Oceans of noise - Whale and Dolphin Conservation Society

5. Noise as a problem for cetaceansChris Parsons and Sarah Dolman5.1 Particular cetacean vulnerabilitiesLack of knowledge means that risk assessment for cetaceans is most often based on assumptions.For example, it is assumed that those cetacean species with a hearing range within the range of anintroduced sound are likely to be most affected by the sound (with the possible exception ofexplosions and other such impulsive signals). Certain individuals within a group might beconsidered more vulnerable to noise; for example, mother and calf pairs. Similarly, those specieswith a poor conservation status, for example, endangered species, may be given special attention.The significance of introduced noise might also be given a higher priority where geographicaland/or seasonal areas of critical habitat have been identified.Deep-diving species such as the sperm and beaked whales may also be vulnerable as they travelinto zones where noise may be concentrated. These animals leave the surface with enoughoxygen in their organs and blood to sustain the dive, but may not have reserves to swim awayfrom intense and unexpected noise (Simmonds and Dolman 1999). An individual may not havethe capacity, particularly towards the end of its dive, to swim away from the introduction of anintense noise source.5.2 Short-term observationsIt cannot be assumed that no biological consequences result from exposure to loud noises whereno behavioural response is measured. However, in terms of determining if a noise is significant,consideration of behavioural responses might provide useful information. Identification ofsignificant behavioural responses requires that a cetacean’s normal behaviour (within theparticular circumstances under which they are exposed to the noise) is well categorised and thatchanges to it must be measurable and be able to be linked to the noise disturbance. It also requiresresearchers to be able detect changes in this behaviour, something which is particularly difficultwith animals which spend so much of their time out of sight, submerged beneath the surface.5.2.1 Disturbance and displacement reactionsHuman-introduced noise has been documented to induce short-term behavioural reactionsincluding cessation of feeding, socialising and vocalising, changes in diving behaviour as well asavoidance or attraction. In addition, noise has been documented as causing displacement ofcetaceans from preferred habitats. If these impacts were of only short duration they would notnecessarily be significant. However, if these disturbances are repeated or are of long duration,they may cause stress, debilitation and ultimately mortality.Approach, as well as avoidance of a noise source, should be considered as disturbance, becausean animal has altered its natural behaviour (Moscrop and Swift 1999). Individuals have been seento directly approach and investigate loud sources of noise which may place them in greaterdanger.Yet, displacement from a key habitat could have profound effects. Disturbance and displacementreactions caused by shipping traffic, for example, may have a significant negative impact andperhaps particularly in discrete coastal populations. These animals are besieged by a variety of54