Trends in sightings and population structure of white sharks, Carcharodon carcharias, at Seal Island, False Bay, South Africa, and the emigration of subadult female sharks approaching maturity

A synthesis of three decades of socio-ecological change in False Bay, South Africa: setting the scene for multidisciplinary research and management

“…This restriction was followed by rapid growth in tourism and research centered on white sharks. False Bay is used primarily by juvenile and sub-adult white sharks ranging in size from 2 to 5 m (Ferreira and Ferreira, 1996;Hewitt et al, 2018).…”

“…The population of white sharks at Seal Island has been estimated to be 723 ± 132 (standard error) individuals, with a range of 12-287 individuals estimated to be present in any year (2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) (Hewitt et al, 2018). Since 2003, shark sightings at Seal Island have exhibited annual peaks and troughs, with an overall decreasing trend in sighting rates, although this was not statistically significant (Hewitt, 2014).…”

“…Conversely, shark sightings inshore, at Muizenberg and Fish Hoek, exhibited a significant increase over a similar period (Weltz et al, 2013). Fluctuations in sighting rates remain poorly understood, but are likely related to environmental factors and associated prey availability (Weltz et al, 2013;Hewitt et al, 2018). Over the last two years (2016-2018), white shark sightings in False Bay have been the lowest on record (A.…”

Patterns of long-term climate variability and predation rates by a marine apex predator, the white shark Carcharodon carcharias

“…White shark population declines have been speculated for the region based on mark-recapture and genetic analysis (Andreotti et al 2016), although interpreted with some level of skepticism (Irion et al 2017). Further, white shark sightings have declined at Seal Island in False Bay over a 9 yr monitoring period (Hewitt et al 2018). If predation rates were reflective of white shark population trends alone, such as those suggested in the aforementioned stud-ies, it would likely manifest as prolonged long-term declines in predation rates, rather than the alternating increases and decreases observed here.…”

Future Research Directions on the “Elusive” White Shark

“…As a result, abundance data are lacking for understudied populations and reliable abundance trends are missing for most regions. 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).…”