Environmental predictive models for shark attacks in Australian waters

Shark attacks are rare but traumatic events that generate social and economic costs and often lead to calls for enhanced attack mitigation strategies that are detrimental to sharks and other wildlife. Improved understanding of the influence of environmental conditions on shark attack risk may help to inform shark management strategies. Here, we developed predictive models for the risk of attack by white Carcharodon carcharias, tiger Galeocerdo cuvier, and bull/ whaler Carcharhinus spp. sharks in Australian waters based on location, sea surface temperature (SST), rainfall, and distance to river mouth. A generalised additive model analysis was performed using shark attack data and randomly generated pseudo-absence non-attack data. White shark attack risk was significantly higher in warmer SSTs, increased closer to a river mouth (<10 km), and peaked at a mean monthly rainfall of 100 mm. Whaler shark attack risk increased significantly within 1 km of a river mouth and peaked in the summer months. Tiger shark attack risk increased significantly with rainfall. We performed additional temporal and spatio-temporal analyses to test the hypothesis that SST anomaly (SST_anom) influences white shark attack risk, and found that attacks tend to occur at locations where there is a lower SST_anom (i.e. the water is relatively cooler) compared to surrounding areas. On the far north coast of eastern Australia — an attack hotspot — a strengthening of the East Australian Current may cause white sharks to move into cooler upwelling waters close to this stretch of the coast and increase the risk of an attack.