Assessment of the impact of anthropogenic airborne noise on the behaviour of Cape fur seals during the breeding season in Namibia

Abstract

The increase of anthropogenic noise in the environment is a global phenomenon occurring in various types of habitats. Its impact on wildlife is therefore a growing research concern for many taxa. Due to their amphibious lifestyle, pinnipeds are exposed to anthropogenic noise in both aquatic and terrestrial environments. Using playback experiments, the present study assessed the impact of engine noise (car and boat) on the behaviour of Cape fur seals at the Pelican Point breeding colony, Namibia. Groups of individuals (35 groups, 369 individuals) were exposed either to low, medium or high amplitude levels of in-air noise, broadcast from the land or sea side. During the noise exposure, we found a significant increase in energetically costly behaviours: time spent awake, vigilance and locomotion for both females and pups. This was to the detriment of vital activities such as resting and nursing that decreased considerably (from 5.9 to 45% decrease) compared to the pre-playback phase without noise exposure. Animals' behavioural disturbance was limited to the 2-min period of noise exposure and we observed a rapid recovery when the noise ceased. We found stronger responses to boat motor noise broadcast from the sea side compared to car motor noise from land. Noise pollution from vehicles and boats in the vicinity of seal breeding colonies may threaten their health and the survival of their young by modifying their natural behaviour. It is therefore important to develop regulations for vehicles (speed, distance) in these areas with increasing tourist and recreational activities to limit disturbance.