Composite Training Unit Exercises and Joint Task ... - Govsupport.us

COMPTUEX/JTFEX EA/OEA Final Chapter 4μPa 2 -s is used to define the outer limit of the zone within which listed species are considered topotentially experience harassment attributable to behavioral effects without physiological effects.4.3.1.7.7 Criteria and Thresholds for Physiological EffectsThis section presents the effect criteria and thresholds for physiological effects of sound leading to injuryand behavioral disturbance. Previous sections identified the tissues of the ear as being the mostsusceptible to physiological effects of underwater sound. PTS and TTS were determined to be the mostappropriate biological indicators of physiological effects that equate to the onset of injury (Level Aharassment) and behavioral disturbance (Level B harassment), respectively. This section is, therefore,focused on criteria and thresholds to predict PTS and TTS in marine mammals.Marine mammal ears are functionally and structurally similar to terrestrial mammal ears; however, thereare important differences (Ketten, 2000). The most appropriate information from which to developPTS/TTS criteria for marine mammals would be experimental measurements of PTS and TTS frommarine mammal species of interest. TTS data exist for several marine mammal species and may be usedto develop meaningful TTS criteria and thresholds. PTS data do not exist for marine mammals and areunlikely to be obtained. Therefore, PTS criteria must be developed from TTS criteria and estimates of therelationship between TTS and PTS.This section begins with a review of the existing marine mammal TTS data. The review is followed by adiscussion of the relationship between TTS and PTS. The specific criteria and thresholds for TTS andPTS used in this authorization request are then presented. This is followed by discussions of soundenergy flux density level (EL), the relationship between EL and sound pressure level (SPL), and the useof SPL and EL in previous environmental compliance documents.Table 4.3-5. Energy Flux Density and Sound Pressure LevelsEnergy Flux Density Level and Sound Pressure LevelEnergy Flux Density Level (EL is the measure of sound energy flow per unit area expressed in dB. EL isstated in dB re 1 μPa 2 -s for underwater sound and dB re (20 μPa) 2 -s for airborne soundSound Pressure Level (SPL) is a measure of the root-mean square, or “effective,” sound pressure indecibels. SPL is expressed in dB re 1 μPa for underwater sound and dB re 20 μPa for airborne sound.TTS in Marine MammalsA number of investigators have measured TTS in marine mammals. These studies measured hearingthresholds in trained marine mammals before and after exposure to intense sounds. Some of the moreimportant data obtained from these studies are onset-TTS levels – exposure levels sufficient to cause ajust-measurable amount of TTS, often defined as 6 dB of TTS (for example, Schlundt et al., 2000). Theexisting cetacean TTS data are summarized in the following bullets.Schlundt, et al. (2000) reported the results of TTS experiments conducted with bottlenosedolphins and white whales exposed to 1-second tones. This paper also includes a reanalysisof preliminary TTS data released in a technical report by Ridgway et al. (1997). Atfrequencies of 3, 10, and 20 kHz (frequencies relevant to USWTR), SPLs necessary to inducemeasurable amounts (6 dB or more) of TTS were between 192 and 201 dB re 1 μPa (EL =192 to 201 dB re 1 μPa 2 -s). The mean exposure SPL and EL for onset-TTS were 195 dB re 1μPa and 195 dB re 1 μPa 2 -s, respectively. The sound exposure stimuli (tones) and relativelyFebruary 2007 4-26