Draft Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammals: Acoustic Threshold Levels for Onset of Permanent and Temporary Threshold Shifts


Title: Draft Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammals: Acoustic Threshold Levels for Onset of Permanent and Temporary Threshold Shifts
Publication Date:
December 23, 2013
Pages: 83

Document Access

Website: External Link
Attachment: Access File
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National Oceanic and Atmospheric Administration (2013). Draft Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammals: Acoustic Threshold Levels for Onset of Permanent and Temporary Threshold Shifts. Report by National Marine Fisheries Service (NMFS) and National Oceanic and Atmospheric Administration (NOAA). pp 83.

This document provides guidance for assessing the effects of anthropogenic sound on marine mammal species under the jurisdiction of the National Marine Fisheries Service (NMFS) and the National Ocean Service (NOS) (hereafter referred to collectively as the National Oceanic and Atmospheric Administration (NOAA)). Specifically, it identifies the received levels, or thresholds, above which individual marine mammals are predicted to experience changes in their hearing sensitivity (either temporary or permanent) for all underwater anthropogenic sound sources. This is the first time NOAA has presented this information in a single, comprehensive document. This guidance is intended to be used by NOAA analysts and managers and other relevant user groups and stakeholders, including other federal agencies, when seeking to determine whether and how their activities are expected to result in particular types of impacts to marine mammals via acoustic exposure. This document outline s NOAA’s updated acoustic threshold levels and describes in detail how the thresholds were developed and how they will be updated in the future.


NOAA has compiled, interpreted, and synthesized the best available science to produce updated acoustic thresh old levels for the onset of both temporary (TTS) and permanent hearing threshold shifts (PTS). These thresholds replace those currently in use by NOAA. Updates include a protocol for estimating PTS and TTS onset levels for impulsive (e.g., airguns, impact pile drivers) and non-impulsive (e.g., sonar, vibratory pile drivers) sound sources, the formation of marine mammal functional hearing groups (low-, mid-, and high-frequency cetaceans, and otariid and phocid pinnipeds), and the incorporation of marine mammal auditory weighting functions into the calculation of thresholds. These acoustic threshold levels are presented using the dual metrics of cumulative sound exposure level and peak sound pressure level. This document addresses how to combine multiple datasets, as well as how to determine appropriate surrogates when data are not available. While the updated acoustic thresholds are more complex than those previously used by NOAA, they accurately 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 directly compare the updated thresholds presented in this document with the thresholds previously used by NOAA.


Although NOAA has updated the acoustic threshold levels from those previously used, and these changes may necessitate new methodologies for calculating impacts, the application of the thresholds in the regulatory context under applicable statutes (Marine Mammal Protection Act, Endangered Species Act, and National Marine Sanctuaries Act) remains consistent with past NOAA practice. It is important to note that these updated acoustic threshold levels do not represent the entirety of an impact assessment, but rather serve as one tool (in addition to 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 on marine mammals and make findings required by our various statutes.


This acoustic guidance is classified as a Highly Influential Scientific Assessment by the Office of Management and Budget. As such, independent peer review is required prior to broad public dissemination by the Federal Government. Details of the peer review can be found within this document, and at the following website: http://www.nmfs.noaa.gov/pr/acoustics/.


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 provides an introduction to the document and a description of how NOAA addressed uncertainty and data limitations in the development of this guidance. NOAA’s updated acoustic threshold levels for onset of PTS and TTS for marine mammals exposed to underwater sound are presented in Section II. Section III describes how acoustic threshold levels are interpreted under NOAA’s statutes. NOAA’s plan for periodically updating acoustic threshold levels is presented in Section IV. More details on the marine mammal auditory weighting functions, the development of acoustic threshold levels, the peer review process, and a glossary of acoustic terms can be found in the appendices.

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