Potential interactions between marine mammals and naval anthropogenic sound, principally sonar, are of concern to the Navy, regulatory agencies, environmental community, and general public. Behavioral response sets the threshold for noise exposures of concern, above which adverse effects to individuals may result in a regulatory take. The science challenges are first to be able to detect responses attributable to noise exposure and second to determine when these responses are biologically significant.  

SERDP and ESTCP worked with the Office of Naval Research, the Navy’s Environmental Readiness Division (N45), and the National Oceanic and Atmospheric Administration (NOAA) to develop a science plan that coordinates research efforts related to living marine resources, in particular marine mammals, and their response to naval anthropogenic sound. In the past, SERDP has funded efforts related to habitat and population modeling of marine mammals, as well as the development of advanced acoustic tags for recording animal behavior. Currently, the main contributions of SERDP and ESTCP are in the areas of improving understanding of baseline behavioral ecology of marine mammals of concern to the Navy and continued technology development to enhance the capability to collect behavioral and environmental data of interest.

To distinguish behavioral responses to anthropogenic sounds and to interpret the biological significance of any responses observed requires understanding baseline behavior—that is, how the animal behaves in its environment in the absence of anthropogenic sounds. Without such information, it would be difficult to identify, detect, and assess responses. Dose-response thresholds to anthropogenic sounds, if based on an erroneous understanding of a species’ behavioral ecology or on inadequate baseline data, may be set too conservatively and unnecessarily hinder training or too liberally and provide inadequate protection for species of concern.

Thresholds will likely differ by species, individual physiological and life history status, and environmental conditions. More specifically, the responses of animals may be influenced by (1) the age or sex of the animal, (2) its reproductive state, history of exposure, and motivation, (3) time of year, and (4) social conditions. Understanding the behavioral ecology of a species or taxonomic group is important for predicting the contexts when animals may be most sensitive to sound and for predicting when they may be most vulnerable to any potential adverse impacts. Over time the ability to stratify behavioral variance by age class, sex, animal condition, social situation, and season will further our understanding; however, such stratification will be difficult to achieve and may require research over long periods of time.

Finally, the marine environment and the manner in which cetaceans use marine habitat offer special challenges in obtaining the requisite information about exposure and response. In aquatic environments it is almost impossible to directly observe individual animals. As a result, animal-borne data loggers and passive acoustic monitoring technologies are crucial to studying the eco-physiology and biomechanics of animals under natural conditions. Bio-logging and acoustic monitoring lie at the interface between scientific inquiry and technological feasibility. Improvements have occurred in data loggers that incorporate increased memory capacity with the availability of new sensors, methods of data recovery, and techniques for data analysis. Additional advances are needed, however, to improve the quantity and quality of data collection and its efficient transmission and processing. SERDP and ESTCP continue to develop new technologies and then demonstrate and validate their performance and cost.