Distribution of Reported Impulsive Sounds in the Sea

Human activities introduce many types of energy into the marine environment including sound, light and other electromagnetic fields, heat and radioactive energy. Of these, the most widespread and pervasive is underwater sound. It is likely that the amount of underwater sound has been increasing since the advent of steam driven ships although there have been very few studies to quantify any such increase in the OSPAR Maritime Area.

Anthropogenic sound is commonly known as noise, but for the purposes of this assessment the term ‘noise’ is used only in relation to sound that has the potential to cause negative impacts on marine life. The term ‘sound’ is used to refer to the acoustic energy radiated from a vibrating object, with no particular reference to its function or potential effect. ‘Sounds’ include both meaningful signals and ‘noise’ which may have either no particular impact or may have a range of adverse effects. The term ‘noise’ is only used where adverse effects are specifically described, or when referring to specific technical distinctions such as ‘masking noise’ and ‘ambient noise’. (Van der Graaf et al., 2012).

Sound sources can be categorised as continuous or impulsive. Impulsive sounds are of short duration and with a rapid onset (e.g. explosions, pile driving, seismic airguns, sonar), while continuous sounds are long lasting and do not have pulse characteristics (e.g. shipping, dredging). Impulsive sounds may be repeated at intervals (e.g. pile driving), and at distance will become diffused and may have a more continuous nature. High frequency sounds propagate less well in the marine environment than low frequency sounds, which can travel far in waters that are sufficiently deep.

Marine organisms that are exposed to anthropogenic sound (e.g. harbour porpoise Phocoena phocoena, see Figure a; and European seabass, Dicentrarchus labrax; see Figure b) can be adversely affected over short timescales (acute effect) and over longer periods. Adverse effects may be subtle (e.g. temporary reduction in hearing sensitivity, physiological stress) or obvious (e.g. overt behavioural responses, death). While there is a growing body of literature on the potential effects of anthropogenic sound on individual animals (Williams et al., 2015), obtaining direct observations of the effects of anthropogenic sound on particular ecosystems or populations is challenging. As such, there is uncertainty over whether and how effects on individuals are translated to the population or ecosystem scale.

Descriptor 11 of the EU Marine Strategy Framework Directive (2008/56/EC) contains two Criteria of Good Environmental Status (GES) in European waters: D11C1 on “Anthropogenic impulsive sound in water” and D11C2 on “Anthropogenic continuous low-frequency sound in water”. At present, there are no quantitative targets for GES, although these are expected to be defined since the Directive requires that “Member States shall establish threshold values for these levels through cooperation at Union level, taking into account regional or subregional specificities.” OSPAR has adopted Criterion D11C1 as an OSPAR Common Indicator, which is the subject of this assessment. This Common Indicator considers the pressure from impulsive noise (a second Common Indicator to assess the risk of impact is in preparation). The indicator is based on the spatio-temporal distribution of low-frequency and mid-frequency impulsive sound sources within the OSPAR Maritime Area.

Data were obtained from the Impulsive Noise Registry, which was developed for OSPAR by ICES, in 2016, to hold data on activities that generate impulsive sound. The registry accords with the guidelines from the EU Technical Group on Underwater Noise (adopted by OSPAR in 2014; OSPAR Agreement 2014-08 ), and is maintained by ICES. Initially, this registry was supported by OSPAR alone, but is now also used by HELCOM and may be used by other Regional Seas Conventions in the future. Data have been uploaded for several countries and this process is expected to continue. The database collates the data in a standard format and in accordance with the data requirements for the OSPAR Impulsive Noise Indicator (OSPAR, 2014).

This assessment uses data from 2015-2017 (see Table a for a summary of the activity types each country reported for this period).

The OSPAR Impulsive Noise Indicator is defined as follows:

Distribution in time and place of loud, low and mid frequency impulsive sounds – proportion of days and their distribution within a calendar year over areas of a determined surface, as well as their spatial distribution, in which anthropogenic sound sources exceed levels that are likely to entail significant impact on marine animals measured as Sound Exposure Level [SEL] (in dB re 1µPa2.s) or as peak Sound Pressure Level [SPLpeak] (in dB re 1 µPa peak) at one metre, measured over the frequency band 10 Hz to 10kHz. (OSPAR, 2014)

In other words, the Indicator records the number of days within a specified spatial unit in which anthropogenic impulsive sound occurred in a given calendar year. Only sound sources above a specified intensity level are included. These levels are detailed in the technical specification of the Impulsive Noise Indicator (OSPAR, 2014). The spatio-temporal unit used in the assessment is termed Pulse Block Day. The spatial component of the Pulse Block Day is the ICES statistical sub-rectangle (hereafter ICES sub-block), which is defined in a standard way throughout the OSPAR Maritime Area, and provides detailed resolution at the regional scale.

