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Coastal and Marine Earthquake Studies

Western Coastal and Marine Earthquake Studies.


SHIPS: Seismic Hazards Investigation in Puget Sound

Preliminary Results of SHIPS Marine Mammal Injury Mitigation

John Calambokidis
Cascadia Research
218 1/2 W Fourth Ave.
Olympia, WA 98501
Tel. (360)943-7325
FAX (360)943-7026
Writing at 9:27:08 AM on 3/24/98


The marine mammal research and mitigation was conducted successfully during the US Geological Survey seismic exploration program SHIPS (Seismic Hazards Investigations in Puget Sound). This research was conducted by numerous researchers primarily with Cascadia Research, under contract to the USGS.

Mitigation efforts were successful in reducing the risk of injuries to marine mammals. On three occasions shut-down of the airguns was requested and immediately implemented in response to marine mammals being sighted near the vessel. On two additional occasions the airgun operations were voluntarily suspended by USGS as an added precaution while transiting areas of high densities of marine mammals or presence of gray whales. The survey route was also modified on several occasions to avoid areas of high marine mammal densities.

Research on the reaction of marine mammals to the airguns was also conducted successfully throughout the surveys. This should provide valuable new information on both how and at what distance marine mammals react to airguns. Research components included:

  1. Monitoring the distribution, movements, and behavior of marine mammals seen from the seismic ship (the Thompson). More than 468 sightings of nine species of marine mammal species were made from the survey vessel.
  2. Gathering data on the distribution and behavior of marine mammals from a second survey vessel. Over 330 sightings of eight marine mammal species were made at distances from near the seismic vessel out to more than 20 miles away.
  3. Examining the distribution of marine mammals in high-densities areas through repeated aerial overflights before, during , and after passage of the seismic vessel. Over 400 sightings of six marine mammal species were made during the surveys.
  4. Gathering data on the behavior of animals from smaller launch in relation to the measured sound levels they were exposed to from the airguns. Measurements of the propagation of the seismic sounds were conducted in a variety of habitats and varied distances.
  5. Conducting special small-boat surveys in sensitive areas, especially where gray whales were known to occur to document the number and identities of animals in these areas before and after passage of the seismic survey vessel.

The study was lucky to have extremely good weather conditions through most of the study. More marine mammals were seen during both the vessel and the aerial surveys than had been anticipated including: Harbor seals were the most abundant marine mammal seen with highest concentrations in Puget Sound. More than 300 sightings of harbor seals were made during the aerial surveys alone. California and Steller sea lions were seen in high numbers in several areas including Puget Sound Elephant seals are an occasional visitor to these waters and only a few were seen in the Strait of Juan de Fuca Harbor porpoise were seen primarily in the Strait of Juan de Fuca and around the San Juan Islands. Dall's porpoise were encountered in both Puget Sound and the Strait of Juan de Fuca. Gray whales were seen in two areas. Around Whidbey Island, a number of gray whales were seen feeding. These represented early arrivals of the "summer-resident" population of gray whales that annually feed in these waters. Several of these have already been individually identified and include two whales that have come to these waters for six or more years. At the western entrance to the Strait of Juan de Fuca, offshore of where the seismic surveys were conducted, gray whales were also seen along their normal migratory pathway. Minke whales were seen on several occasions in the Strait of Juan de Fuca. This species had been thought to be not as common this time of years as in the summer when most sightings are made. Data gathered for the marine mammal research will be compiled and analyzed over the next four months and a final report prepared at that time.

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