Abstract
During last decades, anthropogenic underwater sound and its chronic impact on marine species have been recognised as an environmental protection challenge. At the same time, studies on the spatial and temporal variability of ambient sound, and how it is affected by biotic, abiotic and anthropogenic factors are lacking. This paper presents analysis of a large-scale and long-term underwater sound monitoring in the Baltic Sea. Throughout the year 2014, sound was monitored in 36 Baltic Sea locations. Selected locations covered different natural conditions and ship traffic intensities. The 63 Hz, 125 Hz and 2 kHz one-third octave band sound pressure levels were calculated and analysed. The levels varied significantly from one monitoring location to another. The annual median sound pressure level of the quietest and the loudest location differed almost 50 dB in the 63 Hz one-third octave band. Largest difference in the monthly medians was 15 dB in 63 Hz one-third octave band. The same monitoring locations annual estimated probability density functions for two yearly periods show strong similarity. The data variability grows as the averaging time period is reduced. Maritime traffic elevates the ambient sound levels in many areas of the Baltic Sea during extensive time periods.
Highlights
EU’s Marine Strategy Framework Directive (MSFD) was adopted in June 2008 with the aim to achieve Good Environmental Status (GES) and maintaining the marine biodiversity of European marine habitats by the year 20207
The underwater ambient sound was expected to be a mixture of the natural sounds, mostly caused by wind driven waves, and the anthropogenic sounds, mostly produced by commercial ship traffic
The soundscape of the sea when covered with ice is www.nature.com/scientificreports expected to be very different when compared to the period when the sea is open[23]. This change was recorded in the middle of the Bay of Bothnia in the Baltic Sea Information on the Acoustic Soundscape“ (BIAS) sound monitoring location 11 during the winter of 2016
Summary
EU’s Marine Strategy Framework Directive (MSFD) was adopted in June 2008 with the aim to achieve Good Environmental Status (GES) and maintaining the marine biodiversity of European marine habitats by the year 20207. The monitoring of underwater sound can be imagined to be a network of cabled monitoring stations that sufficiently cover a given marine area Costs limit this kind of ambition and a realistic monitoring programme will entail only a few monitoring locations. In order to assess the levels of underwater sound in a big marine area that is the Baltic Sea a joint international cross-bordering effort is needed. First project of this kind was Life+ “Baltic Sea Information on the Acoustic Soundscape“ (BIAS) launched in 201219. This was affirmed by the SMHI open-access data from HIROMB BS01 oceanographic forecast model
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