Abstract
Summary Vessels can have acute and chronic impacts on marine species. The rate of increase in commercial shipping is accelerating, and there is a need to quantify and potentially manage the risk of these impacts. Usage maps characterising densities of grey and harbour seals and ships around the British Isles were used to produce risk maps of seal co‐occurrence with shipping traffic. Acoustic exposure to individual harbour seals was modelled in a study area using contemporaneous movement data from 28 animals fitted with UHF global positioning satellite telemetry tags and automatic identification system data from all ships during 2014 and 2015. Data from four acoustic recorders were used to validate sound exposure predictions. Across the British Isles, rates of co‐occurrence were highest within 50 km of the coast, close to seal haul‐outs. Areas identified with high risk of exposure included 11 Special Areas of Conservation (SAC; from a possible 25). Risk to harbour seal populations was highest, affecting half of all SACs associated with the species. Predicted cumulative sound exposure level, cSELs(Mpw), over all seals was 176·8 dB re 1 μPa2 s (95% CI 163·3–190·4), ranging from 170·2 dB re 1μPa2 s (95% CI 168·4–171·9) to 189·3 dB re 1 μPa2 s (95% CI 172·6–206·0) for individuals. This represented an increase in 28·3 dB re 1 μPa2 s over measured ambient noise. For 20 of 28 animals in the study, 95% CI for cSELs(Mpw) had upper bounds above levels known to induce temporary threshold shift. Predictions of broadband received sound pressure levels were underestimated on average by 0·7 dB re 1 μPa (±3·3). Synthesis and applications. We present a framework to allow shipping noise, an important marine anthropogenic stressor, to be explicitly incorporated into spatial planning. Potentially sensitive areas are identified through quantifying risk to marine species of exposure to shipping traffic, and individual noise exposure is predicted with associated uncertainty in an area with varying rates of co‐occurrence. The detailed approach taken here facilitates spatial planning with regard to underwater noise within areas protected through the Habitats Directive, and could be used to provide evidence for further designations. This framework may have utility in assessing whether underwater noise levels are at Good Environmental Status under the Marine Strategy Framework Directive.
Highlights
Major shipping routes converge around populated coastlines with relatively high densities of ships accessing ports.Coastal regions serve as important habitats for many species of marine mammals leading to the potential for interactions with ships in these areas
Acoustic exposure to individual harbour seals was modelled in a study area using contemporaneous movement data from 28 animals fitted with UHF global positioning satellite telemetry tags and automatic identification system data from all ships during 2014 and 2015
There is a perceived requirement for effective spatial planning where shipping traffic and marine mammals share the same environment (Erbe et al 2014; Williams et al 2015), but the level of management required will depend to a large extent on the scale and intensity of interactions and the effects these have on the behaviour and welfare of the species of interest
Summary
Coastal regions serve as important habitats (e.g. for breeding, foraging) for many species of marine mammals leading to the potential for interactions with ships in these areas. Marine mammal habitats are often conserved through protected areas or other spatial planning measures. There is a perceived requirement for effective spatial planning where shipping traffic and marine mammals share the same environment (Erbe et al 2014; Williams et al 2015), but the level of management required will depend to a large extent on the scale and intensity of interactions and the effects these have on the behaviour and welfare of the species of interest. Difficulties in observing these unpredictable events mean that mortality rates are still poorly understood
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