The last hundred years have seen the introduction of man-made noise into the marine environment on a scale hitherto never experienced during the ten million years of evolution of modern orders of cetaceans. It is therefore no small wonder that in this latest period of their history, whales and dolphins have not developed the capability to adapt their auditory apparatus to loud sounds.
Underwater noise pollution sources produced by human activities include:
- offshore oil/gas exploration and production,
- industrial and military sonar,
- experimental acoustic sources,
- underwater explosives and other underwater civil engineering activities,
- airborne noise from supersonic aircraft.
This artificial noise is introduced in the physical and acoustic space of the marine organisms and there is not yet threshold levels that would allow to predict the possible negative consequences of these interactions in a short, medium or long term on the balance of the sea.
The control of these sources constitutes a scientific challenge and involves an important responsibility from the society and the governments.
Although the negative effects of loud sound sources such as industrial activities, seismic exploration, and vessel traffic have been demonstrated in terms of avoidance and other changes in behaviour, it has been very difficult to determine whether man-made sounds actually lead to mortality.
However, it is becoming clear that man-made noise, at different intensity levels, can affect negatively cetacean populations, including displacement, avoidance reactions, collisions with ships, mass stranding and death. Evidence is particularly strong that high intensity active sonar, and other loud noise sources, like those from shipping, gas exploration, seismic surveys, etc., cause lesions in acoustic organs which are severe enough to be lethal. The same sources may also produce behaviours that cause acute lesions that eventually lead the animals to strand and die. The current scientific knowledge on the effect on noise on marine mammals and their habitat is insufficient to understand the relationships of frequencies, intensities, and duration of exposures in producing damage.
In light of recent mortality events, the Council of the European Cetacean Society (European Cetacean Society) wrote a statement concluding its 17th Annual Conference on Marine Mammals and Sound that considers:
- research on the effects on man-made noise on marine mammals is urgently needed , and must be conducted to the highest standards of science and public credibility, avoiding conflicts of interest;
- non-invasive mitigation measures must be developed and implemented as soon as possible;
- the use of underwater powerful noise sources should be limited until their short- and long-term effects on marine mammals are better understood, and they should not be used in areas important for cetaceans;
- legislative instruments must be developed that help to implement both national and European policies on marine noise pollution.
These new elements request a dynamic analysis of the situation which must go through the development and implementation of new technologies without slowing down human interests nor compromising the conservation of the marine habitat, if we want to avoid that human activities in the sea become in a short term a synonym of permanent loss of the natural balance of the oceans.