Abstract
Recreational boating is an increasing activity in coastal areas and its spatiotemporal overlap with key habitats of marine species pose a risk for negative noise impacts. Yet, recreational vessels are currently unaccounted for in vessel noise models using Automatic Identification System (AIS) data. Here we conduct a case study investigating noise contributions from vessels with and without AIS (non-AIS) in a shallow coastal area within the Inner Danish waters. By tracking vessels with theodolite and AIS, while recording ambient noise levels, we find that non-AIS vessels have a higher occurrence (83%) than AIS vessels, and that motorised recreational vessels can elevate third-octave band noise centred at 0.125, 2 and 16 kHz by 47–51 dB. Accordingly, these vessels dominated the soundscape in the study site due to their high numbers, high speeds and proximity to the coast. Furthermore, recreational vessels caused 49–85% of noise events potentially eliciting behavioural responses in harbour porpoises (AIS vessels caused 5–24%). We therefore conclude that AIS data would poorly predict vessel noise pollution and its impacts in this and other similar marine environments. We suggest to improve vessel noise models and impact assessments by requiring that faster and more powerful recreational vessels carry AIS-transmitters.
Highlights
Motorised vessels are the most widespread source of anthropogenic underwater noise and may be causing behavioural responses and acoustic masking in a wide range of marine species worldwide[1,2,3]
We have shown that recreational vessels without Automatic Identification System (AIS) transmitters were the most frequent vessels and the dominant contributors of underwater noise in a shallow, coastal area
While acoustic modelling is undoubtedly a valuable tool for predicting vessel noise, in particular in offshore deep-water areas, we conclude that modelling on the basis of AIS data alone may lead to severe underestimations of the actual vessel noise levels and noise impacts in shallow coastal waters with dense recreational boating
Summary
Motorised vessels are the most widespread source of anthropogenic underwater noise and may be causing behavioural responses and acoustic masking in a wide range of marine species worldwide[1,2,3]. The more than 30 million recreational vessels worldwide[12] are not required to have an AIS, and these non-AIS vessels are currently not accounted for in AIS-based models[13,14] This is despite that recreational vessels may emit considerable levels of broadband noise[15,16] with potential negative effects on marine species with a wide range of hearing capabilities[17], including fish[18,19], crustaceans[20], sea turtles[21] and cetaceans[14,16,22]. Low-frequency noise from large distant vessels may be less of a concern in shallow waters, whereas mid-to-high frequency noise from closer sources, such as small recreational vessels without AIS, may contribute significant to local soundscapes with potential negative effects on marine species that depend on these habitats to forage, breed and/or rest[18,20,21,32]. High speeds and broadband noise emissions of motorised non-AIS vessels, we find that recreational vessels were the main contributors of noise exceeding response thresholds of porpoises
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