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  1. Article ; Online: Sex and Size Influence the Spatiotemporal Distribution of White Sharks, With Implications for Interactions With Fisheries and Spatial Management in the Southwest Indian Ocean

    Alison A. Kock / Amanda T. Lombard / Ryan Daly / Victoria Goodall / Michael Meÿer / Ryan Johnson / Chris Fischer / Pieter Koen / Dylan Irion / Enrico Gennari / Alison Towner / Oliver J. D. Jewell / Charlene da Silva / Matthew L. Dicken / Malcolm J. Smale / Theoni Photopoulou

    Frontiers in Marine Science, Vol

    2022  Volume 9

    Abstract: Human activities in the oceans increase the extinction risk of marine megafauna. Interventions require an understanding of movement patterns and the spatiotemporal overlap with threats. We analysed the movement patterns of 33 white sharks (Carcharodon ... ...

    Abstract Human activities in the oceans increase the extinction risk of marine megafauna. Interventions require an understanding of movement patterns and the spatiotemporal overlap with threats. We analysed the movement patterns of 33 white sharks (Carcharodon carcharias) satellite-tagged in South Africa between 2012 and 2014 to investigate the influence of size, sex and season on movement patterns and the spatial and temporal overlap with longline and gillnet fisheries and marine protected areas (MPAs). We used a hidden Markov model to identify ‘resident’ and ‘transient’ movement states and investigate the effect of covariates on the transition probabilities between states. A model with sex, total length and season had the most support. Tagged sharks were more likely to be in a resident state near the coast and a transient state away from the coast, while the probability of finding a shark in the transient state increased with size. White sharks moved across vast areas of the southwest Indian Ocean, emphasising the need for a regional management plan. White sharks overlapped with longline and gillnet fisheries within 25% of South Africa’s Exclusive Economic Zone and spent 15% of their time exposed to these fisheries during the study period. The demersal shark longline fishery had the highest relative spatial and temporal overlap, followed by the pelagic longline fishery and the KwaZulu-Natal (KZN) shark nets and drumlines. However, the KZN shark nets and drumlines reported the highest white shark catches, emphasising the need to combine shark movement and fishing effort with reliable catch records to assess risks to shark populations accurately. White shark exposure to shark nets and drumlines, by movement state, sex and maturity status, corresponded with the catch composition of the fishery, providing support for a meaningful exposure risk estimate. White sharks spent significantly more time in MPAs than expected by chance, likely due to increased prey abundance or less disturbance, suggesting that MPAs can benefit ...
    Keywords conservation ; satellite tagging ; movement states ; marine protected area (MPA) ; Carcharodon carcharias ; Science ; Q ; General. Including nature conservation ; geographical distribution ; QH1-199.5
    Subject code 333
    Language English
    Publishing date 2022-04-01T00:00:00Z
    Publisher Frontiers Media S.A.
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article ; Online: Deep learning accurately predicts white shark locomotor activity from depth data

    Zac Yung-Chun Liu / Jerry H. Moxley / Paul Kanive / Adrian C. Gleiss / Thom Maughan / Larry Bird / Oliver J. D. Jewell / Taylor K. Chapple / Tyler Gagne / Connor F. White / Salvador J. Jorgensen

    Animal Biotelemetry, Vol 7, Iss 1, Pp 1-

    2019  Volume 13

    Abstract: Abstract Background The study of bioenergetics, kinematics, and behavior in free-ranging animals has been transformed through the increasing use of biologging devices that sample motion intensively with high-resolution sensors. Overall dynamic body ... ...

    Abstract Abstract Background The study of bioenergetics, kinematics, and behavior in free-ranging animals has been transformed through the increasing use of biologging devices that sample motion intensively with high-resolution sensors. Overall dynamic body acceleration (ODBA) derived from biologging tags has been validated as a proxy of locomotor energy expenditure has been calibrated in a range of terrestrial and aquatic taxa. The increased temporal resolution required to discern fine-scale processes and infer energetic expenditure, however, is associated with increased power and memory requirements, as well as the logistical challenges of recovering data from archival instruments. This limits the duration and spatial extent of studies, potentially excluding relevant ecological processes that occur over larger scales. Method Here, we present a procedure that uses deep learning to estimate locomotor activity solely from vertical movement patterns. We trained artificial neural networks (ANNs) to predict ODBA from univariate depth (pressure) data from two free-swimming white sharks (Carcharodon carcharias). Results Following 1 h of training data from an individual shark, ANN enabled robust predictions of ODBA from 1 Hz pressure sensor data at multiple temporal scales. These predictions consistently out-performed a null central-tendency model and generalized predictions more accurately than other machine learning techniques tested. The ANN prediction accuracy of ODBA integrated overtime periods ≥ 10 min was consistently high (~ 90% accuracy, > 10% improvement over null) for the same shark and equivalently generalizable across individuals (> 75% accuracy). Instantaneous ODBA estimates were more variable (R 2 = 0.54 for shark 1, 0.24 for shark 2). Prediction accuracy was insensitive to the volume of training data, no observable gains were achieved in predicting 6 h of test data beyond 1–3 h of training. Conclusions Augmenting simple depth metrics with energetic and kinematic information from comparatively short-lived, ...
    Keywords White shark ; Biologging ; Machine learning ; Locomotion ; Dynamic body acceleration ; Data augmentation ; Ecology ; QH540-549.5 ; Animal biochemistry ; QP501-801
    Subject code 006
    Language English
    Publishing date 2019-08-01T00:00:00Z
    Publisher BMC
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article ; Online: Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa.

