Harbour and grey seals rely on acoustic signals to mate, socialise and defend their territory. Previous studies have focused on their behaviour, movements and communication from the coast, leaving a knowledge gap in the offshore environments, and therefore being unable to determine the proper use they give to those areas and the risks they face around them. Acoustic data collected with a SoundTrap were analysed to assess the detectability of both species in the Malin Sea. Vocalisations were classified based on aural and visual features, as well as using non-parametric classification trees. Differences in the vocalisation rate of grey seals per diel, season and tidal state were also assessed through Generalised Linear Mixed Models, obtaining significant results, and finding similarities in the vocalisations of grey seals with the Scottish and Irish populations. A small sample of adult and pup harbour seals was detected, and differences in call type and number of detections per type were found across the seasons. These results show the importance of the area for both species, and lay the foundations for future studies, which will help to implement proper conservation measures such as Marine Protected Areas.

Underwater vocalisations of grey seals (Halichoerus grypus) were recorded by static acoustic monitoring (SM2M, Wildlife Acoustics) in the vicinity of a colony located at White Strand beach on Great Blasket Island, southwest Ireland during the pre-breeding and breeding seasons. Grey seal vocalisations were first classified across nine different categories based on aural and visual characteristics of the spectrograms, providing an acoustic repertoire for grey seals. This classification was further investigated by applying a classification tree analysis, resulting in five of the initial nine groups being selected. Furthermore, a comparison of two common approaches for the detection and extraction of vocalisations from acoustic files was done using the software Raven Pro and PAMGuard. The outputs of this study will present an essential first step towards the development of a protocol for underwater acoustic monitoring of grey seals in Irish waters and elsewhere.

Snapshots of underwater sound were collected during a multidisciplinary research survey at 14 stations south of the Iberian Peninsula, including the Strait of Gibraltar, an area characterized by intense maritime traffic. Sound Pressure Levels (SPLs) were quantified at each station using 1/3-octave bands, with a focus on the 63 Hz and 125 Hz centered frequency bands, as recommended by the Marine Strategy Framework Directive (MSFD). When possible, the main noise sources were also identified. SPLs in the 63 Hz band ranged from 104.91 to 132.24 dB re 1 μPa, with an average of 113.21 dB re 1 μPa. In the 125 Hz band, SPLs ranged from 104.31 to 129.82 dB re 1 μPa, with an average of 110.27 dB re 1 μPa. The highest SPLs were recorded at the stations in the Strait of Gibraltar and the Alboran Sea. A methodology consisting of attaching a SoundTrap to the research vessel’s CTD rosette was tested and proved to be an effective approach for assessing the underwater soundscape from vessels of opportunity.

Static Acoustic Monitoring (SAM) using C-PODs, deep C-PODs, and F-PODs was conducted as part of the STRAITS project (Strategic Infrastructure for improved animal Tracking in European Seas), funded under the EU’s Horizon research and innovation programme, to investigate odontocete acoustic occurrence across four European straits: the North Channel, the Sound, the Strait of Gibraltar, and the Dardanelles Strait. The acoustic presence of dolphin species and harbour porpoises was modelled in relation to tidal cycle, moon phase, sea surface temperature (SST), diel period, season, and Sound Pressure Levels (SPLs), representing ambient underwater sound using a Generalised Additive Modelling (GAM) approach. Harbour porpoises were primarily detected in the Sound and the North Channel, while dolphin detections were higher in the Strait of Gibraltar and the Dardanelles Strait. There was a significant association with SPLs on both species across all locations where it was assessed. There was a significant effect of tidal cycle and SST on both species across all locations except the Dardanelles Strait. Temporal patterns were significant across species and study sites. This study presents the first multi-strait assessment of odontocete occurrence in key marine corridors, highlighting the relationship of environmental and temporal drivers, underwater noise, and odontocete occurrence, and providing insights for marine spatial planning and conservation management in highly trafficked regions.