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USGS Open-File Report 03-474, G1-03-GM, Gas Hydrates Cruise Report, R/V Gyre, 1-14 May 2003, Northern Gulf of Mexico

Marine Mammal Mitigation

With new regulations protecting marine mammals and endangered species, cruise G1-03-GM prepared for marine mammal mitigation by submitting a request for Incidental Harassment Authorization (IHA) to NOAA/National Marine Fisheries Service (NMFS). This request outlined proposed source sizes, decibel levels, likelihood of incidental "take," and proposed mitigation procedures to avoid harassment of marine mammals within the survey areas. The proposed mitigation procedures included contracting observers to watch for marine mammals during daylight hours, monitoring work areas for 30 minutes prior to start of seismic sources, not beginning new seismic operations or resuming seismic operations after a shutdown during the night, and establishing impact or safety zones for each seismic source to be used. These safety zones were defined by the radius to the 180 dB or 160 dB isopleth and seismic sources would be turned off if marine mammals enter the zone. Table 2 summarizes the safety zones proposed.

Copies of the NOAA/NMFS permit, the cover letter to NOAA, the request for IHA, the request to MMS, and the final marine mammal report are given in Appendix 3. Mary Jo Barkaszi and Richard Holt of ECOES were the contract marine mammal observers aboard the Gyre.

Table 2: Proposed Safety Zones for Acoustic Sources used on G1-03-GM

Seismic Source Sound Pressure Level (SPL) Re 1 microPascal-1 m rms 160 dB radius 180 dB radius
Huntec boomer 205 dB 175 m 17 m
Edgetech 512I chirp 198 dB 75 m 8 m
15 in3 water gun 204 dB 170 m 15 m
35/35 in3 GI gun 208 dB 250 m 25 m
24/24 in3 GI gun* 208 dB* 250 m 25 m
13/13 in3 GI gun* 204 dB* 170 m 15 m

*The safety zones and SPL values for the GI gun in 24/24 in3 and 13/13 in3 configurations were not proposed at the time of request for authorization but were determined later by comparison with similar seismic sources.

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Title Page / Abstract / Introduction / Acknowledgments / Geologic Settings / Cruise Objectives / Cruise Strategy / Instrumentation / Data Processing / Data Handling / Marine Mammal Mitigation / Operational Summary / Meeting Objectives Success / Summary / References / Appendices
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