UC San Diego

Low-frequency (< 500 Hz) noise in the ocean is made up of natural abiotic sounds such as wind, biological sounds such as whale song, and anthropogenic noise such as sound radiated by ships (Wenz 1962; Hildebrand 2009). In areas exposed to commercial shipping, ship noise overtakes other sound sources in amplitude and is the dominant source of low-frequency noise. Over the past several decades, increases in the number, gross tonnage, and horsepower of commercial vessels have led to higher ambient sound levels in the ocean (McDonald, Hildebrand, and Wiggins 2006; Ross 2005). Sound travels extremely efficiently in the ocean and marine organisms use sound for vital life functions including communication, foraging, and mating (Simpson et al. 2008; Bass and McKibben 2003; Wartzok and Ketten 2014). Because of this, increases in anthropogenic noise have profound impacts on marine organisms (Weilgart 2018; Erbe et al. 2019). In Chapter 1, I partnered with a coalition of government agencies, non-profits, and environmental organizations to investigate an approach to noise reduction through incentive based vessel speed reduction. I share evidence for an operational approach to reducing the source level and sound exposure levels of vessels that participated voluntarily in the program. In Chapter 2, I collaborated with the largest container shipping company in the world, Maersk, to analyze changes in monopole source level and radiated noise level from a retrofitting initiative. I found that there were reductions below 100 Hz for monopole source levels post retrofitting. For Chapter 3, I trained a fully connected neural network to predict source levels when provided with a suite of automatic identification system information. In Chapter 4, I mapped sound pressure levels for modern and primeval times. I analyzed different approaches to reducing noise and simulated the sound pressure level across the region to identify the most effective techniques to reduce noise.