Offshore hydrocarbon exploration and production (E&P) activities can overlap in space and time with marine mammal populations. These activities, especially seismic surveys, can generate loud sound levels that propagate well in the marine environment. Exposure of marine mammals at varying distances from the source of these sounds can result in a range of different impacts, from auditory injury to behavioral responses and masking. The pathway-receiver (SPR) model is a framework often used in environmental impact assessments. In this overview, the SPR model is applied to summarize the current understanding of (1) E&P impulsive sound sources such as airgun arrays and continuous sounds originating from drilling (source), (2) the propagation of sound generated by these sources through the ocean's water column (pathway), and (3) the impacts of these sounds on marine mammals (receiver). Potential unmitigated impacts of E&P activities on marine mammals can be categorized according to their impact severity and spatial scale, ranging from severe impacts occurring at a small spatial scale to lower level impacts occurring at larger scales (typically, but not always, in the following order: permanent auditory threshold shift - temporary auditory threshold shift - behavioral disturbance - masking). Available monitoring techniques, applied to enhance our understanding of marine mammals as related to the potential full range of E&P impacts from individual behavioral responses up to population-level consequences, are also described using the SPR model. Additionally, the range of mitigation measures applied in the E&P industry to prevent unacceptable impacts to marine mammals are provided and categorized according to a mitigation hierarchy (avoid > minimize > restore > offset). Finally, a case is made for application of the ALARP (As Low As Reasonably Practical) principle in seismic migration measures in specific E&P activities should be proportional with the assessed risk on marine mammal populations, as well as reasonably practicable to achieve.
