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Static Acoustic Monitoring Systems

The developments of oil and gas exploration and production, offshore wind, wave and tidal activity around the world has raised concern about the general ‘health’ status of the oceans.

The developments of oil and gas exploration and production, offshore wind, wave and tidal activity around the world has raised concern about the general ‘health’ status of the oceans. In Europe, the Marine Strategy Framework Directive (MSFD, http://ec.europa.eu) has compelled European states to develop policies of compliance with various descriptors, such as the achievement of ‘Good Environmental Status’. With respect to potential effects of underwater anthropogenic (man-made) noise on marine mammals, new marine regulations stipulate that potential impacts must be assessed prior to, during and following construction activity, particularly in the marine renewables sector, where potential effects are understudied considerably.

One of the most effective ways to achieve monitoring is by using Static Acoustic Monitoring Systems (SAMS). These are moored subsurface hydrophones that detect, store, process (and in some cases remotely transmit) underwater sound. There are two forms of SAMS: broadband acoustic spectrum recorders, which can monitor ambient/anthropogenic noise and marine mammals and SAMS that monitor marine mammals alone.

Traditionally, marine mammals are monitored using towed hydrophone arrays (see www.towedhydrophonearrays.com), which are a subdivision of broader Passive Acoustic Monitoring (PAM) systems. Passive Acoustic Monitoring is differentiated from active acoustic monitoring systems (such as those used by the military to detect divers and submarines, and more recently marine mammals near to underwater turbines), because of its un-intrusive (passive) nature (see www.passiveacousticmonitoring.com). Static Acoustic Monitoring Systems ensure no additional anthropogenic sound is inputted into the environment.

Ocean Science Consulting (OSC) Ltd. has been using SAMS since their conception in 2004 to detect echolocation vocalisations of odontocetes (toothed whales) in concurrence with offshore industrial processes, which create anthropogenic noise. Static Acoustic Monitoring Systems are also used commonly in Environmental Impact Assessments (EIAs), and in conjunction with Marine Mammal Observers (MMO; see www.marinemammalobserver.com).

The C-POD (see www.cpodclickdetector.co.uk), successor to the well-established analogue T-POD (see www.t-pod.co.uk), is at the forefront of SAMS. The C-POD is a cost effective, independent static unit comprising a large diameter omni-directional hydrophone, impact assessed transducer, digital timing/logging system, cell unit, digital processor and analysis software enclosed within a polypropylene shell.

Ocean Science Consulting’s research

Ocean Science Consulting is a world leader in the research, supply and use of SAMS in science and industry globally. Further details of these services can be found at www.osc.co.uk. Ocean Science Consulting’s scientists were the first in the world to detect harbour porpoises (Phocoena phocoena) using offshore rigs as feeding stations. This revolutionary discovery was published in a peer-reviewed journal (see http://icesjms.oxfordjournals.org). In May 2013, Marine Scientist also covered the work (http://eshop.imarest.org). All OSC’s research articles can be download here (www.osc.co.uk). Further research, instigated by OSC’s studies, suggests that shipping exclusion zones surrounding offshore platforms as well as the installations themselves act as vital habitats supporting a huge diversity of life. The rig to reef theory shines light on a positive effect of offshore industry.

After presenting preliminary findings into porpoise echolocation to the Institute of Acoustics (www.ioa.org.uk), OSC were commended for their success; the University of Edinburgh awarded two OSC research grants (www.maths.ed.ac.uk) to further extend their studies.

Current applications within research and industry

Static Acoustic Monitoring Systems are being used increasingly at the cutting edge of marine bioacoustics. The Static Acoustic Monitoring of the Baltic Harbour Porpoise (SAMBAH) project (www.sambah.org) chose to use large arrays of C-PODs, to determine the density and distribution of harbour porpoise populations in the Baltic Sea. Recent results show harbour porpoises exhibit seasonal variation in presence within waters surrounding Kriegers Flak windfarm in Denmark. Further windfarm construction is planned in the area and C-POD data may help to minimise potential effects of construction on local porpoises.

Static Acoustic Monitoring Systems, particularly the C-POD, are now the industry standard in marine acoustics, though there are still cases where the T-POD is more appropriate and still very much in use. Biological impact assessments of offshore activity (e.g. windfarm piling, seismic surveying, military exercises) have used SAMS to monitor the behaviour of marine mammals around both active and inactive operations. Results taken from the construction of the Alpha Ventus (first) offshore wind farm in the German North Sea (http://en.wikipedia.org) suggest that during periods of high intensity sound production, there was a high avoidance response from harbour porpoises. Other long term windfarm studies such as those carried out at Horns Rev (http://en.wikipedia.org) and Nysted (http://en.wikipedia.org) sites in Denmark suggest that marine mammals (grey seals, Halichoerus grypus and harbour porpoise) returned to the area once construction had finished.

The versatility of SAMS allows C-PODs and T-PODs to be surface or subsurface moored. Recent studies using bottom mounted SAMS (DOI: 10.1111/j.1748-7692.2010.00457.x) have suggested that, during operation of multi-ship active military sonar, Blainville’s beaked whales (Mesoplodon densirostris) also exhibit an avoidance reaction. Findings such as these are paramount in construction and enforcement of offshore industry guidelines.

Ocean Science Consulting

Ocean Science Consulting has provision to supply all equipment (including their own category 3 research vessel, Porpoise), and associated software along with expert engineers and operators. For further details on our other scientific services, refer to www.osc.co.uk.