Pessimistic assessment of white shark population status in South Africa: Comment on Andreotti et al. (2016)

Irion, Dylan T.; Noble, Leslie R.; Kock, Alison A.; Gennari, Enrico; Dicken, ML; Hewitt, Adrian M.; Towner, Alison V.; Booth, Anthony J.; Smale, M. J.; Cliff, Geremy

doi:10.3354/meps12283

Cited by 14 publications

(7 citation statements)

References 28 publications

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“…The reasons for the white shark population declines documented at Seal Island since 2015, combined with prolonged periods of disappearances in our surveys during 2017 and 2018, remain unknown. It is possible these patterns reflect population-level declines for the region, for example, from over-fishing or habitat loss, as suggested from mark-recapture, photo-ID and genetic analysis 19–21 . It is also possible that False Bay’s white sharks have shifted their distributional range elsewhere due to shifts in environmental conditions or prey 22 .…”

Section: Introductionmentioning

confidence: 99%

Disappearance of white sharks leads to the novel emergence of an allopatric apex predator, the sevengill shark

Hammerschlag

Williams²,

Fallows³

et al. 2019

Sci Rep

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Despite global declines of apex predatory sharks, evidence for ecosystem consequences remains limited and debated. This is likely a result of both the logistical difficulties of measuring such processes in marine systems and also due to shifting baselines, whereby the ecosystem changes have occurred prior to monitoring. Between 2000–2018, we conducted standardized monitoring of white shark (Carcharodon carcharias) abundance patterns (N = 6,333 shark sightings) and predatory activity (N = 8,076 attacks on seals) at Seal Island, a Cape fur seal (Arctocephalus pusillus pusillus) colony in False Bay, South Africa. Over the 18-year study, declines in white shark abundance and attack rates were documented between 2015–2018, with anomalous lows occurring in 2017 and 2018. This included prolonged periods of complete white shark absence from Seal Island. The disappearance of white sharks from Seal Island coincided with the unprecedented appearance of sevengill sharks (Notorynchus cepedianus; N = 120 sightings), an otherwise allopatric kelp-associated apex predator in False Bay. We also recorded a sevengill shark attacking a live seal in the absence of white sharks. These data provide empirical evidence for behavioral shifts in an allopatric marine predator following the decline and disappearance of white sharks from a foraging site. This study demonstrates the importance of historical data and long-term monitoring for disentangling ecological consequences of apex predator declines.

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Section: Introductionmentioning

confidence: 99%

Disappearance of white sharks leads to the novel emergence of an allopatric apex predator, the sevengill shark

Hammerschlag

Williams²,

Fallows³

et al. 2019

Sci Rep

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“…The biomass of Great white shark was estimated using a point estimate of 438 individuals (Andreotti et al 2016), this value is considered an underestimate of the population size (Irion et al 2017) and previous studies estimated the white shark population off the South African coast from 1989 to 1993 to range between 839 and 1 843 individuals, with a mean of 1 279 (Cliff et al 1996). Since Andreotti et al (2016) is the most recent and complete assessment of white shark population in South Africa, this estimate was used here.…”

Section: Benthic Elasmobranchs (30) Pelagic Elasmobranchs (31) and Ap...mentioning

confidence: 99%

Supporting marine spatial planning with an ecosystem model of Algoa Bay, South Africa

Ortega-Cisneros

Weigum

Chalmers

et al. 2022

African Journal of Marine Science

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The P/B and P/Q values for meso-and macrozooplankton were based on Hutchings et al. (1991), and the P/B value for microzooplankton from Hutchings et al. (1995). The Q/B ratio of microzooplankton and the diet of the micro-, meso-and macrozooplankton were derived from the Southern Benguela model (Shannon et al. 2020). For gelatinous zooplankton, the biomass, P/B and Q/B values from the Southern Benguela model (Shannon et al. 2020) were used. Benthos (8, 9)Meiobenthos and macrobenthos biomass was estimated by EwE using the P/B, Q/B and EE (0.95) values for the southern Benguela model (Shannon et al. 2020). Diet information was also derived from this model. Chokka squid (10) and other cephalopods (11)The biomass of chokka squid was derived from the demersal trawl surveys for the south coast of South Africa using information from years 2010, 2011 and 2014 for the depth stratum 0-100 m. The abundance estimate (in tons) was divided by the stratum area (nm 2 ), and then converted from t nm 2 to t km 2 . The average over the 2010-2014 period was input in the model. The P/B and P/Q values from the southern Benguela model were used. Diet information was obtained from Sauer and Lipiński (1991).In terms of other cephalopods, Augustyn et al. (1995) reported that the most common species of Sepioidea in the

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“…Trends or population indices in white shark populations are much easier to identify than absolute population sizes (e.g., Hewitt et al, 2018); even methods that might be considered unreliable for a true population estimate can provide a trend if they are periodically conducted and compared to historical results from the same method. A better understanding of the demography of white shark populations and estimates of mortality across life-history stages (e.g., Benson et al, 2018) is also needed to reduce uncertainties in modeling outputs (Burgess et al, 2014;Irion et al, 2017). Methods that use an integrated approach combining different methods such as catch statistics from beach protection programs or fisheries bycatch, markrecapture based on photo-identification or electronic tagging, and genetic analysis (e.g., close-kin genetics) are recommended to overcome sampling biases and modeling assumptions (Dewar et al, 2013;Irion et al, 2017;Benson et al, 2018).…”

Section: Organismal Biologymentioning

confidence: 99%

“…A better understanding of the demography of white shark populations and estimates of mortality across life-history stages (e.g., Benson et al, 2018) is also needed to reduce uncertainties in modeling outputs (Burgess et al, 2014;Irion et al, 2017). Methods that use an integrated approach combining different methods such as catch statistics from beach protection programs or fisheries bycatch, markrecapture based on photo-identification or electronic tagging, and genetic analysis (e.g., close-kin genetics) are recommended to overcome sampling biases and modeling assumptions (Dewar et al, 2013;Irion et al, 2017;Benson et al, 2018). These methods should be applied across regions and populations to allow for comparisons.…”

Section: Organismal Biologymentioning

confidence: 99%

Future Research Directions on the “Elusive” White Shark

et al. 2018

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Pessimistic assessment of white shark population status in South Africa: Comment on Andreotti et al. (2016)

Cited by 14 publications

References 28 publications

Disappearance of white sharks leads to the novel emergence of an allopatric apex predator, the sevengill shark

Disappearance of white sharks leads to the novel emergence of an allopatric apex predator, the sevengill shark

Supporting marine spatial planning with an ecosystem model of Algoa Bay, South Africa

Future Research Directions on the “Elusive” White Shark

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