BOEM releases report analyzing 6 years of GOM Visual Observer Data


The Bureau of Ocean Energy Management (BOEM) has released a report analyzing 6 years of Gulf of Mexico (GOM) visual observer data. The stated objectives of the report, “Seismic Survey Mitigation Measures and Marine Mammal Observer Reports,” were to summarize and synthesize seismic survey observer reports for the years 2002 to 2008; and make recommendations as to the effectiveness of mitigation measures and suggestions for improved mitigations.

1,440 bi-weekly reports were received by BOEM for seismic surveys in the GOM conducted between December 2002 and December 2008. Bi-weekly reports were reviewed and data from each of three standard forms (effort, survey, and sightings) within the reports were entered into databases. Data from three air gun activation modes (ramp-up, mitigation, and full power) were analyzed separately and each compared against sightings during which air guns were silent. Sightings of different species groups were analyzed separately for baleen whales, delphinids, sperm whales, and sea turtles. Also, an analysis was undertaken for all cetaceans combined (excluding sea turtles). Data analyses included two core methodologies. The first was the analysis of sightings collated by block identification for use in determination of sightings frequency per 1,000 hrs effort per block, average sightings duration per block, and the average closest distance of approach of animals to airguns per block. The second methodology comprised the analysis of individual sightings events for analysis of animal behavior in response to airgun firing modes.

The report concluded that there was a high level of compliance with regard to pre-firing surveys, shut-down requirements, ramp-up delays, and ramp-up times. Sighting duration was found to be longer during times of full power seismic source operation when compared to silence, for both the ‘delphinid’ species group and ‘all cetaceans’ group. Each species group was found to be sighted at significantly greater distances from the seismic source during full power when compared to silence, illustrating a level of spatial avoidance of the seismic source. It is also clear that the data have limitations regarding the collection, interpretation and analysis of behavioral observations in relation to their use in impact assessment.

32,939 ramp-ups were 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 BOEM. 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 air guns. 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 for all years combined. 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.

The full report is available here.


Staff Contact: Sarah Tsoflias

Category: marine_enviro_research | Sub Category: other_research

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