Shark Spotters: Successfully reducing spatial overlap between white sharks (Carcharodon carcharias) and recreational water users in False Bay, South Africa.

Sarah Waries,Tamlyn Engelbrecht,Alison Kock,Heather M Patterson,M Justin O’Riain

doi:10.1371/journal.pone.0185335

Abstract

White sharks (Carcharodon carcharias) are apex predators that play an important role in the structure and stability of marine ecosystems. Despite their ecological importance and protected status, white sharks are still subject to lethal control to reduce the risk of shark bites for recreational water users. The Shark Spotters program, pioneered in Cape Town, South Africa, provides a non-lethal alternative for reducing the risk of human-shark conflict. In this study we assessed the efficacy of the Shark Spotters program in reducing overlap between water users and white sharks at two popular beaches in False Bay, South Africa. We investigated seasonal and diel patterns in water use and shark presence at each beach, and thereafter quantified the impact of different shark warnings from shark spotters on water user abundance. We also assessed the impact of a fatal shark incident on patterns of water use. Our results revealed striking diel and seasonal overlap between white sharks and water users at both beaches. Despite this, there was a low rate of shark-human incidents (0.5/annum) which we attribute partly to the success of the Shark Spotters program. Shark spotters use visual (coloured flags) and auditory (siren) cues to inform water users of risk associated with white shark presence in the surf zone. Our results showed that the highest risk category (denoted by a white flag and accompanying siren) caused a significant reduction in water user abundance; however the secondary risk category (denoted by a red flag with no siren) had no significant effect on water users. A fatal shark incident was shown to negatively impact the number of water users present for at least three months following the incident. Our results indicate that the Shark Spotters program effectively reduces spatial overlap between white sharks and water users when the risk of conflict is highest.

Highlights

Human-wildlife conflict presents one of the greatest challenges to the effective conservation of wildlife species [1,2,3,4]
This finding is supported by data from acoustic telemetry [29], which showed a marked absence of white sharks along the inshore areas of False Bay during the winter months, a time of year when white sharks typically aggregate at Seal Island in order to predate on young of the year Cape fur seals [29,30,31]
It is imperative that the efficacy of the Shark Spotters program be maximised to prevent conflict during these times of year when overlap between water users and white sharks peaks in the inshore zone

Summary

Introduction

Human-wildlife conflict presents one of the greatest challenges to the effective conservation of wildlife species [1,2,3,4]. A number of areas with sustained high levels of shark attacks have implemented lethal control strategies to lower the risk of human-shark conflict and restore public confidence in beach safety. These measures are varied, and range from short-term shark hunts and culls, to long-term control methods, including the use of permanently or semi-permanently deployed fishing gear such as large-mesh gill nets and/or baited “drum lines” [17]. Long-term shark control programs, such as those currently implemented at a number of popular beaches in Queensland and New South Wales in Australia, and in KwaZulu Natal, South Africa, have been shown to successfully reduce the number of shark incidents in these areas [23,24,25]. Alternative, non-lethal strategies that can be implemented on a long-term basis are needed to mitigate conflict between water users and sharks

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Results

Discussion

Conclusion