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

COMPTUEX/JTFEX EA/OEA Final Chapter 4 For pooled white whale and dolphin data at 3, 10, and 20 kHz, exposure SPLs of 180, 190, and199 dB re 1 μPa (ELs of 180, 190, and 199 dB re 1 μPa 2 -s) corresponded with the 25, 50, and75% altered behavior points, respectively.Navy Derivation of Effect ThresholdThe Navy supports a behavioral effects threshold based primarily on the behavioral observations reportedin Schlundt et al. (2000) and Finneran et al. (2000, 2003b, 2005). Finneran and Schlundt (2004)summarize these data and provide the statistical analysis used in development of this threshold. Thesestudies are applicable because they used short-duration tones and frequencies similar to the sonar usemodeled in this assessment. The most compelling reason for the use of this experimental data usingcaptive animals was the considerable number of studies involved and the absence of any other data usingrepresentative sound characteristics and experimental controls.The behavior of a subject during intense sound exposure experiments was subjectively compared to thesubject’s “normal” behaviors to determine whether a subject exhibited altered behavior during a session.In this context, altered behavior means a deviation from a subject’s typical trained behaviors. Thesubjective assessment was only possible because behavioral observations were made with the samesubjects during many baseline hearing sessions with no intense sound exposures. This allowedcomparisons to be made between how a subject usually acted and how it acted during test sessions withintense sound exposures. Each exposure session was then categorized as “normal behavior” or “alteredbehavior.” The behavioral alterations primarily consisted of reluctance on the part of the subjects, duringa test session, to return to the site of a previous intense sound exposure. All instances of altered behaviorwere included in the statistical summary. An example of the results is as follows: At 192 dB re 1 μPaexposure SPL, 7 of 13 white whale sessions and 16 of 32 dolphin sessions were categorized as alteredbehavior. The pooled percentage is therefore 51%, or 23 of 45 total sessions.Exposure levels corresponding to sessions with 25, 50, and 75% altered behavior were 180, 190, and 199dB re 1 μPa SPL (or 180, 190, and 199 dB re 1 μPa 2 -s EL), respectively. More detailed statistical resultsare provided in Finneran and Schlundt (2004).The use of the 50% point to estimate a single numeric “all-or-nothing” threshold from a psychometricfunction is a common and accepted psychophysical technique (e.g., Nachtigall, 2000; Yost, 1994). The50% altered point from these data is a conservative approach to predicting Level B harassment because itactually represents the sensory threshold point where the sound was strong enough to potentially result inaltered behavior 50% of the time; however, it may not result in significantly altered behavior as isrequired to be considered Level B harassment as defined for military readiness activities. Furthermore,Level B harassment for military readiness activities is defined as any act that disturbs or is likely todisturb a marine mammal indicating either a certainty of occurrence or that an occurrence is likely. It canbe argued that phenomena with occurrences below 50% are “not likely” since in the majority of the times,they by definition will not occur.Use of EL for Behavioral EffectsThe behavioral effect threshold is stated in terms of EL. If an animal is exposed to multiple pings, theenergy flux density in each individual ping is summed to calculate the total EL. EL is used for threereasons:EL takes both the exposure SPL and duration into account. Both SPL and duration ofexposure affect behavioral responses to sound, so a behavioral effect threshold must includeexposure duration. Use of SPL by itself in other effect scenarios relied on a known or fixedFebruary 2007 4-34