Shark Diving Unlimited

Gans, South Africa

Shark Diving Unlimited

Gans, South Africa

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Andreotti S.,Stellenbosch University | Rutzen M.,Shark Diving Unlimited | Wesche P.L.,University of Johannesburg | O'Connell C.P.,University of Massachusetts Dartmouth | And 3 more authors.
African Journal of Marine Science | Year: 2014

The white shark Carcharodon carcharias was one of the first elasmobranch species where photo identification was used to identify unique individuals. In this study, we propose guidelines that improve the current photo identification technique for white sharks by presenting a novel categorisation system. Using this method, a high-resolution photograph of the dorsal fin is placed on a standardised three-section grid. Notches associated with the trailing edge of the fin are counted and scored within each grid section. The number of notches in each grid section is then used to produce a three-part code that is utilised to systematically organise the individuals into a database. Our proposed system was tested on sharks photographed in the sampling area over a 27-month period (4 398 photographs) and the method significantly reduced the search time associated with identifying resighted individuals. Using the notches code, we were able to identify 426 different C. carcharias within the Dyer Island Nature Reserve (South Africa). Due to the inherent ease of use, the accuracy associated with this method, and the ability to 'resight' individuals rapidly within a large photographic database, this non-invasive technique presents a validated and feasible alternative for future white shark photo identification studies. © 2014 Copyright © NISC (Pty) Ltd.

O'Connell C.P.,University of Massachusetts Dartmouth | O'Connell C.P.,OSeas Conservation Foundation | Andreotti S.,Stellenbosch University | Rutzen M.,Shark Diving Unlimited | And 3 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2014

The white shark (Carcharodon carcharias) is an apex predator and is a protected species that suffers from several sources of anthropogenic mortality, such as shark nets. Shark nets are devices used to minimize the interaction between beachgoers and potentially dangerous sharks; however, these nets have negatively impacted local and migratory shark populations, in addition to killing substantial quantities of other marine organisms. To address this issue, the present study developed and examined the effects of an alternative technology (the "Sharksafe" barrier) composed of two stimuli: (1) visual-artificial-kelp and (2) electrosensory-magnets, on C. carcharias behavior. Generalized linear mixed effect models were used to test hypotheses pertaining to the effects of treatment type, exposure quantity (i.e. habituation), conspecific density, and water visibility on shark behavior. Analyses based on forty-nine, one-hour trials illustrate that the swim patterns of all sixty-three individual C. carcharias was altered in the presence of the artificial kelp-the procedural control region, and the magnetic kelp-the magnetic region of the barrier (i.e. procedural control and magnetic regions reduced entrance frequency and increased avoidance and pass around frequency). Also, preliminary observations illustrated that the barrier had no observable impact on Cape fur seal (Arctocephalus pusillus pusillus) behavior. The C. carcharias-specific repellency associated with the Sharksafe barrier and the ability of the barrier to withstand harsh environmental conditions warrant future experiments to assess its exclusion capabilities on predatory sharks and possible application to replace shark nets. © 2014 Elsevier B.V.

O'Connell C.P.,University of Massachusetts Dartmouth | Andreotti S.,Stellenbosch University | Rutzen M.,Shark Diving Unlimited | MeYer M.,Branch Oceans and Coasts | He P.,University of Massachusetts Dartmouth
Ocean and Coastal Management | Year: 2014

Beach nets are preventative devices that are utilized to minimize the potential interaction between a beachgoer and a predatory shark. One species, the great white shark (Carcharodon carcharias), the focal species for the present study and a protected species in South African waters, is often killed in beach nets within the KwaZulu-Natal (KZN) region. To address the issue of C.carcharias capture in beach nets and to reduce mortality of this species, two related experiments were carried out: the bait experiment and the magnetic-control barrier experiment. Both experiments were aimed to determine the effect of permanent magnets on C.carcharias. During the bait experiment, a total of twenty C.carcharias interacted with the control and magnetic apparatuses. The results indicate that avoidance and feeding behaviors were significantly associated with treatment type, suggesting that permanent magnets had C.carcharias deterrent capabilities. In addition, it was demonstrated that the likelihood of an avoidance behavior on the magnet-associated baits was not significantly correlated with water visibility or conspecific density. For the second experiment, results from stage I of the magnetic-control barrier experiment indicate that behavior was not associated with treatment zo≠ however, stage II indicated that behavior was significantly associated with treatment type. Results from the magnetic-control barrier experiment clearly demonstrate that although a visual barrier, such as the procedural control barrier, may be sufficient to deter C.carcharias from an area, the addition of permanent magnets provide additional successful deterrence of C.carcharias. This study demonstrates that C.carcharias are sensitive to strong permanent magnetic fields; therefore a large-scale experiment with a substantially greater sample size is warranted to investigate the potential of a non-invasive magnetic barrier to replace detrimental beach nets in KwaZulu-Natal, South Africa. © 2012 Elsevier Ltd.

