Strategic assessment of the risk posed to marine mammals by the use of airguns in the Antarctic: concepts, methods, results, and controversies

In 2008/9, the AWI prepared a comprehensive, strategic assessment of the risk posed to marine mammals by the use of airguns for geophysical research in the Antarctic Treaty area. Operational and environmental conditions of all seismic expeditions of the past 22 years are evaluated, to obtain a set of 4 representative environmental scenarios. For each of these scenarios, acoustic fields (SPL and SEL) were calculated by numerical (finite difference 2.5 D full waveform) modelling for 6 airgun characteristics, resulting in a total of 24 different acoustic scenarios. The current state of ecological knowledge, as relevant to this risk assessment, was compiled for 20 species to which this ocean region represents an important habitat. As specific noise exposure criteria for the Antarctic Treaty Area have not been specified yet, possible hazards and corresponding numerical and qualitative evaluation criteria were extracted on the basis of available, published information. Finally, by applying these criteria to the modelled acoustic fields, critical exposure zones were calculated and incorporated in the development of a set of dedicated mitigation measures to minimize possible risks. The talk will present concepts, methods and results of this study along with controversial issues that unavoidable are part of such studies.