This volume reviews the current state of knowledge regarding the effects of low-frequency sound on marine mammals and makes recommendations for research. In addition, the book describes current federal regulations prescribed under the Marine Mammal Protection Act that govern the taking of marine mammals by scientific research activities, and it recommends changes to expedite the regulatory process dealing with scientific research activities.

Many marine mammals communicate by emitting sounds that pass through water. Such sounds can be received across great distances and can influence the behavior of these undersea creatures. In the past few decades, the oceans have become increasingly noisy, as underwater sounds from propellers, sonars, and other human activities make it difficult for marine mammals to communicate. This book discusses, among many other topics, just how well marine mammals hear, how noisy the oceans have become, and what effects these new sounds have on marine mammals. The baseline of ambient noise, the sounds produced by machines and mammals, the sensitivity of marine mammal hearing, and the reactions of marine mammals are also examined. An essential addition to any marine biologist's library, Marine Mammals and Noise will be especially appealing to marine mammalogists, researchers, policy makers and regulators, and marine biologists and oceanographers using sound in their research.

For the 119 species of marine mammals, as well as for some other aquatic animals, sound is the primary means of learning about the environment and of communicating, navigating, and foraging. The possibility that human-generated noise could harm marine mammals or significantly interfere with their normal activities is an issue of increasing concern. Noise and its potential impacts have been regulated since the passage of the Marine Mammal Protection Act of 1972. Public awareness of the issue escalated in 1990s when researchers began using high-intensity sound to measure ocean climate changes. More recently, the stranding of beaked whales in proximity to Navy sonar use has again put the issue in the spotlight. Ocean Noise and Marine Mammals reviews sources of noise in the ocean environment, what is known of the responses of marine mammals to acoustic disturbance, and what models exist for describing ocean noise and marine mammal responses. Recommendations are made for future data gathering efforts, studies of marine mammal behavior and physiology, and modeling efforts necessary to determine what the long- and short-term impacts of ocean noise on marine mammals.

Marine mammals face a large array of stressors, including loss of habitat, chemical and noise pollution, and bycatch in fishing, which alone kills hundreds of thousands of marine mammals per year globally. To discern the factors contributing to population trends, scientists must consider the full complement of threats faced by marine mammals. Once populations or ecosystems are found to be at risk of adverse impacts, it is critical to decide which combination of stressors to reduce to bring the population or ecosystem into a more favorable state. Assessing all stressors facing a marine mammal population also provides the environmental context for evaluating whether an additional activity could threaten it. Approaches to Understanding the Cumulative Effects of Stressors on Marine Mammals builds upon previous reports to assess current methodologies used for evaluating cumulative effects and identify new approaches that could improve these assessments. This review focuses on ways to quantify exposure-related changes in the behavior, health, or body condition of individual marine mammals and makes recommendations for future research initiatives.

Attention has been drawn to the subject of how ocean noise affects marine mammals by a series of marine mammal strandings, lawsuits, and legislative hearings, and most recently, the report from the U.S. Commission on Ocean Policy. One way to assess the impact of ocean noise is to consider whether it causes changes in animal behavior that are "biologically significant," that is, those that affect an animal's ability to grow, survive, and reproduce. This report offers a conceptual model designed to clarify which marine mammal behaviors are biologically significant for conservation purposes. The report is intended to help scientists and policymakers interpret provisions of the federal Marine Mammal Protection Act.

Sound has become a major tool for studying the ocean. Although the ocean is relatively opaque to light, it is relatively transparent to sound. Sound having frequencies below 1,000 Hertz (Hz) is often defined as low-frequency sound. The speed of sound is proportional to the temperature of the water through which it passes. Therefore, sound speed can be used to infer the average temperature of the water volume through which sound waves have passed. The relationship between water temperature and the speed of sound is the basis for the Acoustic Thermometry of Ocean Climate (ATOC) experiment. The ATOC experiment is designed to monitor the travel time of sound between sources off the coasts of Hawaii and California and several receivers around the Pacific Ocean in order to detect trends in ocean temperature and for other research and monitoring purposes. Some whales, seals, and fish use low-frequency sound to communicate and to sense their environments. For example, baleen whales and some toothed whales are known to use and respond to low-frequency sound emitted by other individuals of their species. Sharks are not known to produce low-frequency sound but are attracted to pulsed low-frequency sounds. Therefore, it is possible that human-generated low-frequency sound could interfere with the natural behavior of whales, sharks, and some other marine animals. Marine Mammals and Low-Frequency Sound is an updated review of the National Research Council 1994 report Low-Frequency Sound and Marine Mammals: Current Knowledge and Research Needs, based on data obtained from the MMRP and results of any other relevant research, including ONR's research program in low-frequency sound and marine mammals. This report compares new data with the research needs specified in the 1994 NRC report, focusing on the strengths and weaknesses of the data for answering important outstanding questions about marine mammal responses to low-frequency sound and identifies areas where gaps in our knowledge continue to exist.