Assessing the short-term impacts of in-air firework sounds on marine species in Cape Town, South Africa

Animals can adapt to anthropogenic sound, however, sudden impulsive sounds, such as fireworks, can trigger behavioural responses. The Victoria and Alfred Waterfront, South Africa, holds several threatened and endangered coastal marine species and hosts an annual New Year's Eve celebration involving firework displays. Video and acoustic data were collected during this event to assess the short-term impacts of in-air firework sounds on common and accessible species, Hartlaub's gulls Chroicocephalus hartlaubii and Cape fur seals Arctocephalus pusillus pusillus. The propagation of firework pulses underwater was also assessed in the harbour. Both species increased vocal production soon after firework cessation, and the seals shifted from sleeping to increased vigilance and locomotion at exposure onset. The in-air frequency of firework sounds overlapped the communicative frequency band of both species, resulting in potential acoustic masking or disruption. Underwater, the received sound pressure level of fireworks was ~ 143 dB re 1 µPa, providing evidence of in-air firework sound propagation underwater. However, this contributed very little to the underwater soundscape. This case study provides baseline information on the short-term impacts of fireworks on marine species. Such displays that cause disturbance likely constitute harassment of threatened or protected marine species, prohibited under South African law.