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

COMPTUEX/JTFEX EA/OEA Final Chapter 3Acoustics—Clicks with high repetition rates and whistles have been recorded from animals at sea (Fishand Turl, 1976; Leatherwood and Walker, 1979). Maximum source levels were approximately 170 dB 1Pa-m (Fish and Turl, 1976). There is no published data on the hearing abilities of this species.Pacific White-sided Dolphin (Lagenorhynchus obliquidens)Status—The Pacific white-sided dolphin is not listed under the ESA, and theCalifornia/Oregon/Washington Stock is not considered depleted or strategic under the MMPA. Nopopulation trends have been observed in California or adjacent waters. The best estimate of the size ofthe California/Oregon/Washington Stock, derived from data collected during shipboard surveysconducted between 1996 and 2001, is 39,822 (CV=0.50, Carretta et al., 2005).Distribution—There is conflicting evidence concerning seasonal shifts in distribution and numbers ofPacific white-sided dolphins in the Southern California Bight. Analyses of many years of data suggestthat peak numbers probably occur in and near the SOCAL Range Complex in the cold-water months(Leatherwood et al. 1984). Most wintertime Pacific white-sided dolphin sightings within the SCIRCoccurred in coastal waters on the western side of San Clemente Island (Carretta et al., 2000).The Pacific white-sided dolphin is most common in waters over the continental shelf and slope. Sightingrecords and captures in pelagic driftnets indicate that this species occurs in oceanic waters well beyondthe shelf and slope (Leatherwood et al., 1984; Ferreo and Walker, 1999). The Pacific white-sided dolphinoccurs across temperate Pacific waters, to latitudes as low as (or lower than) 38°N, and northward to theBering Sea and coastal areas of southeast Alaska (Leatherwood et al., 1984). Surveys suggest a seasonalnorth-south movement of Pacific white-sided dolphins in the eastern North Pacific, with animals foundprimarily off California during the colder water months and shifting northward into Oregon andWashington as water temperatures increase during late spring and summer (Green et al., 1992; Forney,1994; Carretta et al., 2005). Peak abundance in California waters occurs from November to April(Leatherwood et al., 1984). Pacific white-sided dolphins are found in the SOCAL OPAREA throughoutthe year (Carretta et al., 2005).Acoustics—Vocalizations produced by Pacific white-sided dolphins include whistles and clicks.Whistles are in the frequency range of 2 to 20 Hz (Richardson et al., 1995). Peak frequencies of the pulsetrains for echolocation fall between 50 and 80 kHz; the peak amplitude is 170 dB re 1Pa-m (Fahner etal., 2004). Tremel et al. (1998) measured the underwater hearing sensitivity of the Pacific white-sideddolphin from 75 Hz through 150 kHz. The greatest sensitivities were from 4 to 128 kHz, while the lowestmeasurable sensitivities were 145 dB at 100 Hz and 131 dB at 140 kHz. Below 8 Hz and above 100 kHz,this dolphin’s hearing was similar to that of other toothed whales.Pantropical Spotted Dolphin (Stenella attenuata)Status—The pantropical spotted dolphin is not listed as endangered under the ESA, and is not consideredto be a strategic stock under the MMPA. There are no abundance estimates available for this species inthe NOAA Stock Assessment Reports for this area of the Pacific.Distribution—The pantropical spotted dolphin can be found throughout tropical and some subtropicaloceans of the world (Perrin and Hohn, 1994). In the eastern Pacific, its range is from 25ºN (BajaCalifornia, Mexico) to 17ºS (southern Peru) (Perrin and Hohn, 1994). Pantropical spotted dolphins areassociated with warm tropical surface water (Au and Perryman, 1985; Reilly, 1990; Reilly and Fiedler,1994). Au and Perryman (1985) noted that the species occurs primarily north of the Equator, off southernMexico, and westward along 10ºN. They also noted its occurrence in seasonal tropical waters south ofthe Galápagos Islands.February 2007 3-50