    Alison V Towner / Les G Underhill / Oliver J D Jewell / Malcolm J Smale

    PLoS ONE, Vol 8, Iss 8, p e

    2013  Volume 71197

    Abstract: The seasonal occurrence of white sharks visiting Gansbaai, South Africa was investigated from 2007 to 2011 using sightings from white shark cage diving boats. Generalized linear models were used to investigate the number of great white sharks sighted per ...

    Abstract The seasonal occurrence of white sharks visiting Gansbaai, South Africa was investigated from 2007 to 2011 using sightings from white shark cage diving boats. Generalized linear models were used to investigate the number of great white sharks sighted per trip in relation to sex, month, sea surface temperature and Multivariate El Niño/Southern Oscillation (ENSO) Indices (MEI). Water conditions are more variable in summer than winter due to wind-driven cold water upwelling and thermocline displacement, culminating in colder water temperatures, and shark sightings of both sexes were higher during the autumn and winter months (March-August). MEI, an index to quantify the strength of Southern Oscillation, differed in its effect on the recorded numbers of male and female white sharks, with highly significant interannual trends. This data suggests that water temperature and climatic phenomena influence the abundance of white sharks at this coastal site. In this study, more females were seen in Gansbaai overall in warmer water/positive MEI years. Conversely, the opposite trend was observed for males. In cool water years (2010 to 2011) sightings of male sharks were significantly higher than in previous years. The influence of environmental factors on the physiology of sharks in terms of their size and sex is discussed. The findings of this study could contribute to bather safety programmes because the incorporation of environmental parameters into predictive models may help identify times and localities of higher risk to bathers and help mitigate human-white shark interactions.
    Keywords Medicine ; R ; Science ; Q
    Subject code 590
    Language English
    Publishing date 2013-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article ; Research data: (with research data) Sex‐specific and individual preferences for hunting strategies in white sharks

    Towner, Alison V / Vianey Leos‐Barajas / Roland Langrock / Robert S. Schick / Malcolm J. Smale / Tami Kaschke / Oliver J. D. Jewell / Yannis P. Papastamatiou

    Functional ecology. 2016 Aug., v. 30, no. 8

    2016  

    Abstract: Fine‐scale predator movements may be driven by many factors including sex, habitat and distribution of resources. There may also be individual preferences for certain movement strategies within a population which can be hard to quantify. Within top ... ...

    Abstract Fine‐scale predator movements may be driven by many factors including sex, habitat and distribution of resources. There may also be individual preferences for certain movement strategies within a population which can be hard to quantify. Within top predators, movements are also going to be directly related to the mode of hunting, for example sit‐and‐wait or actively searching for prey. Although there is mounting evidence that different hunting modes can cause opposing trophic cascades, there has been little focus on the modes used by top predators, especially those in the marine environment. Adult white sharks (Carcharhodon carcharias) are well known to forage on marine mammal prey, particularly pinnipeds. Sharks primarily ambush pinnipeds on the surface, but there has been less focus on the strategies they use to encounter prey. We applied mixed hidden Markov models to acoustic tracking data of white sharks in a coastal aggregation area in order to quantify changing movement states (area‐restricted searching (ARS) vs. patrolling) and the factors that influenced them. Individuals were re‐tracked over multiple days throughout a month to see whether state‐switching dynamics varied or if individuals preferred certain movement strategies. Sharks were more likely to use ARS movements in the morning and during periods of chumming by ecotourism operators. Furthermore, the proportion of time individuals spent in the two different states and the state‐switching frequency, differed between the sexes and between individuals. Predation attempts/success on pinnipeds were observed for sharks in both ARS and patrolling movement states and within all random effects groupings. Therefore, white sharks can use both a ‘sit‐and‐wait’ (ARS) and ‘active searching’ (patrolling) movements to ambush pinniped prey on the surface. White sharks demonstrate individual preferences for fine‐scale movement patterns, which may be related to their use of different hunting modes. Marine top predators are generally assumed to use only one type of hunting mode, but we show that there may be a mix within populations. As such, individual variability should be considered when modelling behavioural effects of predators on prey species.
    Keywords Markov chain ; acoustics ; adults ; ecotourism ; habitats ; marine environment ; marine mammals ; models ; predation ; predators ; sharks
    Language English
    Dates of publication 2016-08
    Size p. 1397-1407.
    Publishing place John Wiley & Sons, Ltd
    Document type Article ; Research data
    Note JOURNAL ARTICLE
    ZDB-ID 2020307-X
    ISSN 1365-2435 ; 0269-8463 ; 0269-8463
    ISSN (online) 1365-2435
    ISSN 0269-8463
    DOI 10.1111/1365-2435.12613
    Database NAL-Catalogue (AGRICOLA)

