White shark behaviour altered by stranded whale carcasses: Insights from drones and implications for beach management

• Published in: Ocean & coastal management 2021-02, Vol.200, p.105477, Article 105477
• Main Authors: Tucker, James P., Colefax, Andrew P., Santos, Isaac R., Kelaher, Brendan P., Pagendam, Daniel E., Butcher, Paul A.
• Format: Article
• Language: English
• Subjects: abundance; bay; Carcharodon carcharias; Drone; dynamics; Elasmobranch; Oceanografi, hydrologi och vattenresurser; Oceanography; Oceanography, Hydrology and Water Resources; patterns; Remotely piloted aircraft; Remotely piloted aircraft system (RPAS); system (RPAS); unmanned aerial vehicles; Water Resources; Whale carcass
• ISSN: 0964-5691; 1873-524X
• DOI: 10.1016/j.ocecoaman.2020.105477

White sharks (Carcharodon carcharias) are attracted to and scavenge on floating whale carcasses. However, little is known about how stranded whale carcasses may affect their behaviour. With increasing whale populations and beach stranding events, sharks may be attracted to nearshore waters at carcass sites, increasing the potential conflict with human use. Here, we used aerial drones to assess whether white shark behaviour around stranded whale carcasses differs from their behaviour away from carcasses. We quantified white shark behaviour by measuring swim speed, net velocity, straightness and sinuosity of shark tracks, as well as the total length of each shark. White sharks in the vicinity of whale carcasses travelled at 0.46 m s−1 (±0.06 SD) faster, were 0.26 m (±0.15 SD) longer, swam tracks that were 0.15 (±0.11 SD) lower on the straightness index, and showed more sinuous tracks by 0.07 (±0.02 SD), compared to sharks away from a carcass. The presence of a stranded whale carcass may, therefore, significantly altered the behaviour and size of white sharks close to shore. As white shark activity increases in a relatively small nearshore area, which was indicated by decreased straightness and increased sinuosity, there may be an elevated risk of shark interactions with water users in the vicinity of stranded whale carcasses. [Display omitted] •Drone were used to observe the behaviour of white sharks in the presence of stranded whale carcasses.•White shark behaviour is altered significantly by the presence of a stranded whale carcass.•White sharks move faster, were longer (total length), swam less straight, and their tracks were more sinuous.•Observed changes in white shark behaviour may present an increased risk to water users.•Changes in shark behaviour should be considered when managing whale carcass stranding events.