Sharks often modify their behaviour to obtain food from humans. Food provisioning can lead to behavioural conditioning, which can alter resource use patterns and interactions within and between species. We used acoustic telemetry and dietary biomarkers (fatty acids and stable isotopes) to quantify dusky (Carcharhinus obscurus; n = 18) and Galapagos (C. galapagensis; n = 16) shark associations with fishing piers at Norfolk Island, Australia between 2021 and 2024. Individuals visited the piers, on average, once every four days (~ 3 h daily), with dusky sharks usually arriving in the early afternoon and staying until dusk while Galapagos sharks arrived at dusk and left in the early morning. Despite this temporal partitioning, the diets of both species were indistinguishable from each other and showed only limited contribution of discarded fish; however, fish scraps were more common in the diet of sharks with high residency to the piers. These findings indicate that although incidental feeding contributes to the presence of sharks at the piers, it has likely not markedly altered natural foraging behaviour with regular visits to the piers only conducted intermittently by a subset of the tagged population to supplement diet. Understanding how sharks use the piers in response to human activities will help assess current waste disposal practices at Norfolk Island and ongoing monitoring needs.
Matley et al. (Thu,) studied this question.