Whale protection measure impacts GOM seismic exploration

Aug. 20, 2002
New mitigation measures ordered by the US Minerals Management Service, effective Thursday, to protect sperm whales from underwater noise damaging to them will raise the cost of seismic exploration in the Gulf of Mexico.

Sam Fletcher
OGJ Senior Writer

HOUSTON, Aug.19 -- New mitigation measures ordered by the US Minerals Management Service, effective Thursday, to protect sperm whales from underwater noise damaging to them will raise the cost of seismic exploration in the Gulf of Mexico.

But the good news is that it won't be nearly as costly as the original proposal contained in a biological opinion by the fisheries division of the US National Oceanic and Atmospheric Administration (NOAA) that threatened to shut down seismic exploration at night and during other periods of limited visibility, said Gordon C. "Chip" Gill, president of the International Association of Geophysical Contractors, Houston.

IAGC officials worked fast to soften the potential impact of new mitigation measures introduced by MMS in mid-July through a final notice of federal Lease Sale 184 for the western gulf, scheduled Wednesday.

Gill claimed the biological opinion issued by NOAA in conjunction with that sale contains "a number of fundamental flaws that have resulted in some inappropriate and unwise stipulations."

In an Aug. 2 letter to Dr. William S. Hogarth, assistant administrator for fisheries at NOAA, Gill said, "The stipulations would result in some significant changes in the operation of seismic activities in the (waters of the outer continental shelf) that we believe are unwarranted and unnecessary. As a matter of fact, we believe some of the requirements could actually result in greater impacts on marine mammals."

IAGC officials claimed NOAA's original proposal, based on a noise level of 180 db in water depths of 200 m or greater, would set "an unwise and needlessly restrictive precedent" with an impact zone "that is much larger than needed in order to protect sperm whales."

That proposal was worded so vaguely, with no references to frequencies or other parameters, they said, that the required exclusion zone for whales could have been interpreted as extending as much as 5 miles radius around an airgun source. Such a large area would have been physically impossible to monitor, IAGC officials claimed.

However, the notice issued by MMS limits the exclusion zone to a much smaller radius of 500 m "at and below the sea surface" surrounding the center of a seismic airgun array and within the immediate vicinity of the survey vessel.

"That's the same requirement as in the North Sea," Gill told OGJ. "We know we can successfully monitor an area of that size."

The MMS notice also requires seismic crews to ramp up initial firing of their airguns, starting with a single unit of the lowest power and increasing at a rate of 6 db every 5 minutes until the entire array is operating at the desired intensity for a survey.

That, too, is normal procedure for marine seismic crews so as to "push" out of the adjacent area any marine animals that might be sensitive to underwater noise, Gill said. After all, he said, "No one wants to get a whale caught in their gear" of geophone "streamers" strung out some 8 km behind a seismic vessel.

Seismic workers must visually monitor the exclusion zone and adjacent waters for at least 30 minutes to make sure no sperm whale is present before starting to ramp up their array of airguns, said MMS officials. But once the airgun array is activated, workers may continue to work at night or in adverse weather conditions that limit visibility as long as the airguns keep generating a minimum 160 db of sound, on the theory that keeping a noise source in the water will continue to keep sperm whales out of the affected area.

The original NOAA proposal would have forced seismic crews to shut down operations anytime visibility conditions deteriorated to the point that visual monitoring of the affected area was impossible.

Forcing such shutdowns, with subsequent ramp-up periods as visual conditions improved, could double the cost of marine seismic surveys by doubling the time it takes to collect seismic data, in a "worst-case scenario," said Gill. "Assuming we're shut down at night, we can only be shooting half the time."

Moreover, he said, forcing one seismic crew to shut down would wreck the "time shares" coordination required for multiple seismic crews to survey the same area for different clients, with one crew shooting its survey while another crew is making its turn and aligning its arrays of airguns and geophones for its next pass through that area.

In another victory for IAGC, MMS officials ruled that seismic contractors may delegate seismic crew members to do visual monitoring for whales "until trained visual observers can replace them. All seismic vessels must have trained observers for visual monitoring requirements within 2 months of the effective date (Aug. 22) of this NTL (notice to lessees and operators)."

Furthermore, MMS stipulated that seismic crew members could qualify as trained visual observers if they successfully complete a training program approved by NOAA. "Originally, NOAA Fisheries proposed to put its own people on our boats as observers," said Gill. "We'll have to add personnel, with observers probably working 4-hour shifts."

In letters to NOAA and MMS officials, Gill questioned the "scientific justification" for the 180 db sound threshold set by NOAA. In written comments submitted to government officials, IAGC representatives asked, "What is it based on? Why is 180 db safer than, say, 190 db? The number has not been referenced in terms of frequency band. It is not clear whether it is computed as a root mean square value over a time window, or whether it is a zero-to-peak value, or a peak-to-peak value. It is not clear whether it is to be computed from the vertical emission from the airgun array or from the horizontal emissions."

