In the discussion about the effects of noise on marine mammals it is important to quantify natural and man-made noise sources not only in their intensity but also in their duration and occurrence rates. Marine mammals are subject to natural noise sources such as earthquakes and submarine volcanism. As far as it is known, areas of high seismicity and consequently high intensity events are repeatedly visited by marine mammals. Therefore, it must be assumed that they are adapted to such events, at least for a certain time period. In order to judge the effects of man-made noise to mammals, it is important to consider the duration of the acoustic disturbances within a season as well as the rate at which this disturbance occurs in a particular area over several years. The individual signal length but also the duration of a hydroacoustic survey plays an important role for the level of disturbance. A comparison of the style of seismic surveys shows that academic research programs carry out mainly line surveys once per area of interest (2-D seismic) with a line spacing of several kilometres, while the exploration industry has moved on to 3-D surveys, which comprise a detailed spatial investigation of the subsurface on seismic profiles a few tens of metres apart. Repeated surveys of a particular area are intended to monitor changes in reservoir fluids, pressures and stresses (4-D seismic). Seismic surveys for academic research in Antarctic waters south of 60 °S serve in most cases a reconnaissance role. The documentation of seismic surveys in Antarctica over the last twenty years shows that there had been not more than one seismic survey in a single survey season (December through April) in a particular region of a few thousand square kilometres. In many cases, seasons have even been skipped. On the average, each seismic survey lasted only a few days.