Seismic Survey Mitigation Measures and Marine Mammal Observer Reports

Report

Title: Seismic Survey Mitigation Measures and Marine Mammal Observer Reports

Author:

Barkaszi, M.; Bulter, M.; Compton, R.; Unietis, A.; Bennet, B.

Publication Date:

June 1, 2012

Document Number:

BOEM 2012-015

Pages:

Affiliation

GeoCet Group LLC

Sponsoring Organization:

Bureau of Ocean Energy Management (BOEM)

Stressor:

Noise

Receptor:

Marine Mammals, Cetaceans

Document Access

Website:

External Link

Attachment:

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Citation

Barkaszi, M.; Bulter, M.; Compton, R.; Unietis, A.; Bennet, B. (2012). Seismic Survey Mitigation Measures and Marine Mammal Observer Reports (Report No. BOEM 2012-015). Report by GeoCet Group LLC. Report for Bureau of Ocean Energy Management (BOEM).

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Abstract

Mitigation observation data were collected during seismic survey operations in the Gulf of Mexico (GOM), United States of America (USA) between December 2002 and December 2008 under Notice to Lessees (NTL) 2007-G02 and earlier versions. The required submissions included observer effort, record of operations and sighting report data forms within each biweekly report.
A total of 1,440 bi-weekly reports were received by the Bureau of Ocean Energy Management (BOEM), formerly the Minerals Management Service (MMS), for seismic surveys; a total of 194,273 visual survey hours were recorded.
Visual observations yielded 3,963 complete sighting records; approximately 28,000 individual animals were represented in the records.
Cetaceans comprised 3,335 (85%) of these records with 20 species identified. Sea turtles comprised the remaining 579 (15%) records with five species identified. The most common cetacean encountered was the sperm whale, Physeter macrocephalus (N=1,136 records); the most common small cetacean identified was the pantropical spotted dolphin (Stenella attenuata), (N=740 records).
There were 32,939 ramp-ups recorded within all bimonthly reports. Of these records 65% were fully complete or nearly complete so that ramp-up activity and compliance were clearly discernible. Of the ramp-ups recorded, 90% were between 20 and 40 minutes in duration, as required by the NTL.
Of the daytime ramp-up records 86% had data complete enough to discern compliance with the pre-firing survey requirement. Only 3% of the pre-firing surveys were less than the required 30 minute duration.
There were 32 delays in ramp-ups due to the presence of protected species in the exclusion zone during the 30 minutes immediately prior to ramp-up. Of these delays, 24 (75%) were due to dolphins, four (12.5%) due to sea turtles, and four (12.5%) due to sperm whales.
There was a total of 18.5 hours of down time attributed to ramp-up delays.
There were 144 occurrences of whales visually detected in the exclusion zone that resulted in a shutdown of airguns. Of the required 144 shutdown events, 139 (97%) were due to sperm whales.
The average downtime resulting from shutdowns was 58 minutes and there was a total of 125.74 hours of down time attributed to shutdowns.
Shut down frequency for sperm whales was 0.71 shutdowns per 1,000 hours of observation, resulting in an estimated 1 shutdown for every 1,500 hours (or roughly 125 days) of daylight survey operations, assuming observations are conducted during all daylight hours regardless of gun operations.
The mean dolphin sighting frequency decreased 9% during airgun ramp-up procedures when compared to airgun silence. However, dolphin sighting frequency during minimum source firing sightings was equal to that during gun silence. Dolphin sighting frequency when airguns were at full power increased 14% when compared to silent mode.
The minimum distance of dolphins to airguns increases from silent, to ramp-up, to mitigation, and full power. At full power, the mean closest approach of dolphins to airgun arrays was 90% further away than during silent status.