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

COMPTUEX/JTFEX EA/OEA Final Chapter 3Temporary threshold shifts (TTS) in hearing have been experimentally induced in captive bottlenosedolphins (Ridgway et al., 1997; Schlundt et al., 2000; Nachtigall et al., 2003). Ridgway et al. (1997)observed changes in behavior at the following minimum levels for 1 sec tones: 186 dB at 3 kHz, 181 dBat 20 kHz, and 178 dB at 75 kHz (all re 1 Pa-m). TTS levels were 194 to 201 dB at 3 kHz, 193 to 196dB at 20 kHz, and 192 to 194 dB at 75 kHz (all re 1 Pa-m). Schlundt et al. (2000) exposed bottlenosedolphins to intense tones (0.4, 3, 10, 20, and 75 kHz); the animals demonstrated altered behavior at sourcelevels of 178 to 193 dB re 1 Pa-m, with TTS after exposures generally between 192 and 201 dB re 1Pa-m (though one dolphin exhibited TTS after exposure at 182 dB re 1 Pa-m). Nachtigall et al. (2003)determined threshold for a 7.5 kHz pure tone stimulus. No shifts were observed at 165 or 171 dB re 1Pa-m, but when the noise level reached 179 dB re 1 Pa-m, the animal showed the first sign of TTS.Recovery apparently occurred rapidly, with full recovery apparently within 45 min following noiseexposure. TTS measured between 8 and 16 kHz (negligible or absent at higher frequencies) after 30 minof noise exposure (4 to 11 kHz) at 160 dB re 1 Pa-m (Nachtigall et al., 2004).Bottlenose Dolphin, Offshore Stock (Tursiops truncatus)Status—Bottlenose dolphins are not listed as endangered under the ESA, and theCalifornia/Oregon/Washington Stock is not considered to be depleted or strategic under the MMPA. Theminimum population estimate for the California/Oregon/Washington Stock is 5,065 (CV=0.66)individuals (Carretta et al., 2005).Distribution—Offshore bottlenose dolphins are thought to have a continuous distribution in California(Mangels and Gerrodette, 1994). They have been found in the Southern California Bight and in waters asfar north as ~41ºN (Barlow et al., 1997). During most of the year, a relatively large population ofbottlenose dolphins occurs in offshore waters of the Southern California Bight centered around SantaCatalina Island and, to a lesser degree, the eastern coast of San Clemente Island. The population maydisperse more broadly in summer than in winter (Dohl et al., 1981). Offshore bottlenose dolphins arefound in the SOCAL OPAREA throughout the year (Carretta et al., 2005).Acoustics—The acoustic abilities of offshore bottlenose dolphins is assume to be similar to the coastalpopulation of bottlenose dolphins described in the previous section on the coastal stock of bottlenosedolphins.Cuvier’s Beaked Whale (Ziphius cavirostris)Status—The Cuvier’s beaked whale is not listed as endangered under the ESA, and theCalifornia/Oregon/Washington Stock is not considered to be strategic under the MMPA. The minimumpopulation estimate for the California/Oregon/Washington Stock is 1,121 (CV=0.68) individuals (Carrettaet al., 2005).Distribution—Little is known about the habitat preferences of any beaked whale. Based on currentknowledge, beaked whales normally inhabit deep ocean waters (>2,000 m) or continental slopes (200–2,000 m), and only rarely stray over the continental shelf (Pitman, 2002). Cuvier’s beaked whalegenerally is sighted in waters >200 m deep, and is frequently recorded at depths >1,000 m (Gannier,2000; MacLeod et al., 2004). They are commonly sighted around seamounts, escarpments, and canyons.MacLeod et al. (2004) reported that Cuvier’s beaked whales occur in deeper waters than Blainville’sbeaked whales in the Bahamas.The distribution and abundance of beaked whales in the SOCAL Range Complex are not well knownbecause they are difficult to identify; many of the beaked whales that have been sighted have not beenidentified to species. Based on those that were identified, Cuvier’s beaked whale appears to be the most3-43 February 2007