Abstract
BackgroundUnderstanding white shark (Carcharodon carcharias) habitat use in coastal areas adjacent to large cities, is an important step when formulating potential solutions to the conservation conflict that exists between humans and large predatory sharks. In this study, we present the findings of a 2.5-year study of white shark occurrence and movement patterns adjacent to the City of Cape Town in False Bay, South Africa, with a focus on spring and summer months. Fifty-one white sharks were monitored annually at three offshore and twelve inshore sites by VR2 acoustic receivers, over 975 days from 1 May 2005 to 31 December 2007.ResultsOccurrence patterns at inshore sites during spring and summer were analysed using a generalized additive mixed model (GAMM) with a spatial term (longitude, latitude), time of day and year included as explanatory variables for site use. We found that sharks occurred more frequently at inshore sites along the northern and northwestern shores, compared to the rest of the bay, and they transitioned most frequently between four adjacent beach sites that encompass the most popular recreational water use areas in Cape Town. There was significant diel variation, with higher shark occurrence around midday, and a peak in shark occurrence in 2005, when human-shark interactions also peaked. However, we found no effect of shark size on occurrence patterns at inshore sites.ConclusionsWhite sharks showed the highest levels of occurrence at specific inshore sites between Muizenberg and Strandfontein beach, and thus inclusion of these sites within False Bay’s marine protected area (MPA) network or recognition as Ecological or Biological Significant Areas (EBSAs) should be a future consideration. These insights into white shark habitat use at inshore sites in False Bay are important for successfully applying the principles of marine spatial planning (MSP) and for making science-based policy decisions. Furthermore, this information can be used to reduce potential shark-human conflict by incorporating it into future shark safety education campaigns.
Highlights
Understanding white shark (Carcharodon carcharias) habitat use in coastal areas adjacent to large cities, is an important step when formulating potential solutions to the conservation conflict that exists between humans and large predatory sharks
Sex and size of tagged sharks A total of 53 white sharks were tagged with acoustic transmitters in False Bay between 1 May 2005 and 31 December 2007 (2005, n = 23; 2006, n = 25; 2007, n = 5)
51 sharks were included in the analysis of movement between sites, and 36 sharks were detected on the False Bay receiver array during spring and summer months between 1 May 2005 and 31 December 2007 and included in the generalized additive mixed model (GAMM) analysis (Table 1)
Summary
Understanding white shark (Carcharodon carcharias) habitat use in coastal areas adjacent to large cities, is an important step when formulating potential solutions to the conservation conflict that exists between humans and large predatory sharks. Understanding the movement and habitat use of vulnerable marine top predators is essential for devising improved conservation and management strategies [1,2,3] This is important for large predatory shark species that aggregate in coastal areas threatened by diverse. Since 2009, they have been listed as Vulnerable on the IUCN Red List of Threatened Species and protected in several countries [13] Both juvenile and sub-adult white sharks use coastal areas extensively [14,15,16,17,18,19,20,21] with evidence of high fidelity at discrete beach sites in both Australia [17] and South Africa [16, 18]. Future MSP could benefit white sharks by conserving important prey resources, habitats and/or mitigating incidental catches [7,8,9]
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