Expert Report

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For the 119 species of marine mammals, as well as for some other aquatic animals, sound is the primary means of learning about their environment and of communicating, navigating, and foraging. Ambient noise and its potential impacts have been regulated since the passage of the Marine Mammal Protection Act of 1972; however, public awareness of the issue has escalated in the past decade when researchers began using high-intensity sound to measure ocean climate changes and stranding of beaked whales occurred in proximity to U.S. Navy sonar use. This report 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.

Key Messages

  • Addressing the challenge of both short- and long-term effects of ocean noise on marine mammals is a difficult problem and will require a multidisciplinary effort between biologists and acousticians to establish a rigorous observational, theoretical, and modeling program.
  • Although the few documented cases of direct impact on individuals have raised awareness of potential population impacts, no measures exist of marine mammal population effects from ocean noise.
  • Currently, data regarding noise produced by shipping, seismic surveying, oil and gas production, marine and coastal construction, and other marine activities are either not known or are difficult to analyze because they are maintained by separate organizations such as industry database companies, shipping industry groups, and military organizations.
  • Each characteristic of noise from anthropogenic sources may differentially impact each species of marine mammals. The complex interactions of sound with marine life are not sufficiently understood to specify which features of the acoustic signal are important for specific impacts. Therefore as many as characteristics as possible should be measured and reported.
  • Efforts must be made to measure ocean noise in marine mammal habitats. Until these habitats are fully known and described, it is reasonable to begin a long-term monitoring program in coastal areas and areas close to known marine mammal foraging, migration, and breeding areas.
  • Federal leadership is needed to (1) monitor ocean noise, especially in areas with resident marine mammal populations; (2) collect and analyze existing databases of marine activity; and (3) coordinate research efforts to determine long-term trends in marine noise and the possible consequences for marine life.
  • Fish use sound in many ways that are comparable to the ways marine mammals communicate and sense their environment. The effects of anthropogenic noise on fishes and other nonmammalian species, including their eggs and larvae, are largely unknown.
  • Identifying reliable indicators for anthropogenic sources will provide an additional modeling tool and predictive capability that will be particularly useful in areas where long-term monitoring may be difficult or impossible.
  • Little is known about long-term trends in ocean noise levels.
  • Marine mammals themselves may be significant sources of ocean noise, although possibly in localized areas over limited time periods.
  • Short-term responses of marine mammals to anthropogenic noise sources have been documented to a limited degree; however, long-term effects of marine noise on the behavior of marine mammals have received less attention.
  • Simulation models that predict the characteristics of the noise (frequency content, mean squared level, peak level, pressure time series, etc.) and their effects on marine mammals may assist in understanding and mitigating harmful effects of marine noise on mammals.
  • Stress indicators may be one useful marker for long-term effects of anthropogenic noise on marine mammals.
  • There is a surprising lack of information regarding the global distribution of marine mammals. Migration routes, breeding grounds, and feeding areas are known for relatively few species.
  • There is an indirect relationship between strandings and the use of multiple mid-range sonars in military exercises in some nearshore beaked whale habitats.
  • Two technological improvements of current tags are needed: (1) increase the duration of long-term data-gathering tags from months to multiple years to observe annual behavior cycles and migration patterns, and (2) extend the duration of high-resolution tags from hours to days to gather more data on daily behavior and environmental cues.