Andreotti S.,Stellenbosch University | Von Der Heyden S.,Stellenbosch University | Henriques R.,Stellenbosch University | Rutzen M.,Shark Diving Unlimited | And 3 more authors.
Journal of Biogeography | Year: 2016

Aim: To determine the genetic structure of the white shark population around the South African coastline and, by including data from animals sampled elsewhere in the world, to provide new insights into white shark evolution at the global scale. Methods: Mitochondrial and microsatellite analyses were performed on 302 free-ranging white sharks collected from five sites along the South African coastline. This was augmented with 58 GenBank sequences originating from five distinct global populations. Genetic diversity, local population sub-structuring analyses and global phylogeographical patterns were determined. Results: Four mtDNA haplotypes restricted to South Africa were recovered. One common haplotype was shared by 89% of all the individuals and was 13 bp different from the second most common haplotype shared by 10% of the remaining sharks. No local geographical sub-structuring was evident for either mtDNA or nuclear DNA. Both data sets show a remarkably low level of genetic diversity (mtDNA: h = 0.205, π = 0.0027; nDNA: Na = 7.6, Ho = 0.675). At the global scale, three distinct geographical clades were detected which could not be connected with 95% confidence in the haplotype network. Main conclusions: Results indicate that the observed South African mtDNA biogeographical pattern and diversity levels may be a consequence of a severe bottleneck or a recent colonization event from one or two sources. Globally, the population of white sharks can be differentiated into three mtDNA clades confined to (1) the Mediterranean and Indo-Pacific Oceans (Australia and California), (2) the North West Atlantic (Florida) and Indian Ocean (South Africa), and (3) a single divergent haplotype restricted to South Africa. The pattern is most likely the result of a combination of site philopatry, isolation by distance, infrequent long-distance dispersal, isolated founder events and the closure of the Isthmus of Panama. © 2015 John Wiley & Sons Ltd.

Andreotti S.,Stellenbosch University | Rutzen M.,Shark Diving Unlimited | Van Der Walt S.,Stellenbosch University | Von Der Heyden S.,Stellenbosch University | And 4 more authors.
Marine Ecology Progress Series | Year: 2016

The loss of apex marine predators has been reported to have a cascade of detrimental effects on marine ecosystems; however, the general lack of empirical data can severely limit our understanding of the ecological interactions among marine species. In this study we propose an integrated approach using mark-recapture and genetic techniques to assess population estimates of white sharks Carcharodon carcharias. Between 2009 and 2011, 4389 dorsal fin photographic identifications were collected in Gansbaai, South Africa, from 426 white sharks and used in markrecapture analyses. Saturation of new sightings occurred once 400 individuals were catalogued and the open population model POPAN suggested ranges between 353 and 522 individuals (95% confidence) and a point estimate of N = 438. Between 2010 and 2013, 302 biopsy samples were collected from 233 white sharks and used for a comparative genetic population estimate. Analyses of 14 microsatellite markers revealed a contemporary effective population size (CNe) of 333 individuals (95% CI = 247-487, pcrit = 0.02). These values were at least 52% less than those estimated in previous mark-recapture studies. Using this combination of techniques, we propose a Ne:N ratio of 0.76 for white sharks, which advances our ability to accurately make inferences on elasmobranch population numbers in general. Given the low population numbers of white sharks along the South African coastline, we predict a negative effect on the ecological stability of the marine environment in this region. © 2016 Inter-Research.

PubMed | University of Massachusetts Dartmouth, Stellenbosch University, Shark Diving Unlimited and University of Applied science
Type: Journal Article | Journal: Journal of fish biology | Year: 2015

This study employed a non-lethal measurement tool, which combined an existing photo-identification technique with a surface, parallel laser photogrammetry technique, to accurately estimate the size of free-ranging white sharks Carcharodon carcharias. Findings confirmed the hypothesis that surface laser photogrammetry is more accurate than crew-based estimations that utilized a shark cage of known size as a reference tool. Furthermore, field implementation also revealed that the photographers angle of reference and the sharks body curvature could greatly influence technique accuracy, exposing two limitations. The findings showed minor inconsistencies with previous studies that examined pre-caudal to total length ratios of dead specimens. This study suggests that surface laser photogrammetry can successfully increase length estimation accuracy and illustrates the potential utility of this technique for growth and stock assessments on free-ranging marine organisms, which will lead to an improvement of the adaptive management of the species.

