This document provides technical guidance for assessing the effects of underwater anthropogenic (human-made) sound on the hearing of marine mammal species under the jurisdiction of the National Marine Fisheries Service (NMFS) and was completed in collaboration with the National Ocean Service (NOS), Office of National Marine Sanctuaries. Specifically, it identifies the received levels, or acoustic thresholds, at which individual marine mammals are predicted to experience changes in their hearing sensitivity (either temporary or permanent) for acute, incidental exposure to underwater anthropogenic sound sources. This is the first time NMFS has presented this information in a single, comprehensive document. This Technical Guidance is intended for use by NMFS analysts/managers and other relevant action proponents /stakeholders, including other federal agencies, when seeking to determine whether and how their activities are expected to result in potential impacts to marine mammal hearing via acoustic exposure. This document outlines the development of NMFS’ acoustic thresholds and describes how they will be updated in the future.
NMFS has compiled, interpreted, and synthesized the scientific literature, including a recent Technical Report by Dr. James Finneran (U.S. Navy-SPAWAR Systems Center Pacific (SSC-PAC)) (Finneran 2016; Appendix A of this Technical Guidance), to produce acoustic thresholds for onset of temporary (TTS) and permanent threshold shifts (PTS) (Table ES2) that update those currently in use by NMFS. Updates include a protocol for estimating PTS onset acoustic thresholds for impulsive (e.g., airguns, impact pile drivers) and non -impulsive (e.g., tactical sonar, vibratory pile drivers) sound sources, the formation of marine mammal hearing groups (low- (LF), mid- (MF), and high- (HF) frequency cetaceans, and otariid (OW) and phocid (PW) pinnipeds; Table ES1), and the incorporation of marine mammal auditory weighting functions (Figures ES1 and ES2) into the derivation of PTS acoustic thresholds. These acoustic thresholds are presented using dual metrics of cumulative sound exposure level (SELcum) and peak sound level ( PK ) for impulsive sounds and SEL cum for non -impulsive sounds.
While the Technical Guidance’s acoustic thresholds are more complex than those used to date in most cases by NMFS, they reflect the current state of scientific knowledge regarding the characteristics of sound that have the potential to impact marine mammal hearing sensitivity. Given the specific nature of these updates, it is not possible to generally or directly compare the updated acoustic thresholds presented in this document with the thresholds they will replace because outcomes will depend on project-specific specifications. NMFS recognizes that the implementation of marine mammal weighting functions and the SELcum metric represent new factors for consideration, which may extend beyond the capabilities of some action proponents. Thus, NMFS has developed alternative tools for those who cannot fully incorporate these factors (See Appendix D and Technical Guidance’s companion User Spreadsheet 1). These updated PTS acoustic thresholds do not represent the entirety of a comprehensive analysis of the effects of a proposed action, but rather serve as one tool (along with, e.g., behavioral impact thresholds, auditory masking assessments, evaluations to help understand the ultimate effects of any particular type of impact on an individual’s fitness, population assessments, etc.) to help evaluate the effects of a proposed action and make the relevant findings required by NOAA’s various statutes.
This Technical Guidance is classified as a Highly Influential Scientific Assessment (HISA) by the President’s Office of Management and Budget (OMB). As such, independent peer review was required prior to broad public dissemination by the Federal Government. Details of the three peer reviews, associated with the Technical Guidance, are within this document (Appendix C).
This document is organized so that the most pertinent information can be found easily in the main body. Additional details are provided in the appendices. Section I introduces the document. NMFS’ updated acoustic thresholds for onset of PTS for marine mammals exposed to underwater sound are presented in Section II. NMFS’ plan for periodically updating acoustic thresholds is presented in Section III. More details on the development of acoustic thresholds, the peer review and public comment process, research recommendations, alternative methodology, and a glossary of acoustic terms are found in the appendices.
The following Tables and Figures summarize the three main aspects of the Technical Guidance: 1) Marine mammal hearing groups (Table ES1), 2) Marine mammal auditory weighting functions (Figures ES1 and ES2 ; Table ES2), and PTS onset acoustic thresholds (Table ES3).