A complicating factor in the discussion of seismic sound energy as a disruptive factor to marine mammals is that of the size and scale of seismic surveys as they are conducted into the 21st century. Historically, seismic surveys tended to have a duration of weeks or months and to be localised, but with OBN technology, surveys can cover thousands of square kilometres of ocean and can continue for years, all of the time putting sound energy into the ocean 24 hours a day from multiple energy sources. One current example of this is the 85,000 square kilometre mega seismic survey contract signed by the Abu Dhabi national oil company ADNOC in 2018 with an estimated duration into 2024 across a range of deep-water areas, coastal areas, islands and shallow water locations. It may be very difficult to assess the long-term impact of these huge operations on marine life.