f Predicted Relative Effects of Marine Vibroseis Versus Airguns on Marine Mammals

Marine vibroseis (MarVib), if effective for geophysical purposes, might (relative to airguns) have reduced effects on marine animals. With Joint Industry Programme sponsorship, we prepared an Environmental Assessment (EA) of this possibility. Given the near-absence of specific data on biological effects of MarVib, most conclusions were based on indirect evidence. This presentation focuses on marine mammals, but the EA also addressed fish, turtles and invertebrates. With MarVib, higher frequency sound components (e.g., >100 Hz) should be reduced, benefitting species sensitive to sounds >100 Hz. Signal duration would be longer than for airguns, which could achieve similar source energy with lower peak pressures, thus reducing auditory and perhaps disturbance effects. Signal processing techniques applicable to MarVib might allow lower source energy per "shotpoint". There may also be more flexibility in the depth in the water column where a MarVib system could be operated. However, the higher duty cycle with MarVib may cause increased acoustic masking in species that rely on low-frequency sound. Also, with respect to behavioral disturbance, the higher duty cycle with MarVib may partly offset the benefits of the lower source level. Overall, use of MarVib rather than airguns would probably result in a reduction in some (but not all) types of impacts; controlled testing is needed. No extended abstract available.