The potential for vessel noise to mask biologically important sounds within ecologically significant embayments

• We estimated the distances for which auditory masking in sensitive marine life from vessel sound is expected.
• Source levels were 30 dB above the highest thresholds in cetaceans and fish.
• Vessel sound was estimated to have masking effect within several hundreds of metres.
• Vessels pose considerable concern for auditory masking in sensitive marine life.

With underwater sound levels rising due to increasing vessel activity, there is a pressing need to better understand the potential distances for which masking impacts on acoustically sensitive marine life may occur, especially in embayments with shipping activity. Given the known detrimental noise impacts on the marine environment, managing underwater noise pollution has been identified as a pressing conservation issue. Therefore, baseline underwater noise measurements from a range of vessels in the Hauraki Gulf Marine Park, a large and ecologically significant embayment (1.2 M Ha) in New Zealand, were undertaken and used to estimate detection distances for which potential auditory masking in dolphins, fish and crustaceans is expected. Sound pressure measurements and octave analyses of recorded vessel noise revealed considerable energy below 5 kHz at source levels of approximately 30 dB above the highest threshold in dolphins and fish. Measureable increases to background sound levels below 5 kHz of at least 54 ± 5.8 dB (mean ± SD) at the source were estimated to have a masking effect inside a minimum 90 m within the busy inner Gulf and 1240 m within the quieter outer Gulf. Impact zones increased considerably for dolphins with assumed detection thresholds equal to ambient sound pressures. These findings show that the sound emanating from both recreational and commercial vessels within the Hauraki Gulf will be significantly raising background sound levels and is likely to have a wide-ranging masking impact on marine life. These findings have significance for embayments worldwide for which vessel activity is a common feature.