Seals and shipping: quantifying population risk and individual exposure to vessel noise

Abstract

1. 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. 2. 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. 3. 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. 4. Predicted cumulative sound exposure level, cSELs(M pw ), over all seals was 176Á8 dB re 1 lPa 2 s (95% CI 163Á3-190Á4), ranging from 170Á2 dB re 1lPa 2 s (95% CI 168Á4-171Á9) to 189Á3 dB re 1 lPa 2 s (95% CI 172Á6-206Á0) for individuals. This represented an increase in 28Á3 dB re 1 lPa 2 s over measured ambient noise. For 20 of 28 animals in the study, 95% CI for cSELs(M pw ) had upper bounds above levels known to induce temporary threshold shift. Predictions of broadband received sound pressure levels were underestimated on average by 0Á7 dB re 1 lPa (AE3Á3). 5. 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. Details of electronic Supporting Information are provided below.Appendix S1. Usage maps.Appendix S2. Modelling acoustic exposure.Appendix S3. Sound exposure levels for individuals.Appendix S4. Validating acoustic predictions with underwater sound measurements.Appendix S5. Caveats and limitations.Appendix S6. Spatial co-occurrence using 2011 ship usage maps.

Understanding the population consequences of disturbance

“…We believe that evaluating the spatial and temporal overlap between a population's range and the distribution of stressors on the basis of density maps derived from the results of dedicated or historical surveys (Ellison et al., ; Hammond et al., ) should be a routine component of environmental impact assessments. Telemetry data can provide information on the patterns of repeated exposure for specific individuals (Costa et al., ; Falcone et al., ; Jones et al., ; Madsen et al., ; Pirotta, New, & Marcoux, ), and photographic identification (e.g., Calambokidis, Barlow, Ford, Chandler, & Douglas, ) can be used to estimate exposure risks for regularly monitored populations (Christiansen, Bertulli, Rasmussen, & Lusseau, ; Pirotta, Thompson, Cheney, Donovan, & Lusseau, ). In alternative, some studies examined the consequences of exposing all individuals in a population to the same amount of disturbance (Braithwaite, Meeuwig, & Hipsey, ; New et al., ; Villegas‐Amtmann, Schwarz, Gailey, Sychenko, & Costa, ; Villegas‐Amtmann, Schwarz, Sumich, & Costa, ).…”

“…Telemetry data can provide information on the patterns of repeated exposure for specific individuals (Costa et al, 2003;Falcone et al, 2017;Jones et al, 2017;Madsen et al, 2006;Pirotta, New, & Marcoux, 2018), and photographic identification (e.g., Calambokidis, Barlow, Ford, Chandler, & Douglas, 2009) can be used to estimate F I G U R E 1 The Population Consequences of Disturbance (PCoD) conceptual framework, modified from National Academies (2017). The boxes within the dashed gray boundary line represent the effects of exposure to a stressor and a range of ecological drivers on the vital rates of an individual animal.…”

The Effects of Ship Noise on Marine Mammals—A Review

“…Studies on the behavioral responses of pinnipeds to shipping noise have been undertaken at a range of spatial scales. A national-scale assessment of seals and shipping in the United Kingdom showed high rates of co-occurrence between gray seals or harbor seals and shipping traffic within 50 km of the coastline near haul-out sites (Jones et al, 2017). At regional and local scales, it was estimated, using sound propagation models, that harbor seals in the Moray Firth were exposed to 24-h cumulative SEL 3 between 170 dB re 1 µPa 2 s (95% CI 168-172) and 189 dB re 1 µPa 2 s (95% CI 173-206) from shipping (Jones et al, 2017).…”

“…A national-scale assessment of seals and shipping in the United Kingdom showed high rates of co-occurrence between gray seals or harbor seals and shipping traffic within 50 km of the coastline near haul-out sites (Jones et al, 2017). At regional and local scales, it was estimated, using sound propagation models, that harbor seals in the Moray Firth were exposed to 24-h cumulative SEL 3 between 170 dB re 1 µPa 2 s (95% CI 168-172) and 189 dB re 1 µPa 2 s (95% CI 173-206) from shipping (Jones et al, 2017). When considering the upper limits of the 95% confidence intervals, these predicted values exceeded the estimated thresholds for the onset of TTS (Southall et al, 2007(Southall et al, , 2019.…”

Age–length relationships in UK harbour seals during a period of population decline

“…Thus, although these recent abundance data suggest this trend is continuing for some populations, others, such as those in the West Scotland and the Western Isles MUs, have been stable or increasing over the same time period (SCOS, 2017). The reasons for these declines are not clear, but potential factors include increased competition for food by sympatric grey seals (Halichoerus grypus) and other top piscivorous predators, changes in prey availability or prey quality, increased predation (Brownlow, Onoufriou, Bishop, Davison, & Thompson, 2016), interactions with vessels (Jones et al, 2017), and exposure to biotoxins produced by harmful algae (Hall & Frame, 2010).…”