Global reductions in the underwater radiated noise levels from cargo vessels are needed to reduce increasing cumulative impacts to marine wildlife. We use a vessel exposure simulation model to examine how reducing vessel source levels through slowdowns and technological modifications can lessen impacts on marine mammals. We show that the area exposed to ship noise reduces dramatically with moderate source level reductions that can be readily achieved with small reductions in speed. Moreover, slowdowns reduce all impacts to marine mammals despite the longer time that a slower vessel takes to pass an animal. We conclude that cumulative noise impacts from the global fleet can be reduced immediately by slowdowns. This solution requires no modification to ships and is scalable – from local speed reductions in sensitive areas to ocean basins. Speed reductions can be supplemented by routing vessels away from critical habitats and by technological modifications to reduce vessel noise.

For detailed information on the methods please see Findlay et al. 2023. Small reductions in cargo vessel speed dramatically reduce noise impacts to marine wildlife. Science Advances.

Software:

All code and custom-written functions were written in MATLAB 2021a (MathWorks, Natick, MA, USA).

Code/Functions:

Findlay_etal_ScienceAdvances.m

This file contains the code which will allow the user to reproduce components of Findlay et al. 2023. Small reductions in cargo vessel speed dramatically reduce noise impacts to marine wildlife. Science Advances. The associated custom-written functions are detailed below.

VesselSLSpectrumModel.m

This file is a MATLAB Version of the JOMOPANS-ECHO Vessel Reference Spectrum Model proposed by Alexander MacGillivray and Christ de Jong (2021).
REFERENCE: Macgillivray, A., de Jong, C., 2021. A reference spectrum model for estimating source levels of marine shipping based on automated identification system data. Journal of Marine Science and Engineering. 9, 1–15. https://doi.org/10.3390/jmse9040369.

areaExposed.m

This function will calculate the area exposed to underwater noise from fixed-pitch propeller vessels for a range of source level reductions as the percentage of max (100%). Area exposed includes the vessel noise swathe, instantaneous acoustic footprint, and the normalised acoustic footprint.

mmimpacts.m

This function will calculate the received levels (dB re 1 μPa RMS) and change in received levels (dB/min) from a vessel passage experienced by a marine mammal at a given closest point of approach distance.