Issues encountered with spatial units

Several different spatial units are used by Contracting Parties to record impulsive sound activity. In some cases, point source data are provided, giving an unambiguous location for the activity, which can then be readily attributed to an ICES sub-block for the purposes of the assessment. In other cases, activities are licensed within a specified area (e.g. UK oil and gas licensing blocks), and data are provided as polygons within which activity occurred. Polygon data presented a logistical challenge for this assessment because they do not align with ICES sub-blocks and some Contracting Parties use differently sized polygons for different activities. For the purposes of this assessment, the ICES sub-block which contained the centroid of the reported polygon was allotted the Pulse Block Day for that block (see Figure c). This contrasts with the previous assessment (Intermediate Assessment 2017), in which all ICES sub-blocks which overlapped with a given polygon of activity were considered to contain the Pulse Block Days allotted to that polygon. This resulted in a substantial over-estimation of spatial coverage, because even slight overlap with an adjacent ICES sub-block resulted in the activity being recorded throughout that block.  The current approach reduces the overestimation in pressure footprint (e.g. from 180% to 120% of reported area in 2015), although in some cases up to 33% of the area of reported activity may be assigned to the adjacent block. Hence, if an activity (or part of) had occurred in that area, then the allotted sub-block would not cover its original location. This does not change the total PBD spatial and temporal coverage. The original reported data is retained in the registry, which allows further methodological refinements to be made in future.

This assessment uses the Impulsive Noise Registry to assess the OSPAR Impulsive Noise Indicator, using data available from the first three years of reporting (2015-2017). Only partial data were provided by each of the contributing Contracting Parties (Belgium, Denmark, France, Germany, Ireland, the Netherlands, Sweden and the UK), so the assessment cannot be considered comprehensive. In 2015, the pressure from seismic surveys covered large contiguous areas of pulse blocks in the Northern and Eastern North Sea and the North-eastern Atlantic, but this has diminished in 2016 and 2017. Pressure from explosions and pile driving activity was scattered throughout the Southern North Sea, with reported pile driving activity highest in 2016, and explosions highest in 2017. Reported sonar activity was mostly in the Western English Channel and Southern Celtic Seas, with limited activity reported in the North Sea and Atlantic. More complete reporting in future years should enable a more comprehensive assessment of activity, which will inform Contracting Parties of activity levels at a regional scale. This will include spatio-temporal trends in the distribution and intensity of activity.

This assessment is pressure-based and describes the distribution of impulsive sound sources in the OSPAR Maritime Area. The use of Pulse Block Days provides a link between the activity reported in the Impulsive Noise Registry and the maps produced for this assessment. The assessment highlights the locations of sources around which marine animals could potentially have been affected during 2015-2017, although the occurrence of effects will also depend on the distribution of marine organisms and their susceptibility to sound exposure. The likelihood and consequences of effects on marine organisms arising from exposure to impulsive sounds are not assessed in this assessment. Work to develop further Indicators to assess the risk of impact from these sound sources on marine species is planned.

Dekeling, R.P.A., Tasker, M.L., Van der Graaf, A.J., Ainslie, M.A, Andersson, M.H., André, M., Borsani, J.F., Brensing, K., Castellote, M., Cronin, D., Dalen, J., Folegot, T., Leaper, R., Pajala, J., Redman, P., Robinson, S.P., Sigray, P., Sutton, G., Thomsen, F., Werner, S., Wittekind, D., Young, J.V., Monitoring Guidance for Underwater Noise in European Seas, JRC Scientific and Policy Report EUR 26555 EN, Publications Office of the European Union, Luxembourg, 2014, doi: 10.2788/27158

OSPAR (2014) Summary record of the meeting of the Environmental Impacts of Human Activities Committee (EIHA). EIHA 14/10/1-E

Van der Graaf AJ, Ainslie MA, André M, Brensing K, Dalen J, Dekeling RPA, Robinson S, Tasker ML, Thomsen F, Werner S (2012). European Marine Strategy Framework Directive - Good Environmental Status (MSFD GES): Report of the Technical Subgroup on Underwater noise and other forms of energy

Williams, R, et al. (2015) Impacts of anthropogenic noise on marine life: Publication patterns, new discoveries, and future directions in research and management. Ocean & Coastal Management 115, 17-24.