Harbour seals avoid tidal turbine noise: implications for collision risk

1. Tidal stream energy converters (turbines) are currently being installed in tidally energetic coastal sites. However, there is currently a high level of uncertainty surrounding the potential environmental impacts on marine mammals. This is a key consenting risk to commercial introduction of tidal energy technology. Concerns derive primarily from the potential for injury to marine mammals through collisions with moving components of turbines. To understand the nature of this risk, information on how animals respond to tidal turbines is urgently required. 2. We measured the behaviour of harbour seals in response to acoustic playbacks of simulated tidal turbine sound within a narrow coastal channel subject to strong, tidally induced currents. This was carried out using data from animal-borne GPS tags and shore-based observations, which were analysed to quantify behavioural responses to the turbine sound. 3. Results showed that the playback state (silent control or turbine signal) was not a significant predictor of the overall number of seals sighted within the channel. 4. However, there was a localised impact of the turbine signal; tagged harbour seals exhibited significant spatial avoidance of the sound which resulted in a reduction in the usage by seals of between 11 and 41% at the playback location. The significant decline in usage extended to 500 m from the playback location at which usage decreased by between 1 and 9% during playback. Synthesis and applications: This study provides important information for policy makers looking to assess the potential impacts of tidal turbines and advise on development of the tidal energy industry. Results showing that seals avoid tidal turbine sound suggest that a proportion of seals encountering tidal turbines will exhibit behavioural responses resulting in avoidance of physical injury; in practice, the empirical changes in usage can be used directly as avoidance rates when using collision risk models to predict the effects of tidal turbines on seals. There is now a clear need to measure how marine mammals behave in response to actual operating tidal turbines in the long term to learn whether marine mammals and tidal turbines can co-exist safely at the scales currently envisaged for the industry

Dynamic habitat corridors for marine mammals: intensive use of a coastal channel by harbour seals is modulated by tidal currents [abstract]

Dynamic habitat corridors for marine mammals: intensive use of a coastal channel by harbour seals is modulated by tidal currents [abstract

Exploring influences of lower-frequency acoustic deterrent devices (ADDs) on harbour porpoise in Scottish coastal waters [Abstract]

Conference abstrac

Variation in ambient noise levels and acoustic propagation across a tidal flow [abstract]

Variation in ambient noise levels and acoustic propagation across a tidal flow [abstract

STIMweighted_J11_1hour_withRamp

Sound file (.wav) used during playbacks of simulated tidal turbine sound to harbour seals to investigate avoidance responses. The file has a 10 second ramp at the start and end of the file, and is frequency weighted for use with a J11 underwater speaker

JApEcol_Hastie_etal_observation_data_Dryad

Land based observer data (.xlsx) used in the analysis of seal responses to tidal turbine sounds. This is effectively counts of seals observed in the water during acoustic playbacks of tidal turbine sound and silent controls. Data were collected by a series of observers located on a clifftop overlooking the study area (Kyle Rhea, Isle of Skye, Scotland) README file is provided as a tab in the file

JApEcol_Hastie_etal_seal_telemetry_data_Dryad

Harbour seal telemetry data (.xlsx) used in the analysis of changes in usage with distance from the location of playbacks of tidal turbine sound. The data are regularised lat-lon locations from 10 individual harbour seals tagged with GPS telemetry devices. README is provided as a tab in the file

Sediment transport and the freshwater modification of tidal hydraulics approaching a fjordic sill: The Falls of Lora, Loch Etive, western Scotland, UK

The Falls of Lora (FoL), Loch Etive, illustrates a highly energetic tidal site across a shallow (mean depth = 8 m) fjordic sill. The FoL hydrodynamics have been investigated using an acoustic Doppler current profiler (ADCP), a numerical flow model, water‐level data and meteorological data. Additionally, four bathymetric timeseries datasets (from February 2014, September 2020, November 2021 and June 2022) provided alternative indication of flow variability by monitoring the geometry of submarine sediment bedforms. A correlation of 0.22 (−0.2 < 97.5% confidence interval < 0.2) was found between catchment‐integrated precipitation and residual water height (with effects of tide and atmospheric pressure removed). Residual water height varied by 0.77 m. Artificially increasing the water height by up to 0.6 m at the model's up‐fjord open boundary to emulate the effects of precipitation increased (decreased) peak depth‐averaged flow speed of the ebb (flood) jet by 0.44 m/s (0.34 m/s) whilst modifying residual flow fields around the FoL. The freshwater‐modified residual flow correlated with the westward displacement of a flow transverse sediment ridge observed in two bathymetric surveys conducted after periods of relatively high precipitation. Additionally, in one of the surveys associated with increased precipitation, wavelength stretching in the sediment dunes was observed uniquely at the western approach to the FoL, dominated by the freshwater‐enhanced ebb flow. Increasing the water levels of the up‐fjord boundary from 0.1 to 0.6 m resulted in an increased mean bedload transport of 2.28 × 10−5 m3/s (370% increase) for these dunes dominated by the ebb current. Whereas Loch Etive has an anomalously high freshwater influence on sill flow compared with other Scottish fjords, it is predicted that freshwater inputs are a significant influence on sill hydrodynamics and nearby sediment transport pathways in other fjordic systems.</p

DataSheet1_Monitoring cetacean occurrence and variability in ambient sound in Scottish offshore waters.docx

The characterisation of marine soundscapes allows observation of spatiotemporal distribution of vocalising species and human activities, which can inform an assessment of their interactions. Such data are important for monitoring the ecological status of marine habitats. The Scottish Atlantic Frontier is an important habitat for a variety of cetacean species. Historic whaling has heavily impacted several species inhabiting these waters and current comprehensive information about seasonal occurrence and distribution is lacking for all species. This study presents year-round passive acoustic monitoring data from ten sites in this understudied region. The three most offshore sites were examined for baleen whale vocalisations, and four species were regularly detected. Fin whale detections peaked from October to January and were at their lowest during May and June. Humpback whale song was detected as early as January but showed a strong seasonal peak in March and April. In contrast, minke whales were detected regularly throughout the year but with a peak in detections from October to November, when sei whales were also detected. All monitoring sites showed frequent occurrence of odontocete echolocation clicks and whistles. Comprised mainly of delphinid vocalisations, whistles and clicks were detected on an almost-daily basis among the offshore sites, with a slight reduction in detections from May to July particularly among the more inshore sites. Ambient sound levels (root-mean-square sounds pressure level; SPL) varied by site and season in relation to species presence, anthropogenic contributions, and environmental conditions. Monthly median SPL across the array varied up to 18 dB within 1/3-octave bands. Throughout the year, variability in median SPL was lowest in the higher frequency bands (>10 kHz), while highest variability was found between January to July in specific lower frequency bands (<1 kHz). Results from this study demonstrate the value of passive acoustic data in providing novel baseline information about cetacean occurrence and distribution in Scottish offshore habitats where data are limited and outdated. The results will feed into statutory reporting on underwater noise, support the identification and designation of future marine protected areas for cetaceans, and help guide management of future human-marine mammal interactions in Scottish offshore waters.</p