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

COMPTUEX/JTFEX EA/OEA Final Chapter 44.3.1.7.9 Application of Effect Thresholds to Beaked WhalesRecent beaked whale strandings have prompted inquiry into the relationship between high-amplitudecontinuous-type sound and the cause of those strandings. In the one stranding where U.S. Navy midfrequencysonar has been identified as the most plausible contributory source to the stranding event, theNavy participated in an extensive investigation of the stranding with NMFS.The Navy analyzed the known range of operational, biological, and environmental factors involved in theBahamas stranding and focused on the interplay of these factors to reduce risks to beaked whales fromASW training operations. Consequently, the planned use and location in which COMPTUEX/JTFEXASW would occur would maximize both training fidelity (readiness) and the protection of beaked whales.The Bahamas exercise entailed multiple ships using mid-frequency active sonar during transits of aconstricted channel. COMPTUEX/JTFEX ASW activities within the SOCAL OPAREA differ from thecircumstances surrounding the Bahamas stranding because the SOCAL OPAREA does not have thecombination of environmental conditions most likely to have contributed to the stranding.In contrast to the Bahamas exercise, the COMPTUEX/JTFEX training events involving multiple surfaceships and would not include multiple transits across a constricted channel. Additionally, the nominalsource level for COMPTUEX/JTFEX training would be limited to 235 dB re 1Pa 2 -s @ 1 m for the SQS-53C.A review of stranding incidents and ASW training practices has led the Navy to conclude that theproposed nominal source levels for training activities taking place during COMPTUEX/JTFEX wouldreduce possible effects to marine mammals while providing training realism. From a tactical perspective,higher source levels for shallow water ASW increase the likelihood of detection by enemy submarinesand the amount of reverberation (reflections), which negatively impacts the ability to detect enemysubmarines.The interaction of unique environmental factors involved in the Bahamas and at the sites of other beakedwhale stranding events are not present in the SOCAL OPAREA. The “Joint Interim Report, BahamasMarine Mammal Stranding Event of 15-16 March 2000” (Department of Commerce [DOC] and U.S.Navy, 2001) concluded that environmental and biological factors, including the presence of a strongsurface duct, unusual underwater bathymetry, a constricted channel with limited egress, and the presenceof beaked whales were contributory factors to the stranding. Beaked whales are expected in the deeperportions of the SOCAL OPAREA; however, the combination of environmental factors contributing to theBahamas stranding event is not present in the SOCAL OPAREA.Since the exact causes of the stranding events are unknown, separate, meaningful impact thresholdscannot be derived specifically for beaked whales. The Navy, in consideration of the repetitive use of midfrequencysonar proposed for USWTR operations on the east coast, took a conservative approach andtreated all behavioral disturbances of beaked whales as a potential injury. All predicted Level Bexposures of beaked whales were counted as non-lethal Level A exposures.4.3.1.7.10 Active Acoustic Source DescriptionsThis section describes the active acoustic sources that could be associated with each training platform(aircraft, ships, submarines, etc.) during COMPTUEX and JTFEX. When selecting the sonar systems tomodel, several considerations were factored:Although the AN/AQS 13 dipping sonar is still in use, it is being replaced with a newer system,the AN/AQS-22, and therefore, the newer was modeled.February 2007 4-36