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Soundings Archive

Marathon Oil Requests NMFS Permit for Seismic Operations in Cook Inlet
Marathon Oil Company has filed an application with the National Marine Fisheries Service for a permit that authorizes the incidental taking by harassment (Level B as defined in 50 CFR 216.3) of small numbers of marine mammals during Marathon's planned geophysical project in the North Ninilchik region of Cook Inlet from October 1 to no later than November 30, 2007.

Marathon's application states that its proposed seismic operations may have minor behavioral effects on Beluga Whales, Harbor Porpoises, Killer Whales, Harbor Seals, and Northern Sea lions.

Marathon states that its proposed seismic operations are unlikely to expose marine mammals to airgun noise above 160 dB, but that "[t]emporary, short term disturbance reactions (Level B) are likely amongst some small number of marine mammals in the general vicinity of the project when air guns are activated."

Marathon proposes to use the following exclusion zones or safety radii for marine mammals during its airgun use:

Estimated distances sound levels > 190, 180, and 160 dB RMS might be received from an array of 6 airguns used in seismic surveys in Cook Inlet.

Seismic Source

190dB

(Safety Criterion for Seals, Sea Lions)

180dB

(Safety Criterion for Whales)

160dB

(Assumed Onset of Behavioral Harassment)

880 cu in Bolt Airgun array with 6 airguns including

3 @ 225 cu in and 3 @ 75 cu in

<0.220 km

(0.14 mi)

<0.688 km

(0.43 mi)

<3.923 km

(2.44 mi)



Marathon's application includes the following statement distinguishing oil and gas seismic airgun operations from Navy sonar:
    "Strandings and Mortality "There is no evidence in the literature that airgun pulses can cause serious injury, death, or stranding of marine mammals even in the case of much larger airgun arrays than planned for the proposed program. While strandings have been associated with military mid-frequency sonar pulses, Marathon Oil Company does not plan to use such sonar systems during the 2007 seismic program. Seismic pulses and military mid-frequency sonar pulses are quite different. Sounds produced by airgun arrays are broadband with most of the energy below 1 kHz. Typical military mid-frequency sonars operate at frequencies of 2-10 kHz, generally with a relatively narrow bandwidth at any one time. Thus, it is inappropriate to assume that there is a direct connection between the effects of military sonar and seismic surveys on marine mammals."
NMFS has not yet published the Marathon permit application in the Federal Register for public comment.
  • Click here to read Marathon's application
  • Click here to read Draft Supplemental Environmental Assessment

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