Absence or avoidance? White shark response to killer whale predation risk

Abstract

Context: White sharks (Carcharodon carcharias) globally display seasonal site fidelity to coastal aggregations across their range, yet the prolonged absences from these aggregations have often been linked to the presence and predation by killer whales (Orcinus orca). This was the case following a predation event in 2015 at the Neptune Islands, when white sharks became abnormally absent for more than 2 months. However, how much this prolonged absence at the Neptune Islands was influenced by the predation event is unknown. Aims: Our study assessed whether the 69-day white shark absence in early 2015 was due to a predation event by killer whale in February 2015, or if such extended absence can reflect natural variations in residency at aggregations. Methods: We analysed 12 years (2013–2024) of white shark sighting records from wildlife tourism operators and acoustic telemetry data to investigate patterns of shark presence before and after the 2015 killer whale predation event, a shark mortality, and a killer whale sighting. Key results: White sharks exhibited six prolonged absences (mean absence duration + 3 standard deviations) across the 12-year study period, with the longest absence being 92 days, which was longer than the absence recorded in 2015 following killer whale predation (69 days). The number and extent of prolonged absences suggest that these departures are not unique to the 2015 event and may instead reflect natural or random variation in residency. Conclusions: Our findings showed that although killer whale predation and presence can trigger immediate responses and departure from aggregation sites, they are unlikely to be the sole driver of prolonged white shark absences at the Neptune Islands. Implications: Prolonged absences of white sharks may be influenced by killer whale predation as well as other predator–prey interactions and environmental factors. Integrative, long-term monitoring of all prey and predators is critical for understanding site fidelity and absence behaviour of white sharks.