It was that ambiguity that could have established a 5 mile radius around an airgun array, said Gill.

In his letter to the NOAA, Gill cited "several basic technical issues that we believe grew out of a fundamental misunderstanding of airgun acoustic emissions and their potential impact on sperm whales."

He also noted that the unnamed author of that opinion apparently was unfamiliar with "scientific research conducted last summer that suggests that seismic operations may not pose displacement problems for sperm whales."

Under a joint research effort between MMS and the National Marine Fisheries Service, a satellite tracking tag was attached to a sperm whale last year in the Gulf of Mexico south of the Mississippi River delta. The whale's movements were then monitored from the time of the tagging in late July until mid-November 2001. According to data presented at an MMS meeting in New Orleans in January, that whale remained in "a relatively small" 130-by-130-sq-mile area of the gulf during those 5 months.

"During that same time period, an active 3D seismic survey was conducted near the center of the animal's foraging area," said IAGC officials in written comments on NOAA's proposal. Moreover, they said, "The principal investigator on this part of the study has been furnished with detailed positioning information on the seismic source and is conducting a detailed analysis of the relationship between the whale's movements and the seismic activity, i.e., where the seismic source vessel was, relative to the animal, and whether the (airgun) array was active or not."

Although that study cannot be completed before Wednesday's lease sale, IAGC officials said, "These data do show that there is no apparent displacement of the animal away from the area during the time the seismic survey was being conducted."

Wednesday's sale marks the first opportunity for NOAA to "flex its regulatory muscle" by refusing to certify the necessary biological provisions unless MMS officials included seismic survey mitigation measures in the sale language, said Gill. "There's a lot of industry interest in this sale because of several new trends proven by recent discoveries," he said.

Sperm whales—among the largest animals on earth—are protected under the Endangered Species Act. As recently as the mid-1980s, those whales were not commonly known to frequent US waters of the Gulf of Mexico, said Gill. But by 1996, 400-600 of the huge mammals were estimated to be in the gulf, primarily in water depths of 1,000 m. Sightings of sperm whales in the gulf primarily have been in deeper waters along the edge of the continental shelf in a direct line from the mouth of the Mississippi River "in the main area of seismic activity," Gill said.

IAGC officials asked Hogarth to "rescind the biological opinion, or amend it in a manner that will lead to more reasonable and effective regulation of seismic operations in the OCS." Otherwise, they said, "the resulting stipulation in its present form has a high probability of seriously undermining the efficiency and economic viability of exploration and development seismic surveys in at least the western Gulf of Mexico (and likely the entire Gulf of Mexico) without providing meaningful or necessary benefit to the animals of concern."

Meanwhile, Gill said, NOAA is drafting a new set of mitigation measures for federal lease sales in 2003-05 that would supersede this initial proposal. IAGC is examining several means—including judicial action—of opposing any measure that members believe to be unnecessary or based on "faulty science," he said.

In their written comments, IAGC officials assailed the "apparent misconception regarding the frequency content of airgun emissions," which NOAA described as "between 100-900 hz, with one or two echoes typically below 100 hz," and including "a loud seismic shock centered at 2.5 khz, with little energy below 1 khz."

Instead, IAGC officials maintained, "Numerous at-sea measurements of pulses from various airgun arrays show that the predominate energy generated by airgun arrays is concentrated below 300 hz. This is a function of the physics of how acoustic energy is produced by the release of compressed air into the surrounding water column."

They said, "The underlying physics of airgun sound generation does not lead to the occurrence of a 'loud seismic shock centered at 2.5 khz' or the design of 'higher frequency systems centered between 25-45 khz,'" as NOAA officials claimed. Moreover, they maintain that previous physiological studies of the lower hearing limits for sperm whales "indicate there is little overlap between the predominate frequencies generated by airgun emissions and the sensitive auditory range of sperm whales.

"This divergence strongly suggests that the potential for negative physical impact on sperm whales from airgun signals has a very low probability," IAGC officials said.

They said previous third-party scientific studies of the sound "clicks" generated by sperm whales when communicating indicate "signals from airgun arrays would occur only at the very low frequency end of the click spectrum. In addition, airgun arrays are generally cycled at around 10-second intervals. Sperm whales click at much faster repetition rates. Therefore, the likelihood of interference to sperm whale communication from background airgun emissions is very low."

IAGC officials also point out that the airguns in an array are synchronized to fire at different volumes to improve the quality of return readings. "Given the wandering nature of both marine mammals and marine seismic exploration crews, there appears to be little chance that any particular population of mammals will be exposed to seismic signals for any length of time that could significantly effect the long-term viability of the population," they said.

contact Sam Fletcher at [email protected]