Subsea sound generated by seismic airgun arrays and other man-made sound sources in the deepwater Gulf of Mexico may be coming to the fore as an environmental issue during the next several years.
Federal agencies say they are under pressure to more vigorously enforce environmental laws and regulations that bear on potential detrimental effects of man-made sound on mammals.
This pressure has mounted with the recognition that sound levels in the oceans may have increased dramatically in the last 25 years and that seismic surveys, shipping, military, and research activities are contributors.
The deepwater gulf is arguably the premier economic exploration play in the U.S. and is anticipated as the primary source of gas production to offset declines from fields on the shelf (OGJ, Aug. 30, 1999, p. 27). Modern 3D seismic surveys on the leading edge of this effort sometimes cover hundreds of blocks and involve several months of acquisition time.
Currently the U.S. Minerals Management Service has little scientific data relating to disturbance of such wildlife that it could use to objectively evaluate permits for seismic surveys and other industry-generated sound in the deepwater gulf. Emphasis is mainly on mitigating the effects, if any, of industrial sound on sea life.
More data likely will become available in the next few years as the result of several regulatory proceedings and government, academic, and industry research efforts.
If evidence mounts that man-made sound levels harm marine life, geophysical contractors and oilfield operators could face delays, higher costs, and perhaps even greater restrictions on marine seismic acquisition operations.
Industry has the chance to provide technical and research input to most of the regulatory initiatives.
Marine mammals of concern include whales, dolphins, porpoises, and seals. Sea turtles are also potentially vulnerable.
Regulatory proceedings
Two main regulatory fronts for the issue are a 1999 environmental assessment (EA) of Gulf of Mexico geological and geophysical operations and pending re-authorization of the Marine Mammal Protection Act (MMPA) of 1972.
Continental Shelf Associates, Jupiter, Fla., under contract to MMS, has begun preparing an EA of gulf G&G operations. The EA is programmatic, which is different than a specific permit approval, and covers seismic and other types of geophysical surveys as well as geologic investigations.
The EA is to summarize existing knowledge and the results of any new research, but no new studies will be undertaken for the EA. One task is to opine whether seismic surveys affect mammals and list mitigation alternatives. The contract schedule calls for submission of a draft EA to MMS Jan. 14, 2000, and final EA June 1, 2000.
The National Environmental Policy Act of 1969 requires that new federal activities be examined for individual and cumulative environmental impacts. If the gulf EA concludes that G&G operations have the potential to significantly affect nearby sea life, it could recommend that MMS prepare a full environmental impact statement (EIS) to assess the potential impacts.
MMPA reauthorization is at an early stage. The act provides that "no steps should be taken regarding these animals that might prove to be adverse or even irreversible in their effects until more is knownellipse"
A congressional subcommittee has heard input from agencies involved with enforcement. At least one industry group is pursuing the submission of industry comments to that panel.
MMS, the National Marine Fisheries Service (NMFS) arm of the National Oceanic and Atmospheric Administration, and the U.S. Fish and Wildlife Service (FWS) are the main federal agencies charged with enforcing the MMPA.
Man-made sound in the oceans is considered to be an international issue, but no global or regional treaties exist at present that relate to all marine mammals.
Measuring sound
A great deal of data exist regarding sound levels in the oceans, but knowledge is quite limited about the effects of sound on marine life, regulators and industry spokesmen said.
The focus of discussion with regard to effect on mammals seems to hover around sources that produce 180-220 decibels at a radius where mammals might be expected to be present.
Explosives, another sound source, are the subject of permitting in connection with oil and gas production platform removal but have not been used in U.S. offshore seismic operations for several decades.
An expert panel of the MMS-sponsored High-Energy Seismic Survey (HESS) team expressed apprehension in 1997 about seismic frequency band sound levels above 180 dB re 1 ?Pa with respect to overt behavioral, physiological, and hearing effects on marine mammals in general. This assessment followed various activities in the Santa Barbara Channel, including a 3D survey for Exxon over the Santa Ynez Unit in 1995.
