Expert Report

Each report is produced by a committee of experts selected by the Academy to address a particular statement of task and is subject to a rigorous, independent peer review; while the reports represent views of the committee, they also are endorsed by the Academy. Learn more on our expert consensus reports.

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

Key Messages

  • A conceptual model can assist in the understanding of acoustic disturbance of marine mammals and possible effects on populations of them. However, the paucity of data prevents such a model from having a predictive role now.
  • A conceptual model, such as the PCAD model, is useful for clarifying the complex problem of acoustic-disturbance effects on marine mammal populations. Such a model can be used as a framework for identifying the cause-effect relationships necessary for determining consequences of disturbances. Data to complete this exercise are lacking and must be pursued from every available source.
  • A wealth of data on marine mammals is collected in compliance with federal regulatory requirements. Such data are not collected in a manner that allows easy access or use beyond the original intent of their collection (such as permit issuance).
  • As opposed to the definition of biologically significant activities, whose disruption can constitute harassment, the crucial determination is of when behavioral or physiological responses result in deleterious effects on the individual animals and the population.
  • Continued development of more-sophisticated data logger tags is necessary to advance the study of marine mammal responses to anthropogenic sounds. Data logging packages should be modified to incorporate blood sampling during controlled-exposure experiments (CEEs).
  • Current knowledge is insufficient to predict which behavioral changes in response to anthropogenic sounds will result in significant population consequences for marine mammals.
  • Development of a model, such as the PCAD model, to inform regulatory decisions is critical for a full understanding of the biological significance of anthropogenic noise on marine mammal populations, but a more immediate solution is necessary.
  • During the last decade, the PBR mechanism has proved to be a successful model to account for the cumulative effects of lethal takes and serious injuries in commercial fisheries. However, as currently implemented, the PBR mechanism cannot adequately protect marine mammals from all sources of human-induced mortality until all such mortality is included in a revised and expanded PBR regime.
  • Focused effort is needed on a modeling exercise that should include demographic models, IBMs, and categorical modeling.
  • Measurements of glucocorticoids and other steroid hormone metabolites in terrestrial vertebrates have proved to be good indicators of pregnancy, allostatic overload, and mortality risk posed by current and new stressors.
  • Prior National Research Council reports (NRC, 1994, 2000, 2003b) identified high-priority subjects of research. The model proposed here requires the data and understanding that will become available on the fulfillment of the earlier National Research Council high-priority research recommendations.