Technical Acoustic Guidance FAQs
What is the purpose of the Technical Guidance?
The Technical Guidance provides acoustic thresholds for assessing the effects of anthropogenic sound on marine mammal species' hearing under NOAA Fisheries' jurisdiction. 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 Fisheries has presented acoustic thresholds for marine mammals in a single, comprehensive document in order to improve consistent implementation across the array of relevant laws that protect marine mammals.
What are the acoustic thresholds?
NOAA Fisheries has compiled, interpreted, and synthesized the best available science to produce updated acoustic thresholds for the onset of both temporary and permanent hearing threshold shifts. The acoustic thresholds in this document identify the levels of sound, which after they are exceeded, NOAA anticipates (after evaluating and interpreting all available science) changes in auditory sensitivity (temporary or permanent threshold shift).
It is important to note that the Technical Guidance's updated acoustic thresholds do not represent the entirety of an impact assessment, but rather serve as one tool to help evaluate the effects of a proposed action on marine mammals and make findings required by our various statutes.
Who should use the Guidance?
This Technical Guidance is intended to be used by NOAA analysts and managers, other federal agencies, and other relevant user groups and stakeholders to determine whether and how their activities are expected to result in particular types of impacts to marine mammals via acoustic exposure.
Activities with the greatest potential to affect marine mammals by noise include:
- Seismic airguns
- High-energy sonars (military)
- Explosive detonations
- Certain construction activities (impact pile driving)
What has changed between the Technical Guidance's acoustic thresholds and the thresholds NOAA Fisheries used to assess acoustic injury?
The Technical Guidance updates best available science, but does not change our regulatory application (e.g., issuing permits, conducting consultations, etc.) of these thresholds under relevant statutes (Marine Mammal Protection Act, Endangered Species Act, and National Marine Sanctuaries Act) which will remain consistent with past NOAA practice.
Before the Technical Guidance, acoustic thresholds consisted of a single threshold for cetaceans and a single threshold for pinnipeds regardless of sound source. They did not take into account the hearing ability of different marine mammal groups or the differences among sound sources in terms of auditory impacts.
The updated acoustic thresholds in the Technical Guidance consist of several thresholds that will replace those currently in use by NOAA Fisheries. These thresholds reflect the best available science on the potential for noise to affect auditory sensitivity by:
- Dividing sound sources into two groups based on their potential to affect hearing sensitivity:
- Impulsive sound sources (e.g., airguns, impact pile drivers): are transient, brief (less than 1 second), broadband, and typically consist of high peak pressure with rapid rise time and rapid decay, and based on these physical characteristics have a greater potential to affect hearing sensitivity
- Non-impulsive sound sources (e.g., sonar, vibratory pile drivers): can be broadband, narrowband or tonal, brief or prolonged, continuous or intermittent and typically do not have a high peak pressure with rapid rise time (typically only small fluctuations in dB level) that impulsive signals do
- Choosing metrics that better address the impacts of noise on hearing sensitivity:
- Peak sound pressure level: better reflects the physical properties of many sound sources, especially impulsive sources, to affect hearing sensitivity
- Cumulative sound exposure level: accounts for not only level of exposure but also duration of exposure
- Dividing marine mammals into functional hearing groups and developing auditory weighting functions based on the science supporting that not all marine mammals hear and use sound in the same manner (For reference, humans hear from 20Hz to 20kHz):
- Low-frequency cetaceans (hearing range 7 Hz to 35 kHz): large, baleen whale species
- Mid-frequency cetaceans (hearing range 150 Hz to 160 kHz): dolphin species
- High-frequency cetaceans (hearing range 275 Hz to 160 kHz): porpoise species
- Otariid pinnipeds (hearing range: 60 Hz to 39 kHz): eared seals (e.g., sea lions)
- Phocid pinnipeds (hearing range 50 Hz to 86 kHz): true/ earless seals (e.g., harbor seals)
NOAA recognizes that the acoustic thresholds in theTechnical Guidance are more complex than those previously used by applicants. We have added an appendix to the Technical Guidance that provides alternative methodology and tools to assist applicants in applying the more complex acoustic thresholds (Appendix D).
What do we know about the effects of anthropogenic noise on marine mammal hearing?
The Technical Guidance uses the best available science to develop our updated acoustic thresholds, understanding there is limited information available, especially from marine mammals in the wild. The data on hearing loss from noise exposure comes from laboratory studies on a few species (e.g., bottlenose dolphins, harbor porpoises, California sea lions, and harbor seals) and a limited number of individuals within those species. Where limited or no data are available, surrogate data from other marine mammal or terrestrial mammal species has been used. The thresholds will help identify data gaps and encourage further research.
How will application of the acoustic thresholds in the Technical Guidance compare to what NOAA has used previously?
Given the specific nature of the Technical Guidance's updates (e.g., different metrics, auditory weighting functions, etc.), it is not possible to directly compare the updated acoustic thresholds with the thresholds previously used by NOAA.
The updated acoustic thresholds are more complex than those previously used by NOAA. For example, the new thresholds include metrics for not only the level of exposure but also the duration of exposure, while the previous thresholds only account for level of exposures. Additionally, the updated acoustic thresholds take into account that not all marine mammals hear and use sound in the same way (i.e., functional hearing groups and auditory weighting functions), while previous thresholds only divided marine mammals into two basic groups (cetaceans and pinnipeds). NOAA Fisheries has added an appendix to the Technical Guidance that provides an optional methodology and tools to assist applicants and other members of the regulated community to apply the updated acoustic thresholds (Appendix D).
In some situations (e.g., depending on sound source, species, and duration of exposure), updated acoustic thresholds may result in more exposures than previously applied thresholds, while in others they may result in less exposures. However, these updated acoustic thresholds reflect the best available science on the potential for noise to affect auditory abilities of marine mammals.
Why are thresholds for behavioral response of marine mammals to sound not included in this document?
NOAA Fisheries is continuing our examination of the effects of noise on marine mammal behavior and will focus our work over the next years on developing guidance regarding the effects of anthropogenic sound on marine mammal behavior. Behavioral response is a complex question and one that requires additional time to research and address it appropriately.
What was the review process for the Technical Guidance?
The Technical Guidance is classified as a Highly Influential Scientific Assessment by the Office of Management and Budget. Independent peer review was required prior to broad public dissemination by the Federal Government. The Technical Guidance has undergone three independent peer reviews. To complete the review process for the Technical Guidance, NOAA Fisheries solicited input from stakeholders and the public via three public comment periods. More details on the review process are available on our website.
What was the process to address comments made during the first, second, and third public comment periods?
Before the Technical Guidance could be finalized, NOAA addressed all relevant and substantive public comments received from all three public comment periods. NOAA Fisheries published our responses to public comments in this Federal Register Notice.
When will the Technical Guidance be finalized and become effective?
NOAA Fisheries published our final Technical Guidance as a NOAA Technical Memorandum on July 29, 2016. NOAA Fisheries provides guidance on how applicants are expected to transition to implementing the Technical Guidance in this Federal Register Notice.
Updated: August 11, 2016