In order to look at the responses of marine mammals to underwater sound, usually one single loud sound source is considered in the models. In reality, marine mammals are exposed to multiple sound sources through time and space. But now a new modelling approach has been developed to allow models to incorporate sound levels from multiple sources.
This is a great advance in the world of impact modelling from a collaboration of key experts from various companies/groups worldwide. The paper outlines the model using bowhead whales migrating through the Alaskan Beaufort Sea as an example. Firstly the authors looked at what sound sources were generated during the study period then they simulated the whales moving through those sound fields. This allowed them to calculate the sound exposure level for each animal from each sound source and then estimate the combined exposure from all sound sources for each whale. Interestingly, they also ran two types of movement models: the first, where the animals could change their movement in response to sound (aversion response) and a second where the animals didn’t (i.e. no aversion response). The acoustic model they used was relatively simple, and included sound sources from seismic exploration and vessel traffic. However, with further testing and understanding, this model could be modified for more sophisticated and realistic simulations of noise exposure for individuals and populations.
Lets take the North Sea as an example. The multiple stressors could include sounds from:
- oil and gas platforms
- seismic exploration
- renewable energy devices
- infrastructure construction
All of which cause sounds that have the potential to impact marine mammals through injury and/or disturbance.
This kind of development, in the future could help us move towards quantitative assessments of population effects by considering multiple sources of noise (or other stressors) and so highlights the potential for other models such as PCoD to extend their abilities to model multiple stressors. This is a fascinating development in impact modelling and we look forward to seeing how it continues to develop and enhance our understanding of the potential impacts of anthropogenic sounds on individual animals and populations.
SMRU Consulting have been involved in several noise monitoring projects and have developed the interim Population Consequences of Disturbance (PCoD) framework to assess the population level impacts of noise disturbance on marine mammal populations. We have also been involved in assessing cumulative noise impacts from developments in the North Sea. Check out some examples here:
- cumulative impact assessment on harbour porpoises from piling activities in the North Sea
- Population Consequences of Disturbance framework
- forecasting potential effects of disturbance associated with Navy exercises at Navy ranges
- real time underwater noise level monitoring and mitigation
- real time remote underwater noise monitoring
- assessment of different offshore developments impacting harbour porpoises in the Netherlands