Scientists present the first basin-wide map of the Mediterranean reflecting the density of underwater noise sources in the region

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There are several clearly identifiable areas within the Mediterranean basin where noise-producing activities accumulate. Many of these so-called noise hotspots overlap with significant cetacean habitats. This is a conclusion reached by scientists from France, Italy, Switzerland & the US who – for the first time – present a basin-wide map that shows the density of the main anthropogenic noise sources in the Mediterranean Sea. The results of the report ”Overview of the Noise Hotspots in the ACCOBAMS Area, Part I – Mediterranean Sea” for the period 2005 to 2015, are drawn from a dataset covering 1446 harbours & marinas, 228 oil drilling platforms, 830 seismic exploration activities, 7 million ship positions, publicly available information regarding military activities, & 52 wind farm projects.

Photo Credit: Giovanni Bearzi Tethys

Photo Credit: Giovanni Bearzi Tethys

The increase in seismic activities is particularly striking, especially in connection with oil & gas explorations which deploy so-called ‘airguns’ sending loud impulsive noise of up to 260 decibels towards the sea floor approximately every 10 to 12 seconds for weeks or months at a time. While 3.8 % of the Mediterranean’s surface was affected by such airgun use in 2005, this share increased to 27 % in 2013. The scientists moreover found that an average value of around 1,500 commercial vessels are contemporarily present in the area – at any given time – not taking into account leisure crafts & fishing vessels. Considering that data surrounding military activities – such as manoeuvres, use of medium & low frequency sonar for submarine detection, etc. are generally not available to the public, such results for this sector represents an underestimation of the reality of the situation as well.

Crucially, through such mapping exercise, the scientists were able to reveal several noise hotspots overlapping with areas that are of particular importance to noise-susceptible marine mammal species, and/or areas that are already declared protected areas. Such significant cetacean habitats include the Pelagos Marine Mammal Sanctuary in the Ligurian Sea, the Strait of Sicily, & parts of the Hellenic Trench, as well as waters between the Balearic Islands & continental Spain where noise-producing activities accumulate, according to the report. The risk for the marine animals in such areas is thus high, as they are exposed to cumulative & synergistic noise, & hence, extensive sources of stress.

Such threat has moreover been recognised by the Spanish Government. Their Ministry of the Environment recently announced that the waters between the Balearic Islands & the Spanish mainland will be designated a protected migration corridor for whales & dolphins, which will moreover result in strict management measures for noise producing activities.

“This report is the first basis for a purposeful development of noise reducing measures. It substantiates the urgent need for action to establish a transparent data register on anthropogenic noise sources in the Mediterranean & to take measures to reduce the problem”, says Silvia Frey, PhD, co-author of the report & director for science & education at OceanCare. Implementing such a register is moreover part of the EU Marine Strategy Framework Directive’s current action plan.

“With this report, we stand at the beginning of an acoustic assessment of the Mediterranean Sea as a marine habitat. Thus far, only noise sources which are timely & spatially incomplete could be identified. Hence, there is further need for scientific investigations into noise levels within the Mediterranean and, moreover, into what can be assessed as an acceptable & safe noise limit. Nevertheless, this first glance is remarkable & the extent of the noise sources is worrisome”, explains Frey.

“The present mapping moreover reveals data weaknesses, as we have to assume that some areas currently identified as ‘quiet’, particularly along the coastline of Northern Africa, are only considered quiet due to a lack of data. In particular, activities by oil & gas companies, as well as the military remain largely obscure”, adds Nicolas Entrup, consultant on underwater noise pollution for OceanCare & for US-based organisation NRDC.

“For the first time we have a wide spatial & temporal vision of the multiple & often overlapping human activities that produce noise underwater & that may have synergistic & cumulative effects on marine life. We now need models to map sound levels & sound exposure. We should not forget that conservation moreover means ‘conserving the acoustic quality of the habitats’”, says Gianni Pavan, co-author of the report & professor of the University of Pavia, Italy.

“Human activities using loud noise sources appear to cover very huge portions of the Mediterranean Sea, and, of course, their impacts on marine wildlife propagate, regardless of human boundaries. Although far from being exhaustive, results shown in this study point out the need of a regulatory framework which takes into account the transboundary effects of man-made noise on the marine environment”, Alessio Maglio, co-author & scientist at SINAY SAS, adds.

Manuel Castellote, PhD, co-author & scientist at NOAA, concludes: “With this report we have barely grasped the tip of the iceberg when it comes to underwater noise occurrence in the Mediterranean Sea. A major concern is the amount of silent Mediterranean countries, silent when it comes to information sharing, not underwater silence!”

The report was commissioned by the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea & Contiguous Atlantic Area (ACCOBAMS) in order to identify areas of concern, to propose the need for further scientific assessment, as well as to deduce appropriate conservation measures.

The authors of the report are:

Alessio Maglio, responsible for marine environmental assessments, SINAY SAS, environmental consulting, France
Gianni Pavan, professor for terrestrial & marine bioacoustics, CIBRA-DSTA, University of Pavia, Italy
Manuel Castellote, PhD, scientist at the Cetacean Assessment & Ecology Program at the National Marine Mammal Laboratory of NOAA – National Oceanic & Atmospheric Administration, USA
Silvia Frey, PhD, director science & education, OceanCare, Switzerland

Visit the full press release here.

Photo Credit: Giovanni Bearzi Tethys

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