A new paper in published in Nature has found that harbour porpoises react to low levels of high frequency vessel noise. Odontocetes (toothed whales, dolphins, and porpoises) in particular rely heavily on the propagation of underwater sound for essential life functions including communication, navigation, and foraging.
OCEAN NOISE IS ON THE RISE and it’s important to determine the impacts of these changing conditions on cetacean populations.
Until now, the majority of studies have focused on the potential impacts of low frequency vessel noise on large baleen whales as the majority of sound produced by ships is of low frequencies and within their hearing range.
The authors exposed four captive harbour porpoises housed in a semi-natural net pen to recordings of a variety passing vessels and classified their behaviour as either a ‘reaction’ or ‘no reaction.’ A ‘reaction’ included typical avoidance behaviours such as an increase in swimming speed and/or porpoising. They found that the porpoises responded to mid and high frequency sounds and that nearly 30% of trials resulted in the stereotyped behavioural response of porpoising.
The impacts of high frequency vessel noise on cetacean behaviour has important implications for the management of these populations. Harbour porpoises typically inhabit shallow coastal areas where vessel traffic is high and where high frequency sounds travel better than those at lower frequencies. As a result, porpoises in the wild are routinely subjected to high frequency noise at distances of up to 1 km from passing vessels. The results of this study therefore suggest that high frequency vessel noise is a considerable source of noise disturbance that is currently being overlooked and that should be considered in the management of these species.