The U.S. National Marine Fisheries Service issues Incidental Take Authorizations under the Marine Mammal Protection Act for seismic operations that might affect marine mammals. These authorizations usually include safety radii: i.e. areas around the seismic vessel that must be free of marine mammals during seismic operations. These areas have to be monitored for the presence of marine mammals. One commonly used monitoring method is visual observation. Another possible method is passive acoustic monitoring.
PAM uses software and hardware to listen to marine mammal's underwater vocalizations. In theory, PAM can determine whether marine mammals are nearby, even when they cannot be seen.
The Federal Register notice of a recent NMFS Take authorization describes how PAM is typically used in this regulatory context:
"Acoustical monitoring can be used in addition to visual observations
to improve detection, identification, and localization of cetaceans. The acoustic
monitoring will serve to alert visual observers (if on duty) when vocalizing
cetaceans are detected. It is only useful when marine mammals call, but it can
be effective either by day or by night and does not depend on good visibility.
It will be monitored in real time so that the visual observers can be advised
when cetaceans are detected. When bearings (primary and mirror-image) to
calling cetacean(s) are determined, the bearings will be relayed to the visual
observer to help him/her sight the calling animal(s)."
75 FR 8562, 8669 (Feb. 25, 2010), available online at http://www.nmfs.noaa.gov/pr/pdfs/fr/fr75-8652.pdf.
NMFS has even issued PAM guidelines, available online at http://www.acousticmonitoring.org/background/PAM_Guidelines_Lecky
NMFS staff have touted PAM as a regulatory tool at recent academic conferences. See power point at http://www.acousticmonitoring.org/materials/
A recent article by the Acoustic Ecology Institute describes "the revolution in passive acoustic monitoring." The AEI article predicts that PAM will be used for more than just monitoring mitigation safety radii in seismic Take Authorizations. This article contends that PAM will be integral to marine spatial planning and to developing sound budgets:
"Hydrophones have been finding more and more ways into the world without being suspended from boats or connected to recorders via long cords. Flash storage using far less energy than anything before is providing much longer recording times using very little battery power. And most exciting, engineers are developing ever more versatile platforms to carry these hydrophones, data storage, and associatedhardware across and into the ocean for longer and longer periods of time without human intervention.
The possibilities inherent in these breakthroughs are only beginning to be imagined. Among the first major research projects utilizing the new technologies is the widely- publicized work in Stellwagen Bank National Marine Sanctuary, which tracks individual whales and ships in real time, helping to avoid collisions as well as contributing to new insights about communication masking. Getting less attention, but equally exciting, are projects like Deep Sound, which is sending hydrophones into the deepest parts
of the world's oceans, and a multi-year project measuring ambient ocean noise in several places along the British Columbian coast, in part to see whether there are significant differences in shipping noise.
As the hardware behind such recording systems continues to offer more bang (data) for the buck, and the platforms on which they are deployed get simpler and cheaper, the long-time dream of being able to listen in on the world's oceans with enough 'ears' to create comprehensive sound maps is within reach. We will be able to learn just how much the acoustic ecology of busy ports is dominated by shipping noise, and more importantly, identify coastal areas where the soundscape remains rich and dynamic. Ocean planners will have access to localized, seasonal "sound budgets" that can inform the Marine Spatial Planning process that is beginning to unfold around the world."
Page 26 of report available online at http://acousticecology.org/spotlight_oceannoise2009.html.
The AEI article then discusses the most recent research in PAM. Its discussion will not be repeated here but it is highly recommended to anyone interested in this promising but still developing technology.