Abstract
The potential impacts of underwater noise on marine mammals are widely recognised, but uncertainty over variability in baseline noise levels often constrains efforts to manage these impacts. This paper characterises natural and anthropogenic contributors to underwater noise at two sites in the Moray Firth Special Area of Conservation, an important marine mammal habitat that may be exposed to increased shipping activity from proposed offshore energy developments. We aimed to establish a pre-development baseline, and to develop ship noise monitoring methods using Automatic Identification System (AIS) and time-lapse video to record trends in noise levels and shipping activity. Our results detail the noise levels currently experienced by a locally protected bottlenose dolphin population, explore the relationship between broadband sound exposure levels and the indicators proposed in response to the EU Marine Strategy Framework Directive, and provide a ship noise assessment toolkit which can be applied in other coastal marine environments.
Highlights
Acoustic measurements in the Northeast Pacific indicate that underwater noise levels in the open ocean have been rising for at least the last five decades due to increases in shipping (Andrew et al, 2002; McDonald et al, 2006; Chapman and Price, 2011) correlated to global economic growth (Frisk, 2012)
The 62% of peaks identified was composed of 52% attributed to vessel closest point of approach (CPA), with the remaining 10% due to other vessel movements which were clearly distinct from CPAs, such as acceleration from or deceleration to stationary positions
The measurements of underwater noise at The Sutors and Chanonry establish baseline noise levels within the Moray Firth Special Area of Conservation (SAC) during the summer field season, providing an important benchmark against which to quantify the acoustic impact of any future changes in shipping activity or other anthropogenic sources
Summary
Acoustic measurements in the Northeast Pacific indicate that underwater noise levels in the open ocean have been rising for at least the last five decades due to increases in shipping (Andrew et al, 2002; McDonald et al, 2006; Chapman and Price, 2011) correlated to global economic growth (Frisk, 2012). Escalations in human activity, including shipping, pile-driving and seismic surveys, have transformed coastal marine soundscapes (Richardson et al, 1995; Hildebrand, 2009) with uncertain consequences for the ecosystems that inhabit them. These large-scale changes in the acoustic environment are of particular concern for marine mammals (Tyack, 2008), which rely on sound as their primary sensory mode.
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