Behavioral Response Research Review

Research on behavioral responses of marine mammals to naval sonar exposure has been funded by US and European Navies for around two decades. We review and synthesize the scientific questions that have been addressed through Behavioral Response Studies (BRSs), the data generated, and the analysis methods used. With help from BRS researchers, we assembled a database of 137 documents and more than 4,300 exposure events on 30 species. Of the exposures, 28% were from experimental studies (i.e., controlled exposure experiments, CEEs) on captive animals, 16% were from CEEs on free-ranging animals and 56% from observational studies on free-ranging animals. In studies of free-ranging animals, there was a strong emphasis on beaked whales: almost 2,000 exposures were recorded across both CEEs and observational studies, with 41 different analyses conducted, mostly focusing on detecting responses that may be interpreted as foraging disruption. To our knowledge, there have been
no free-ranging sonar exposure studies to date on pinnipeds. We further decompose studies into sonar source type, study location (on-, near- or off-range), source vessel (research vs. operational Navy), duration of exposure, as well as a range of other contextual variables. A variety of scientific questions have been addressed, but the focus of most analyses has been on determining whether a response occurred and establishing relationships between response
and variables related to sonar exposure and other contextual variables. Eighty-one percent of studies reported evidence of a response, although this was higher for CEEs than observational studies. We highlight some gaps in taxa studied, response types analyzed, and methods for analyzing data. We also discuss how the data collected has been used by the Navy to underpin the behavioral response functions used by the US Navy in their Phase 4 Criteria and
Thresholds for Acoustic and Explosive Effects Analysis. Of the 4,300 exposure events, 83% have been included in publications or reports. There is now a large quantity of BRS exposure data across many species and contexts, representing a valuable resource for the Navy. Potential next steps include: a gap analysis specific to Navy needs, consideration of whether data may be combined to help address outstanding questions, and a synthesis of the biological findings across studies, taxa, sound sources, and other contexts.