ASA 126th Meeting Denver 1993 October 4-8

4aAB2. Walrus response to offshore drilling operations.

Jay Brueggeman

Ebasco Environmental, 10900 N.E. 8th St., Bellevue, WA 98004

Walrus response to drilling operations in the Chukchi Sea was evaluated between 25 June and 19 October, 1989. Aerial and vessel observations of walruses were conducted at three prospects in conjunction with acoustic measurements of the operations. Walrus response was evaluated before, during, and after they passed the drillsite relative to various sound sources. Over 350 groups comprising approximately 4500 walruses were observed in the prospects. Walrus response was greatest during ice management, when the icebreaker crisscrossed the prospect. Animals moved deeper into the pack ice, where the noise level from the icebreaker was an estimated 15--25 dB above ambient (97 dB). Once ice management stopped or became more focused at the drillsite, walruses began to reoccupy formerly used areas. Under these circumstances, walruses displayed some behavioral responses that rapidly decreased beyond 0.46 km (0.25 nmi) from the icebreaker. Walruses showed little response to other drilling operations. These results show that walruses reacted to icebreaker activities, but responses varied according to the intensity of ice management. This variability offers opportunities to incorporate precautions to minimize disturbance to walruses during future drilling operations.