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  5. Article ; Online: Correction

    Alison V. Towner / Michelle A. Wcisel / Ryan R. Reisinger / David Edwards / Oliver J. D. Jewell

    PLoS ONE, Vol 8, Iss

    Gauging the Threat: The First Population Estimate for White Sharks in South Africa Using Photo Identification and Automated Software.

    2013  Volume 6

    Keywords Medicine ; R ; Science ; Q
    Language English
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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    Inter-library loan at ZB MED

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  6. Article ; Online: Correction

    Alison V. Towner / Michelle A. Wcisel / Ryan R. Reisinger / David Edwards / Oliver J. D. Jewell

    PLoS ONE, Vol 8, Iss

    Gauging the Threat: The First Population Estimate for White Sharks in South Africa Using Photo Identification and Automated Software

    2013  Volume 6

    Keywords Medicine ; R ; Science ; Q
    Language English
    Publishing date 2013-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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    Inter-library loan at ZB MED

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  7. Article ; Online: Gauging the threat

    Alison V Towner / Michelle A Wcisel / Ryan R Reisinger / David Edwards / Oliver J D Jewell

    PLoS ONE, Vol 8, Iss 6, p e

    the first population estimate for white sharks in South Africa using photo identification and automated software.

    2013  Volume 66035

    Abstract: South Africa is reputed to host the world's largest remaining population of white sharks, yet no studies have accurately determined a population estimate based on mark-recapture of live individuals. We used dorsal fin photographs (fin IDs) to identify ... ...

    Abstract South Africa is reputed to host the world's largest remaining population of white sharks, yet no studies have accurately determined a population estimate based on mark-recapture of live individuals. We used dorsal fin photographs (fin IDs) to identify white sharks in Gansbaai, South Africa, from January 2007-December 2011. We used the computer programme DARWIN to catalogue and match fin IDs of individuals; this is the first study to successfully use the software for white shark identification. The programme performed well despite a number of individual fins showing drastic changes in dorsal fin shape over time. Of 1682 fin IDs used, 532 unique individuals were identified. We estimated population size using the open-population POPAN parameterisation in Program MARK, which estimated the superpopulation size at 908 (95% confidence interval 808-1008). This estimated population size is considerably larger than those described at other aggregation areas of the species and is comparable to a previous South African population estimate conducted 16 years prior. Our assessment suggests the species has not made a marked recovery since being nationally protected in 1991. As such, additional international protection may prove vital for the long-term conservation of this threatened species.
    Keywords Medicine ; R ; Science ; Q
    Subject code 333
    Language English
    Publishing date 2013-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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    Inter-library loan at ZB MED

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  8. Article ; Online: Correction

    Alison V. Towner / Michelle A. Wcisel / Ryan R. Reisinger / David Edwards / Oliver J. D. Jewell

    PLoS ONE, Vol 8, Iss

    Gauging the Threat: The First Population Estimate for White Sharks in South Africa Using Photo Identification and Automated Software

    2013  Volume 6

    Keywords Medicine ; R ; Science ; Q
    Language English
    Publishing date 2013-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

    Full text online

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    Inter-library loan at ZB MED

    Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

  9. Article ; Online: Correction

    Alison V. Towner / Michelle A. Wcisel / Ryan R. Reisinger / David Edwards / Oliver J. D. Jewell

    PLoS ONE, Vol 8, Iss

    Gauging the Threat: The First Population Estimate for White Sharks in South Africa Using Photo Identification and Automated Software.

    2013  Volume 6

    Keywords Medicine ; R ; Science ; Q
    Language English
    Publishing date 2013-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

    Full text online

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    Inter-library loan at ZB MED

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  10. Article ; Online: Effects of Smart Position Only (SPOT) tag deployment on white sharks Carcharodon carcharias in South Africa.

    Oliver J D Jewell / Michelle A Wcisel / Enrico Gennari / Alison V Towner / Marthán N Bester / Ryan L Johnson / Sarika Singh

    PLoS ONE, Vol 6, Iss 11, p e

    2011  Volume 27242

    Abstract: 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 ... ...

    Abstract 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.
    Keywords Medicine ; R ; Science ; Q
    Language English
    Publishing date 2011-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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