Environmental and anthropogenic factors affecting the increasing occurrence of shark-human interactions around a fast-developing Indian Ocean island

Erwann Lagabrielle,Nicolas Loiseau,Agathe Allibert,James P. Kilfoil,Anne Lemahieu,Jeremy J. Kiszka

doi:10.1038/s41598-018-21553-0

Abstract

Understanding the environmental drivers of interactions between predators and humans is critical for public safety and management purposes. In the marine environment, this issue is exemplified by shark-human interactions. The annual shark bite incidence rate (SBIR) in La Réunion (Indian Ocean) is among the highest in the world (up to 1 event per 24,000 hours of surfing) and has experienced a 23-fold increase over the 2005–2016 period. Since 1988, 86% of shark bite events on surfers involved ocean-users off the leeward coast, where 96% of surfing activities took place. We modeled the SBIR as a function of environmental variables, including benthic substrate, sea temperature and period of day. The SBIR peaked in winter, during the afternoon and dramatically increased on coral substrate since the mid-2000s. Seasonal patterns of increasing SBIR followed similar fluctuations of large coastal shark occurrences (particularly the bull shark Carcharhinus leucas), consistent with the hypothesis that higher shark presence may result in an increasing likelihood of shark bite events. Potential contributing factors and adaptation of ocean-users to the increasing shark bite hazard are discussed. This interdisciplinary research contributes to a better understanding of shark-human interactions. The modeling method is relevant for wildlife hazard management in general.

Highlights

Understanding the environmental drivers of interactions between predators and humans is critical for public safety and management purposes
Of the 51 shark-human interactions (SHI) recorded during the study period (1980–2016), 43 shark bite events fitted the criteria for inclusion in the study (Fig. 2)
Over the 1980–2016 period, La Réunion was in the top-6 list of global hotspots for unprovoked shark bites reported in a single administrative unit

Summary

Introduction

Understanding the environmental drivers of interactions between predators and humans is critical for public safety and management purposes. Potential contributing factors and adaptation of ocean-users to the increasing shark bite hazard are discussed This interdisciplinary research contributes to a better understanding of shark-human interactions. Over the past three decades, the number of unprovoked shark bites on humans has increased around the world, creating numerous challenges for coastal management policies[4]. This increasing trend has been documented in multiple countries[5], and has been anecdotally linked to increasing recreational activities[6], surfing[5,7,8]. Trends in shark bite incidence rate (SBIR) can be used to explore links between environmental variables and risks of human-shark interactions[8,17]. The number of studies using this approach remains rare, perhaps due to the lack of ocean-user and environmental monitoring data over the same spatial and temporal scales[17,26,27]

Methods

Results

Conclusion