Assessing the possible acoustic impact of artificial sound sources on the marine environment is not a trivial task, for various reasons. The first reason is the relative lack of information about how marine organisms process and analyse sound. Furthermore, and even though we are now capable of recording and cataloguing most of these signals, we do not know their role and importance in the balance and development of populations. Secondly, the emitted sounds may not only have a possible impact on the auditory pathways, but can also interfere at other sensorial levels and systems, leading to the death of the animal exposed. Adding to these two already important reasons the fact that the consequences of short or long exposures to certain noise can have side or after-affects in the middle or long term, and therefore could be not immediately observed, one can understand, without excusing the lack of foresight or means for investigation, the large difficulties with which the scientific community is faced in order to obtain objective data that allow effective control over the introduction of anthropogenic noise in the sea.
In order to answer some of these questions, the choice of cetaceans, and the exhaustive study of their adaptations to the marine environment throughout their evolution, is not coincidental. The marine environment, like every natural environment, is managed by the equilibrium between the organisms that inhabit it, each one placed at a specific trophic level on the food chain that allows the development of the higher levels. Maladjustment in any of the levels will bring an imbalance to the chain, in both directions. Faced with a conservation problem, the scientific challenge is to find an organism that is representative enough, meaning whose balance and development have an influence on the balance and development of the rest of the trophic chain, and use it as a bio-indicator against the contaminating source. Cetaceans, because they almost exclusively depend on acoustic information to perform daily activities, represent the best bio-indicator to measure the effects of marine acoustic pollution.