This document provides voluntary 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 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 Technical Guidance may be used 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. Please note that action proponents have discretion as to whether to use the Technical Guidance; other scientifically rigorous methods are acceptable. This document outlines the development of NMFS’ thresholds and describes how they will be updated in the future.
NMFS has compiled, interpreted, and synthesized the scientific literature, including a 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 thresholds for onset of temporary (TTS) and permanent threshold shifts (PTS) (Table ES2). This document includes a protocol for estimating PTS onset 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 onset thresholds. These thresholds are presented using dual metrics of weighted cumulative sound exposure level (SELcum) and peak sound level (PK) for impulsive sounds and weighted SELcum for non-impulsive sounds.
While the Technical Guidance’s 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. NMFS recognizes that the implementation of marine mammal weighting functions and the weighted 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, Technical Guidance’s companion User Spreadsheet tool1, and recently developed User Spreadsheet Manual (NMFS 2018)1).
These 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. The Technical Guidance may inform decisions related to mitigation and monitoring requirements, but it does not mandate any specific mitigation be required. The Technical Guidance does not address or change NMFS’ application of these thresholds in the regulatory context, under applicable statutes and does not create or confer any rights for or on any person, or operate to bind the public. It only updates NMFS’ thresholds based on the most recent science.
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).