Exploring the link between medium-frequency soundscapes and whale behaviours during foraging and migration.
Studying possible links between sounds and baleen whales' behaviour means solving three complex problems at once:
- First, marine soundscapes are always changing and are very diverse.
- Second, we don't know what baleen whales actually hear.
- Third, we understand little on how sounds they produce are disturbed or altered by other environmental noises, and how this affects their behaviour.
Our approach has been to focus on one species, the humpback whale (Megaptera novaeangliae), because they migrate over large distances and emit a very broad range of sounds. This provides us with a wide range of conditions to work with. In addition, there is a rich literature on humpback whale vocalisations with respect to specific behaviours (communicating, migrating, mating and foraging).
We also focus on the medium-frequency (200-2000 Hz) soundscape. In our model, we mix sounds produced by whales for echolocation (either when feeding or migrating) with sounds produced by ships propellers, at the same frequency. For this, we compiled statistics of maritime traffic to simulate the resulting noise level in the global ocean. We use this information with our migration model (developed earlier in the project) to simulate the risk that a humpback whale individual could lose their ability to feed or detect topographic changes while migrating where the ocean gets ‘noisy’.
A selection of spectrograms calculated for humpback whales with and without ship traffic sounds. Our preliminary estimates suggest that most of the risks are concentrated in the northern hemisphere and on continental shelves. This situation may have a significant effect on feeding behaviour and therefore, on the energy budget of the whales. On the contrary, our initial simulations suggest little or no effect for strandings.