Within the United Kingdom Continental Shelf (UKCS) offshore region, the Joint Nature Conservation Committee (JNCC) is responsible for the provision of nature conservation advice (http://jncc.defra.gov.uk/page-4273). The JNCC have written guidelines to minimise potential effects of noise generated by industrial operations on marine mammals. Specific best practice guidance documents have been written by the JNCC for seismic surveys (http://jncc.defra.gov.uk/page-1534), hammer piling (http://jncc.defra.gov.uk/page-4274), and explosives (http://jncc.defra.gov.uk/page-4900). These guidelines have also been adopted for activities such as dredging and military sonar exercises.
Marine Mammal Observers (MMOs, www.marinemammalobservers.co.uk) are employed to monitor visually for marine mammals during industrial operations, and to advise marine operations crew and clients on JNCC guidelines. Industrial operations are often conducted over 24 hour periods, and visual observations by MMOs are not always appropriate. Current best practice measures thus state that the commencement of industrial activities during hours of darkness, low visibility, or when sea state is not conducive to visual monitoring, and should only occur if Passive Acoustic Monitoring (PAM; www.passiveacousticmonitoring.co.uk) is used. Passive Acoustic Monitoring is the use of hydrophones and specialised software to detect vocalising marine mammals. Considered to be the most reliable available technique for detecting marine mammals in poor visibility, PAM can also be used during good sighting conditions to augment MMO visual observations. Passive Acoustic Monitoring operators are required to configure and deploy PAM equipment (e.g. www.towedarray.co.uk), and to interpret incoming noise.
The PAM operator and system should ideally be situated on the source vessel or offshore installation (e.g. drilling rig or production platform). If the PAM system is deployed too far away from the sound source, there may be reduced chance of detecting marine mammals within the mitigation zone (defined as the area immediately around the sound source, usually 500 m). There are situations where it is not possible practicably to deploy the PAM system in the mitigation zone, e.g. during explosives. Depending on the stage of MMO/PAM operator’s watch, if a marine mammal is detected, there could be a delay in the start of operations.
If a PAM operator is on duty at the same time as a MMO, an agreed line of communication should be established to ensure accurate and timely cross-reporting of sightings/detections. This is extremely useful for both parties, as the PAM operator may detect a vocalising animal before the MMO. Additionally, if the MMO can inform the PAM operator of distance to the sighting, this can assist the PAM operator in gaining valuable experience in estimating acoustic detection range, bearing in mind that there is no evidence that animal(s) sighted are the same individuals as those detected acoustically.
MMO vs PAM operator
When implementing mitigation measures, all MMOs and PAM operators, regardless of prior experience, differ in their range estimation abilities. Marine Mammal Observers, are able to measure animal distance by eye, with the assistance of equipment such as a range stick (http://jncc.defra.gov.uk), reticule binoculars (www.osc.co.uk), or sextants (http://en.wikipedia.org/wiki/Sextant).. At present it is not possible to express the range accuracy of most PAM systems in numerical terms. For example, if a PAM system has a reported range accuracy of ± 300 m (although an exact number is most often unknown, and is dependent on a plethora of factors) an animal detected at 500 m, may in fact be 800 m away, but would still delay the start of operations. The mitigation zone applied by PAM operators thus reflects a cautionary approach to the acoustic detection limitation of the PAM system in use. Given that not all vocalising marine mammal detections can be localised, it is the responsibility of the PAM operator to determine whether the marine mammal is within the mitigation zone, and therefore warrants a delay in the start of operations. It is prudent to use the most accurate PAM system, and well qualified and experienced PAM operators.
Overall, MMOs and PAM operators have the same advisory role, and follow the same set of guidelines. Marine Mammal Observers and PAM operators must also complete JNCC forms and submit final reports, either independently or jointly, depending on client and/or permit requirements. Marine Mammal Observers can also be qualified dually as PAM operators to allow extra flexibility in the field. For example, if a duty MMO is also a qualified and experienced PAM operator should a thick fog roll in, their role switch to PAM operator could minimise operational downtime.
PAM systems and software
While a variety of PAM systems exist (www.pamsystem.co.uk), in industry, towed hydrophone arrays (www.towedhydrophonearrays.com) are used most often for real-time marine mammal mitigation. The industry standard for software used to process and analyse marine mammal vocalisations is PAMGuard (www.pamguard.org). The JNCC encourages PAM operators, and industry representatives, to contribute to the development and refinement of this software
During permit application process, a brief description of the PAM system and deployment methods to be used may be required. The PAM station (i.e. where the PAM operator monitors) must be in a dry location with power, and ideally with access to the vessel’s National Marine Electronics Association (NMEA) feed for a GPS reading. Deployment methods vary greatly depending on the vessel/installation and type of work to be carried out. In general, a suitable winch should be made available, and deployment planned to minimise entanglement with other gear or contact with the sea bed. Given that background noise will affect the PAM operator’s ability to hear a vocalising marine mammal, Signal to Noise Ratio (SNR) must also be considered. For example, the hydrophones should not be deployed near any active thrusters or propellers.
For high quality PAM operators and equipment contact Ocean Science Consulting (OSC), or visit www.osc.co.uk