Sound is transmitted very efficiently through water, and sea animals use sound propagation to communicate and explore habitat. Most sound energy introduced into the oceans is from ships, but seismic surveys produce some of the highest levels of man-made sound in oceans.
MMPA language includes the term "take," the act of harassing, hunting, capturing, or killing marine mammals.
NMFS and FWS can grant permits, or "incidental harassment authorizations," to entities if the agencies decide that "take" levels are acceptable. Turnaround is 120 days. However, NMFS has no overall definition of what constitutes a "take" from an acoustic source, and research aimed at framing a definition is just beginning.
Two levels of harassment are recognized: A, injury; and B, behavioral disruption.
MMPA and the Endangered Species Act of 1973 overlap in the protection they provide to various marine mammal species.
A committee of the U.S. National Research Council, in a 1994 study, concluded that then-existing data were extremely limited and could not serve as the basis for informed prediction or evaluation of the effects of intense, low-frequency sounds on any marine species.
Two other publications that deal with sound in the oceans are Sounding the Depths-Supertankers, Sonar, and the Rise of Undersea Noise, by Michael Jasny and Joel Reynolds, published by the Natural Resources Defense Council, March 1999, and Marine Mammals and Noise, by W. John Richardson et al., published by Academic Press, 1995.
Mitigation alternatives
One simple means of reducing potential sound-related effects on mammals is to avoid areas where they are abundant or that are important for some aspect of a species biology, note MMS's Mark O. Pierson and others in a paper prepared for a Seismic and Marine Mammals Workshop, June 1998, London.
Marine seismic survey permits in some areas prohibit or discourage activities from taking place where and when marine mammals of concern are present.
Ramp-up or soft start-the gradual increase in intensity of a sound source from some base level to full operating intensity over several minutes-has become a standard mitigation measure in many areas. It is assumed that animals finding the sound offensive would move off, but no comprehensive study has evaluated this.
Some pinnipeds, especially sea lions, have been reported to approach operating seismic airgun arrays. NMFS directed the U.S. Geological Survey in a 1998 Puget Sound seismic survey to shut down if the source vessel approached a pinniped but not if the pinniped approached the array.
In recognition that mammals very close to an airgun array might sustain hearing damage, some agencies designate safety zones. These zones "are defined by the radii of received sound levels believed to have the potential for at least temporary hearing impairment for marine mammals," Pierson et al. wrote (see table, p. 105).
Joint Nature Conservation Committee, Aberdeen, U.K., has written guidelines for visual monitoring of marine life near the source vessel. Observation usually begins 90 min before start-up. If mammals are observed, the crew may delay ramp-up or shut down the array until they pass. Visual monitoring is less effective at night, and not all mammals swim on the surface.
Sea life detection can also involve aerial surveys and acoustic monitoring, both of which have limitations in seismic work. Research on sonar monitoring is not well advanced.
Some seismic contractors have tried bubble screens to retard the lateral spread of sound, but the data are either proprietary or unpublished.
Industry's response
Energy Research Clearing House, The Woodlands, Tex., plans to hold a one day seminar in mid-November 1999 to help broaden industry understanding of the issue's scope, said Gene Sparkman of ERCH. It coordinates collaborative upstream research.
Another upcoming meeting of interest is that of the Acoustical Society of America in early November in Columbus, Ohio.
The International Association of Geophysical Contractors, Houston, also will likely take a role in informing industry about the issue, said Louis Schneider of Edison/Chouest Offshore and an IAGC representative. Schneider and Jack Caldwell with Schlumberger Geco-Prakla head an IAGC committee related to the sound issue.
Another group that could provide input is the National Ocean Industries Association, Washington, D.C.
Other interested constituencies on sound in the oceans include acousticians, biologists, the military, and other researchers.
