Concern for marine mammals and their sensitivity to anthropogenic noise is putting pressure on marine industries to reduce the potential impacts of offshore activities such as piling, dredging, cable laying, sonar and seismic surveys. Research suggests that possible effects on marine mammals can range from hearing loss (Temporary Threshold Shift, TTS or Permanent Threshold Shift, PTS), to habitat displacement and avoidance behaviour. Additionally, if background noise levels are high enough, it can reduce the distance over which marine mammals can detect sound. This effect, known as masking, can prevent marine mammals from communicating with each other effectively, as well as reducing their ability to detect prey, avoid predators and sense the environment around them.
In order to minimise (positive or negative) impacts on marine mammals it has become commonplace for companies to produce a Marine Mammal Mitigation Plan (MMMP) before any marine work begins. A Marine Mammal Mitigation Plan presents details of strategies that will be used to limit the level of effects. Organisations such as the Joint Nature Conservation Committee (JNCC) in the UK (http://jncc.defra.gov.uk), the National Parks and Wildlife Service (NPWS) in Ireland (www.npws.ie), the Department of Conservation (DOC) in New Zealand (www.doc.govt.nz) and in the USA the Bureau of Ocean Energy Management, BOEM (www.boemre.gov) and the Bureau of Safety and Environmental Enforcement, BSEE (www.bsee.gov) have produced guidelines that advise on methods that should, and in some cases legally need to, be included when constructing a Marine Mammal Mitigation Plan.
Components of a Marine Mammal Mitigation Plan
The main methods used for reducing any potential disturbance in a Marine Mammal Mitigation Plan are temporal and spatial planning of offshore activities, the control of operational procedures, and the implementation of real time mitigation measures (www.marinemammalmitigation.co.uk).
Temporal & spatial planning of offshore operations
When planning work in the marine environment it is important to consider both the species that may be present, and the biological significance of the location in which the work will be carried out. A Marine Mammal Mitigation Plan will show, for example, if the area forms part of a migration route, in which case the peak of the species’ migration should be avoided. Similarly, if the habitat is used as a seasonal haul out site for seals or as a breeding or feeding ground for marine mammals, then work should be carried out at a time when the least amount of disturbance will be caused.
If nothing is known about the project area, a baseline assessment may be required. This usually involves monitoring the area for at least one year to determine seasonal trends in marine mammal distribution and behaviour. This can be done through visual surveys, static acoustic monitoring (e.g. www.t-pod.co.uk), real time passive acoustic monitoring (e.g. www.towedarray.co.uk), or a combination of the three. In the industrial arena, this baseline monitoring period is often restricted to a few weeks, which provides considerably less information, but can at least identify if the area is being used by marine mammals prior to, for example, a seismic survey.
Control of operational procedures
Operational procedures that produce high levels of anthropogenic sound should be performed using the Best Available Technique (BAT), which aims to reduce environmental impact whilst remaining practical and cost effective. Guidelines such as those followed by the UK, California and Brazil state that when carrying out seismic operations, the lowest practicable power levels should be used, to minimise the amount of unnecessary noise. Soft starts or ‘ramp ups’, defined as ‘the gradual increase in power over a period of time’, are another form of operational control that acts as a warning to marine mammals.
A Marine Mammal Mitigation Plan should also consider additional acoustic warnings that can be given to marine life in the form of sound producing Acoustic Mitigation Devices (AMD) or Acoustic Deterrent Devices (ADDs), such as low source level ‘pingers’ or the more intense ‘seal scrammers’ or ‘scarers’.
Other ways in which procedures can be modified to reduce noise levels, involve modifications to equipment; this can be done with the addition of acoustically isolating material to a hammering pile.
If used properly, these kinds of materials can assist in keeping noise production below required thresholds. For example, in one of Ocean Science Consulting’s main working areas, the German Federal Environment Agency, UBA (www.umweltbundesamt.de) has defined a threshold consisting of a dual criterion of 160 dB re 1 μPa²s (Sound Exposure Level, SEL) and 190 dB re 1 μPa2 (peak to peak sound pressure level) that should not be exceeded at a distance of 750 meters around a marine piling site. The threshold is based on a TTS found in a harbour porpoise (Phocoena phocoena) at 164 dB re 1 μPa2s (SEL) and 199 dB re 1 μPa2 (peak to peak sound pressure level). For more information on underwater sound measurements please see www.underwatersoundmeasurement.com.
Real time mitigation
Real time detection of marine mammals is an essential component of all Marine Mammal Mitigation Plans. The primary method of mitigation is visual watches by trained Marine Mammal Observers, MMOs (www.marinemammalobserver.com). The exact procedures vary depending on guideline requirements, but in essence, a pre-watch lasting between 30 to 90 minutes is undertaken before any noise producing work (seismic, piling, explosions etc.) commences. If an animal is sighted within the pre-determined exclusion zone during this time, then a delay in the start of work is advised. This gives the animals a chance to vacate the immediate area before the sound source is activated.
If visual watches are not possible due to weather restraints or lack of daylight, it is considered best practice to use Passive Acoustic Monitoring (PAM) systems (www.pamsystems.co.uk), which allow for real time acoustic detection of vocalising marine mammals.
Ocean Science Consulting and Marine Mammal Mitigation Plans
Ocean Science Consulting Ltd (OSC) is able to provide a comprehensive range of high quality services related to Marine Mammal Mitigation Plans.
Ocean Science Consulting can produce advice documents and Environmental Impact Assessments (EIAs) that will assist the production of Marine Mammal Mitigation Plans and help to ensure appropriate guidelines are adhered too. With our extensive knowledge base and experience in marine mammal science and underwater acoustics, OSC produces in-depth Marine Mammal Mitigation Plans renowned throughout the industry.
Our team of highly qualified Marine Mammal Observer, Marine Mammal and Seabird Observers, MMSOs, Protected Species Observers, PSOs, (www.protectedspeciesobservation.co.uk), Passive Acoustic Monitoring (PAM) operators (www.passiveacousticmonitoring.co.uk) in conjunction with our Ph.D.-qualified acousticians (www.underwatersoundmeasurement.com) and extensive range of both towed and fixed Passive Acoustic Monitoring (PAM) equipment (e.g. www.pamsystems.co.uk, www.cpodclickdetector.com), have all undergone extensive training and quality control. Our personnel can provide informative, up to date advice to our clients about the implementations of a Marine Mammal Mitigation Plan. All employees have a minimum of degree level education in a marine science, are fully insured with valid offshore survival and medical certificates. Additionally, staff have full access to specialist technical and logistical support from onshore sources round the clock to ensure the smooth running of all practices. We supply 100% redundancy to all equipment used in the field, and to-date, have ensured zero client operational downtime, saving our clients both time and money because of our staff’s high-level, fast-thinking decision making during complex operations.