Environmental compliance requirements regarding the potential impacts of noise on marine mammal populations creates a need to develop methods for assessing those impacts. Determining how marine mammals use and react to sound is of particular concern to the Department of Defense (DoD), because these animals have been reported to mass strand during naval exercises where sonar is used. Such determinations have proven challenging, as not knowing safe exposure levels to sonar for deep diving whales hinders assessments of the potential impact of Navy active acoustic operations on marine mammal behavior and prevents accurately estimating the potential number of “takes” resulting from such operations.
The objectives of this project were to (1) determine the feasibility of monitoring marine mammals in select Navy undersea ranges; (2) assess the availability, variability, and probability of detection and classification of the marine mammals; and (3) develop methods to determine the near- and long-term effects of Naval active acoustics on marine mammals in their natural ocean environment in select ocean areas of Navy interest.
A digital acoustic recording tag (DTAG) has been developed to measure the received level of stimulus at a whale while also measuring behavioral and physiological responses. The tag tracks responses of marine mammals (especially deep divers) throughout their dives. This information provides an improved understanding of the functions and costs of behaviors to infer the biological significance of behavioral disruption. Methods for attaching these tags have been tested on deep-diving beaked whales to prepare for studies of how they respond to carefully controlled exposures of man-made noise. Whales at multiple sites were tagged to estimate the probability of range sensors detecting their vocalizations.
Under SERDP Project RC-1539, follow-on research is under way to (1) ground truth acoustic monitoring on Navy ranges using boat-based observations and DTAGs; (2) develop tagging techniques and field efforts that use the DTAG to observe and monitor reactions of marine mammals to exposures of anthropogenic noise; (3) explore potential controlled exposure and opportunistic observation methods to evaluate safety zones based on beaked whale responses to sound; and (4) prepare a detailed plan for a research program to study the effects of multiple stimuli including experimental controls.
Data on behavioral reactions of deep-diving whales and other cetaceans to Navy noises make it possible to estimate the impact of naval operations on sea life. Vocalizations recorded point to a great potential for implementing passive acoustic detection of these species in important Navy undersea ranges and for developing monitoring and mitigation tools. (Project Completion - 2007)