NMFS Discusses Behavioral Effects Thresholds in IHA

The U.S. National Marine Fisheries Service has issued an Incidental Harassment Authorization to Bay State Wind LLC to take marine mammals, by harassment, incidental to high-resolution geophysical and geotechnical survey investigations associated with marine site characterization activities off the coast of Massachusetts in the area of the Commercial Lease of Submerged Lands for Renewable Energy Development on the Outer Continental. This IHA is effective August 13, 2016, through August 12, 2017.

NMFS continues to use 160 dB as the effects threshold for behavioral effects, and the IHA includes some discussion of NMFS’ current thinking on behavioral effects.  NMFS states in response to Marine Mammal Commission comments:

“The Commission recommended that until behavior thresholds are updated, that NMFS require applicants to use the 120-dB rather than 160-dB Level B harassment threshold for sub-bottom profilers. The Commission has made similar comments on other NMFS authorizations (e.g., ExxonMobil Alaska liquefied natural gas geophysical surveys; NMFS Fisheries Science Center fisheries research) proposed for activities using acoustic non-impulsive sources, including sub-bottom profilers, echosounders, and other sonars (e.g., side scan and fish-finding).”

“Response….  The 120-dB threshold is typically associated with continuous sources. Continuous sounds are those whose sound pressure level remains above that of the ambient sound, with negligibly small fluctuations in level (NIOSH 1998; ANSI 2005). Intermittent sounds are defined as sounds with interrupted levels of low or no sound (NIOSH 1998).”


“NMFS agrees with the Commission’s recommendation to update existing acoustic criteria and thresholds as necessary to specify threshold levels that would be more appropriate for a wider range of sound sources, and is currently in the process of producing such revisions. In particular, NMFS recognizes the importance of context (e.g., behavioral state of the animals, distance) in behavioral responses. The current behavioral categorization (i.e., impulse vs. continuous) does not account for context and is not appropriate for all sound sources. Thus, updated NMFS Acoustic Guidance (http://www.nmfs.noaa.gov/pr/ acoustics/guidelines.htm), once finalized, will more appropriately categorize behavioral harassment criteria by activity type. NMFS recognizes, as new science becomes available, that our current categorizations (i.e., impulse vs. continuous) may not fully encompass the complexity associated with behavioral responses (i.e., context, etc.) and are working toward addressing these issues in future acoustic guidance. However, in the meanwhile, while our current behavioral acoustic thresholds may not fully account for some of the differences observed across taxa and contexts, they still serve as somewhat conservative generalized indicators of received levels at which we anticipate behavioral harassment, and are not undermined by newer information.”

Click here to read NMFS’ Federal Register notice of this IHA.

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