Environmental Influences on the Abundance and Sexual Composition of White Sharks Carcharodon carcharias in Gansbaai, South Africa

Towner, Alison V.; Underhill, Les G.; Jewell, Oliver J. D.; Smale, M. J.

doi:10.1371/journal.pone.0071197

Cited by 35 publications

(20 citation statements)

References 63 publications

(61 reference statements)

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“…The first difference to be considered is that between mature and immature females: The former showed a clear preference for surface behaviours such as PAR, CLI, and HA, whereas the latter preferred depth behaviours such as VA. This could be explained in light of the possible differences in habitat usage capacity that could serve to minimize food competition, as observed in other contexts (Harasti, Lee, Bruce, Gallen, & Bradford, ; Towner, Underhill, Jewell, & Smale, ).…”

Section: Discussionmentioning

confidence: 89%

The surface behaviour of white sharks during ecotourism: A baseline for monitoring this threatened species around Guadalupe Island, Mexico

Becerril‐García

Hoyos-Padilla

Micarelli³

et al. 2019

Aquatic Conservation

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1. Cage diving is the most important activity for the sustainable use of white sharks (Carcharodon carcharias). However, information related to their behaviour during ecotourism is scarce.2. This study provides useful information for monitoring C. carcharias during cagediving activities around Guadalupe Island, Mexico. Surface behaviour of 106 white sharks was recorded for 87 days on-board six cage-diving boats in 2012, 2013, and 2014.3. Of the observed sharks, 63% were immature specimens (n = 67) and 37% were considered mature (n = 39). Seventy-one per cent were males (n = 75) and 29% were females (n = 31). 4.Interactions were classified into one of the 11 behaviours: parading, close inspection, horizontal attack, vertical attack, bait catching, feeding, not feeding, buoy catching, encounter, escape, and staying. 5. Parading, close inspections, and horizontal attacks were performed more often by mature males, whereas immature females performed more vertical attacks, with no differences between mature and immature males. 6. A total of 1,542 ethograms were registered. Each ethogram consisted on average of 6.3 ± 5.6 behaviours with a significant transitional pattern from horizontal attacks to parading and close inspections, and from vertical and horizontal attacks to bait being caught. 7. A pattern related to feeding in a simple stimulus response reflex was observed. The shark's length seems to play an important role in the efficiency of the attacks, presumably resulting from the experience of mature individuals. Intentional feeding should be avoided to prevent negative effects related to ecotourism.8. This study constitutes a baseline for future research on white shark behaviour. It can be applied in other regions regardless of environmental conditions, quantity and size of the boats, and types of bait. Using this standard method could improve the monitoring, management, and conservation of this vulnerable species.

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Section: Discussionmentioning

confidence: 89%

The surface behaviour of white sharks during ecotourism: A baseline for monitoring this threatened species around Guadalupe Island, Mexico

Becerril‐García

Hoyos-Padilla

Micarelli³

et al. 2019

Aquatic Conservation

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“…Eight cage‐diving operators are permitted to anchor around the reefs at Dyer Island and Joubertsdam (Towner et al . ). Several other rocky reef and kelp forest structures exist within the bay.…”

Section: Methodsmentioning

confidence: 97%

“…The reef is characterized by rocky patch reefs interspersed with gullies and patches of sandy bottom. Eight cagediving operators are permitted to anchor around the reefs at Dyer Island and Joubertsdam (Towner et al 2013). Several other rocky reef and kelp forest structures exist within the bay.…”

Section: S T U D Y S I T Ementioning

confidence: 99%

Sex‐specific and individual preferences for hunting strategies in white sharks

et al. 2016

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Summary 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.

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“…The estuary was closed during the following periods: January-July 2009, December 2009-October 2010, December 2010-July 2011, and October 2011-June 2012 and was manually opened each time (Anchor Environmental, 2010). Sea surface temperature in the study area has been described by Towner, Underhill, Jewell, & Smale (2013), who showed that the annual mean SST was 14.9°C (mean monthly temperatures ranging from 13.5°C to 16.2°C) without any strong seasonal patterns, but with short periods of cold water fluctuation due to upwelling in summer driven by the south-easterly winds (Roberts, 2005). The prevailing wind direction shifts throughout the year: in December-February (summer) winds are predominantly southerly or south-easterly, in March-May (autumn) they are southerly, south-easterly, or north-westerly, in June-August (winter) they are north-westerly, south-easterly, or south-westerly, and in September-November (spring) they are southeasterly, southerly, or south-westerly (Law, 1999).…”

Section: Study Areamentioning

confidence: 99%

The Use of Data from a Platform of Opportunity (Whale Watching) to Study Coastal Cetaceans On the Southwest Coast of South Africa

Vinding¹,

Bester²,

Kirkman³

et al. 2015

Tourism in Marine Environments

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Effective conservation management requires information on wildlife abundance and distribution. Platforms of opportunity, including whale-watching vessels (WWV), can provide inexpensive and valuable information particularly in data deficient areas. This study analyzed over 5,500 cetacean encounters from more than 2,500 trips over 10 years by a WWV in the Western Cape, South Africa. Results were twofold: 1) providing spatial and temporal distribution patterns of the five main cetacean species for the area (southern right, humpback, and Bryde's whales, Indo-Pacific bottlenose and Indian Ocean humpback dolphins) and the first long-term, year-round data for this area; 2) showing that regularly recorded opportunistic encounters from a WWV constitute an important source of baseline information. Caveats and limitations of data from WWV are discussed and advice regarding data collection from platforms of opportunity is provided. Particularly, the lack of effort data and of clearly defined behavioral categories is emphasized and standardization of guidelines for data collection methods worldwide is suggested.

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Environmental Influences on the Abundance and Sexual Composition of White Sharks Carcharodon carcharias in Gansbaai, South Africa

Cited by 35 publications

References 63 publications

The surface behaviour of white sharks during ecotourism: A baseline for monitoring this threatened species around Guadalupe Island, Mexico

The surface behaviour of white sharks during ecotourism: A baseline for monitoring this threatened species around Guadalupe Island, Mexico

Sex‐specific and individual preferences for hunting strategies in white sharks

The Use of Data from a Platform of Opportunity (Whale Watching) to Study Coastal Cetaceans On the Southwest Coast of South Africa

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