Seal Island in winter, and at Hartenbos and Seal Island in spring. All life-history stages were present year-round but their occurrence was influenced significantly by season (p < 0.05), although not site. Few adults (325–424 cm total length) were seen, with the highest frequency being in spring, whereas that of young-of-the-year (≤174 cm) was in autumn. Juveniles (175–324 cm) constituted 78% of the animals sighted, indicating that Mossel Bay is an important aggregation site for this life-history stage.
(2013) Fine scale movements and activity areas of white sharks (Carcharodon carcharias) in Mossel Bay, South Africa
Jewell, Johnson, Gennari, Bester (2013)
Previous work on white sharks indicate the species show seasonally limited movement patters, at certain aggregation sites small areas may play vital roles in the life history of a large amount of the population. Acoustic telemetry was used to estimate habitat use of white sharks, Carcharodon carcharias, while aggregating at Mossel Bay, South Africa. Total range of all shark tracks combined accumulated 782 h and covered an area of 93.5 km2 however, within this range, sharks were found to highly utilise a core habitat (50 % Kernel, K50) of just 1.05 km2over a reef system adjacent to a river mouth. Individual tracks revealed additional core habitats, some of which were previously undocumented and one adjacent to a commercial harbor. Much was found to be dependent on the size of the shark, with larger sharks (>400 cm) occupying smaller activity areas than subadult (300–399 cm) and juvenile (<300 cm) conspecifics, while Index of Reuse (IOR) and Index of Shared Space (IOSS) were both found to increase with shark size. Such results provide evidence that larger white sharks are more selective in habitat use, which indicates they have greater experience within aggregation sites. Furthermore, the focused nature of foraging means spatially restricted management strategies would offer a powerful tool to aid enforcement of current protective legislation for the white shark in similar environments of limited resources and capacity.
(2012) Accuracy of Using Visual Identification of White Sharks to Estimate Residency Patterns.
Delaney, Johnson, Bester, Gennari (2012)
Determining the residency of an aquatic species is important but challenging and it remains unclear what is the best sampling methodology. Photo-identification has been used extensively to estimate patterns of animals’ residency and is arguably the most common approach, but it may not be the most effective approach in marine environments. To examine this, in 2005, we deployed acoustic transmitters on 22 white sharks (Carcharodon carcharias) in Mossel Bay, South Africa to quantify the probability of detecting these tagged sharks by photo-identification and different deployment strategies of acoustic telemetry equipment. Using the data collected by the different sampling approaches (detections from an acoustic listening station deployed under a chumming vessel versus those from visual sightings and photo-identification), we quantified the methodologies’ probability of detection and determined if the sampling approaches, also including an acoustic telemetry array, produce comparable results for patterns of residency. Photo-identification had the lowest probability of detection and underestimated residency. The underestimation is driven by various factors primarily that acoustic telemetry monitors a large area and this reduces the occurrence of false negatives. Therefore, we propose that researchers need to use acoustic telemetry and also continue to develop new sampling approaches as photo-identification techniques are inadequate to determine residency. Using the methods presented in this paper will allow researchers to further refine sampling approaches that enable them to collect more accurate data that will result in better research and more informed management efforts and policy decisions.
(2011) Effects of Smart Position Only (SPOT) Tag Deployment on White Sharks Carcharodon carcharias in South Africa.
Jewell, Wcisel, Gennari, Towner, Bester, Johnson, Singh (2011)
(2011) Vagrant Southern Elephant Seal and Human Disturbance in Mossel Bay, South Africa.
Mertz & Bester (2011)
An opportunistic observational study on human disturbance of a vagrant southern elephant seal that was hauled out on a tourist beach in Mossel Bay, South Africa, is presented. Incidences of pedestrians ignoring signage and the demarcation barrier around the seal raise questions about the management of such haulout events, pubic safety and the effects of disturbance.
(2011) Distribution and abundance of humpback whales, Megaptera novaeangliae, off the coast of Mozambique.
Findlay, Meyer, Elwen, Kotze, Johnson, Truter, Uamusse, Sitoe, Wilke, Kerwath, Swanson, Staverees, Van Derwesthuizen (2011)
Humpback whales within the southwestern Indian Ocean undertake annual migrations from summer Antarctic/Southern Ocean feeding grounds to winter breeding grounds in the tropical and sub-tropical coastal waters of Mozambique, Madagascar and the central Mozambique Channel Islands. Little is known of the inter-relationship of humpback whales on each of these wintering grounds, or the inter-relationship of these wintering grounds with the summer Antarctic feeding grounds. A line-transect survey of cetacean species was carried out in Mozambique coastal waters between Cabo Inhaca (26°00’S, 33°05’E) and just north of Mozambique Island (14°26’S, 40°53’E) and between the 20 and 200m isobaths, over the period 26 August to 7 September 2003. The majority (98.1%) of 951.8 n.miles of search effort carried out on this survey was in passing mode due to the high densities of whales encountered. Humpback whales were the only large whales to be identified and the distribution of 691 sightings of an estimated 1,130 individual humpback whales and 132 sightings of an estimated 154 large unidentified whales show distribution throughout the survey region. Two sightings of individual small whales were made in the region of Inhambane. In general, higher than expected sighting densities (based on survey effort) were recorded in the region between Cabo Inhaca and Xai-Xai, and in the region of the Pantaloon and David Shoals to the north east of Quelimane. Lower than expected sighting densities were recorded over the Sofala Banks. No distribution trends could be ascribed to environmental parameters, apart from whales being distributed in waters of higher salinities than expected, possibly due to turbidity associated with low salinity water arising from river input. Groups containing a cow and calf pair were distributed across the entire region surveyed. Analyses of unstratified data result in a total abundance estimate of 6,808 (CV = 0.14) humpback and unidentified whales in the 14,029.5 n.mile2 area surveyed. As a result of the differences in width of the coastal shelf area along the coast of Mozambique, the line transect survey data were further analysed in four strata. Pooling of estimates over these four strata results in a total abundance of 6,664 whales (CV = 0.16), with highest densities in the southernmost stratum and the lowest densities in the narrow shelf region across the Sofala Banks. Similar analyses of humpback whales only resulted in abundance estimates of 5,930 (CV = 0.15) (unstratified data) and 5,965 whales (CV = 0.17) (data analysed by four strata). Although not directly comparable due to differing survey platforms, these estimates indicate the population to have increased since previous surveys in the early 1990s.
Shark cage diving
Come join Blue Wilderness shark cage diving at Durban’s Aliwal Shoal. Open to all ages and no qualifications needed!
Swim with Sharks
CoJoin us for a ‘cageless’ snorkel with sharks. Immerse yourself into the world of sharks at Durban’s Aliwal shoal