Marine mammals (whales, dolphins, seals, sea lions, sea cows) use sound both actively and passively to communicate and sense their environment, covering frequencies from a few hertz to greater than 100 kHz, differing with species. Although a few documents on marine mammal sound production and reception date back 200 years, concern about the effects of man-made noise on marine mammals has only been documented since the 1970s. Underwater noise can interfere with key life functions of marine mammals (e.g., foraging, mating, nursing, resting, migrating) by impairing hearing sensitivity, masking acoustic signals, eliciting behavioral responses, or causing physiological stress. Many countries are developing and updating guidelines and regulations for underwater noise management in relation to marine mammal conservation. In the United States, the Marine Mammal Protection Act, enacted in 1972, is increasingly being applied to underwater noise emission. Common mitigation methods include (1) time/area closures, (2) the establishment of safety zones that are monitored by visual observers or passive acoustics and that lead to shut-down or low-power operations if animals enter these zones, (3) noise reduction gear like bubble curtains around pile driving, and (4) noise source modifications or operational parameters like soft starts. Mitigation management mostly deals with single operations (like a one-month seismic survey). Key questions that remain are how noise impacts accumulate over time and multiple exposures, how multiple acoustic and nonacoustic stressors interact, and how effects on individuals affect a population as a whole.
This chapter is from the book Effects of Anthropogenic Noise on Animals.