Abstract
Effects of noise from seismic surveys on marine mammals need to be understood so that they can be appropriately mitigated. This study examined effects of large airgun arrays (79-110 l) on a variety of marine mammal species in the waters of British Columbia and Washington at long distances (1 to > 70 km). Received noise levels near marine mammals were measured to overcome difficulties in modeling long-range propagation in complex near-shore waters. Although airguns concentrate energy at low frequencies, noise was detectable to at least 100 kHz, providing a mechanism to affect marine mammals with good high-frequency hearing. Apparent behavioral responses varied by species. Species with similar hearing capabilities exhibited markedly different responses to airgun noise, and a high- frequency specialist, the harbor porpoise, appeared to be the species affected by the lowest level of noise ( 70 km). The long distances at which behavioral changes were observed indicate that long ramp-up times (>1-5 hours depending on species) are likely to be needed to prevent strong behavioral changes. While infrared imaging and passive acoustic monitoring can complement visual detection, technical constraints limit their usefulness. Scheduling surveys around seasonal distribution of species of concern, limiting periods of exposure, and routing airguns to ensure that marine mammals are not driven ashore may be as important as monitoring safety zones in preventing injuries and death.