UC San Diego

The extent to which low-frequency noise from large vessels is a part of the coastal marine environment and the ramifications of this for blue whale (Balaenoptera musculus) communication ranges and vocal behavior was investigated in the Santa Barbara Channel (SBC), a region off the coast of southern California. Analysis of noise from individual ships transiting the region, identified unique spectral characteristics, and radiated noise levels related to ship-type. Predicting radiated underwater noise from container ships under normal operating conditions proved to be challenging given the high dimensionality of the problem. Generalized additive models of radiated ship noise in relation to design characteristics, operational conditions, and oceanographic features revealed the most relevant parameters associated with ship noise. The statistical approach provided a comprehensive view of radiated ship noise in a coastal environment. Increased background noise levels from commercial ship traffic altered the low-frequency acoustic environment in which large whales are communicating. A comparison of long term averages of ambient noise at different sites revealed that blue whales utilizing this region are exposed to diverse acoustic environments and ranges at which they can communicate acoustically. A significant reduction in average noise levels in the SBC, related to changes in the economy and unintended consequences of an air quality improvement rule, was observed from 2007 to 2010. The decrease in ocean noise provided direct evidence for the impact on the ecosystem from the human activity and presented a unique opportunity to understand the magnitude of change necessary to improve the acoustic habitat quality for blue whales. Although the vocalizations of blue whales continued in the presence of ships, changes in call level and rate were observed. Understanding the interactions between human activity and the marine ecosystem is vital to its sustainability. The results of this research advance scientific understanding of human produced noise in the marine environment, and serves as a model for addressing noise pollution in a coastal region on both an ecosystem and individual species basis