Distribution and abundance of western gray whales during a seismic survey near Sakhalin Island, Russia.

Exxon Neftegas Limited, operator of the Sakhalin-1 consortium, is developing oil and gas reserves on the continental shelf off northeast Sakhalin Island, Russia. DalMorNefteGeofizika (DMNG), on behalf of the Sakhalin-1 consortium, conducted a 3-D seismic survey of the Odoptu license area during 17 August-9 September 2001. A portion of the primary known feeding area of the endangered western gray whale (Eschrichtius robustus) is located adjacent to the seismic block. The data presented here were collected as part of daily monitoring to determine if there was any measurable effect of the seismic survey on the distribution and abundance of western gray whales. Mitigation and monitoring program included aerial surveys conducted between 19 July and 19 November using the methodology outlined by the Southern California High Energy Seismic Survey team (HESS). These surveys provided documentation of the distribution, abundance and bottom feeding activity of western gray whales in relation to seismic survey sounds. From an operations perspective, the aerial surveys provided near real-time data on the location of whales in and outside the feeding area, and documented whether whales were displaced out of an area normally used as feeding habitat. The objectives of this study were to assess (a) temporal changes in the distribution and abundance of gray whales in relation to seismic survey, and (b) the influence of seismic survey, environmental factors, and other variables on the distribution and abundance of gray whales within their preferred feeding area adjacent to Piltun Bay. Multiple regression analysis revealed a limited redistribution of gray whales southward within the Piltun feeding area when the seismic survey was fully operational. A total of five environmental and other variables unrelated to seismic survey (date and proxies of depth, sea state and visibility) and one seismic survey-related variable (seg3d, i.e., received sound energy accumulated over 3 days) had statistically significant effects on the distribution and abundance of gray whales. The distribution of two to four gray whales observed on the surface (i.e., about five to ten whales in total) has likely been affected by the seismic survey. However, the total number of gray whales observed within the Piltun feeding area remained stable during the seismic survey.

Feeding of western gray whales during a seismic survey near Sakhalin Island, Russia.

Exxon Neftegas Limited, as operator of the Sakhalin-1 consortium, is developing oil and gas reserves on the continental shelf off northeast Sakhalin Island, Russia. DalMorNefteGeofizika (DMNG) on behalf of the Sakhalin-1 consortium conducted a 3-D seismic survey of the Odoptu license area during 17 August-9 September 2001. A portion of the primary feeding area of the endangered western gray whale (Eschrichtius robustus) is located in the vicinity of the seismic survey. This paper presents data to assess whether western gray whale bottom feeding activity, as indicated by visible mud plumes, was affected by seismic operations. The mitigation and monitoring program associated with the seismic survey included aerial surveys during 19 July-19 November 2001. These aerial surveys documented the local and regional distribution, abundance, and bottom feeding activity of western gray whales. Data on gray whale feeding activity before, during and after the seismic survey were collected, with the whales assumed to be feeding on the benthos if mud plumes were observed on the surface. The data were used to assess the influence of seismic survey and other factors (including environmental) on feeding activity of western gray whales. A stepwise multiple regression analysis failed to find a statistically significant effect (alpha = 0.05) of the seismic survey on frequency of occurrence of mud plumes of western gray whales used as a proxy to evaluate bottom feeding activity in Piltun feeding area. The regression indicated that transect number (a proxy for water depth, related to distance from shore) and swell height (a proxy for sea state) were the only variables that had a significant effect on frequency of whale mud plumes. It is concluded that the 2001 seismic survey had no measurable effect (alpha = 0.05) on bottom feeding activity of western gray whales off Sakhalin Island.