A multidisciplinary approach to assess the impacts of anthropogenic noise on Australian fur seals (Arctocephalus pusillus doriferus)

Abstract

Vessel traffic is the greatest contributor to marine anthropogenic noise pollution, and particularly affects species in coastal areas. Seal Rocks (Victoria), the largest Australian fur seal (Arctocephalus pusillus doriferus) breeding colony, has the smallest vessel exclusion zone during pupping and breeding for the species, coinciding with the highest vessel traffic. The overall aim of this thesis was to determine the impact of vessel noise at Seal Rocks by testing the behavioural response of seals to vessel noise, and to assess their risk of disturbance at different times of year through evaluation of pup health, stress, and exposure to vessel visitation. Controlled noise exposure experiments were conducted from January to April (peak vessel visitation) and May to August (off-peak vessel visitation) in 2022 and 2023. High level noise (76-80 dB) resulted in increased vigilance and interruption to vital behaviours for the duration of noise exposure in both peak and off-peak periods. Pups were sampled in late December (2021, 2022) at 3-6 weeks of age (peak), and in May (2022, 2023) at 5-6 months of age (off-peak). Significant differences in haematological parameters and stress hormone concentrations in pup fur between peak and off-peak periods highlighted the increased vulnerability of both mothers and pups when human visitation highest. Finally, passive acoustic monitoring and direct visual observations were used to monitor vessel visitation between peak and off-peak periods. Visual observations were also used to assess compliance with approach regulations. Vessel visitation and the associated noise was significantly higher in the peak season, and 32% of vessels were in breach of approach regulations. Results can be applied to future evaluations of management regulations at Seal Rocks and other pinniped breeding colonies, and support the need for enhanced protection from potential anthropogenic disturbance during pupping, breeding, and the early neonatal period.