Noise impact

Species have different hearing capabilities; therefore, different species are sensitives to different noise frequencies^{[1] [2]}. Modeling behavioral changes, such as changes in spatial distribution of acoustically-sensitive species in response to anthropogenic noise is particularly challenging due to the need for species-specific responses to defined noise frequencies layer(s) in an Ecospace model.

The importance of quantitative measures of noise frequencies produced in order to assess their impacts on sensitive species has been suggested^{[3] [4] [5]}. Baleen whales, for example, are sensitive to low-frequency (10-500 Hz) noise, and are therefore considered most at-risk from shipping noise^[6] and other low-frequency noise devices such as marine wind and tidal turbines^[7](Kikuchi, 2010). A recent study demonstrated that seals also responded to low frequency noise from ships by changing their diving behavior^[8]. Some high-frequency components (up to 160 kHz) of shipping noise can have substantial effects on higher-frequency sensitive cetaceans including harbour porpoises^{[9] [10] [11]}. In a recent study, harbour porpoises showed high sensitivity to acoustic deterrent devices (ADDs), originally designed to protect fish-farming cages from seals with potential habitat exclusion in coastal areas due to ADD noise^[12].

Because of the lack of information needed to create species response curves to defined noise frequencies, in Ecospace, the level of impact of noise was inferred by distance from the noise source^{[13] [14]}, which were either static, e.g. wind and tidal turbines^{[15] [16][17]} or dynamic, e.g. shipping^{[18] [19]}. Porpoises might cease their feeding behavior at distances from 1 km^[20] up to 7 km at which they no longer are seen to be affected^[21]. In Serpetti et al.^[22], sigmoid functions were used to build the response functions within the avoidance distances up to distances at which marine mammal species no longer are seen to be affected (Figure 1). The spatial modeling output revealed the species dislocation from the noise source (Figure 2). The map for harbour seals showed a trade-off between attraction and avoidance at different distances.

Figure 1 – Response functions of harbour porpoise and harbour seals^[23].

The Ecospace modeling approach has shown high sensitivity to the impact of noise assessed by ecological responses to distances from noise sources^{[25] [26]}, however these studies also highlighted the necessity of improving our knowledge of species-specific response functions to noise, as well as long-term impacts of constant noise sources and potential species’ capability of acclimation and habituation to background noise^{[27] [28] [29]}.