News Article | February 15, 2017

The lack of a standardized procedure for collecting data about elusive and hard to find species like the great white shark has to date seriously hampered efforts to manage and protect these animals The lack of a standardized procedure for collecting data about elusive and hard to find species like the great white shark has to date seriously hampered efforts to manage and protect these animals. But now a marine biologist, an applied mathematician and a software developer from Stellenbosch University joined expertise to develop a custom-made software package, called Identifin, which may offer a solution to this problem. Dr Sara Andreotti, a marine biologist in the Department of Botany and Zoology at SU, have collected over 5000 photographic images of the dorsal fins of white sharks along the South African coastline as part of her research on the population structure of South Africa's great white sharks. This is because the trailing edge of the dorsal fin provides a unique trade, analogous to a human fingerprint. Over six years she managed to manually build a database with information on when and where an individual white shark was sighted. In those cases where she was able to collect a biopsy from the shark, the genetic information was linked to its profile. But she was doing all this manually on her personal computer. "I nearly lost my head. I quickly realised that in the long term updating the database was going to consume more and more of my time. That is when I headed over campus to the applied mathematics division and asked for help. I was stunned when they became all excited about my data," she laughs. Prof. Ben Herbst, a specialist in machine learning, and Dr Pieter Holtzhausen, a software engineer then busy with his PhD in Applied Mathematics, were literally overjoyed to be able to work with Dr Andreotti' s data base. Dr Holtzhausen explains: "We used an algorithmic technique called dynamic time-warping to match the fingerprints. With this technique, any data that can be turned into a linear sequence can be analysed. The technique is often used in speech recognition software." The image recognition software they developed, called Identifin, compares a semi-automatically drawn trace of the back edge of the dorsal fin to existing images in the database. The images in the database are then re-arranged and ranked by probability of match. If there is a match, the database photograph in the first position will be the correct one (see multimedia images). However, while working with Michael Meyer, a marine scientist from the Department of Environmental Affairs, and shark conservationist Michael Rutzen from Shark Diving Unlimited, Dr Andreotti realised that the software needed some more tweaking if it were to fit the ideal of sustaining a large database for the long-term monitoring of the white shark population. "The software had to be capable of quickly matching the fin identification of a newly photographed shark with a possible existing match in the database, and to automatically update the sharks' id catalogue. The database also had to be user-friendly and structured in such a way so that different researchers can use it over the long term," she explains. While there is still room for improvement, the success of the first trials boosted their hope that in the near future they will be able to use Identifin to monitor white shark populations on a large scale. "Previously, while at sea, I had to try and memorize which shark is which, to prevent sampling the same individual more than once. Now Identifin can take over. I will only need to download the new photographic identifications from my camera onto a small field laptop and run the software to see if the sharks currently around the boat have been sampled or not. "By knowing which sharks had not been sampled before we can focus the biopsy collections on them. This saves us both time and money when it comes to genetic analysis in the laboratory," she adds. Dr Andreotti says to date the lack of standardization of data collection has been a major limitation to combining datasets of worldwide distributed species: "We hope Identifin will offer a solution for the development of a South African and then global adaptive management plan for great white sharks." The next step is to adapt Identifin for the identification of other large marine species and help other researchers facing the same kind of struggles. Andreotti S, Rutzen M, Wesche PS, O'Connell CP, Meÿer M, Oosthuizen WH, Matthee CA (2014) A novel categorisation system to organize a large photo identification database for white sharks Carcharodon carcharias. African Journal of Marine Science 36:59-67. Available online at http://www. Andreotti S, Heyden S von der, Henriques R, Rutzen M, Meÿer M, Oosthuizen H, Matthee CA (2016) New insights into the evolutionary history of white sharks, Carcharodon carcharias. Journal of Biogeography 43:328-339. Available online at http://onlinelibrary. Andreotti S, Rutzen M, Walt S van der, Heyden S Von der, Henriques R, Meÿer M, Oosthuizen H, Matthee C (2016) An integrated mark-recapture and genetic approach to estimate the population size of white sharks in South Africa. Marine Ecology Progress Series 552:241-253. Available online at http://www.

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