NMFS Biological Opinion on U.S. Navy training ... - Govsupport.us

FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013
The outer ear is separated from the inner ear by the tympanic membrane, or eardrum. In terrestrial mammals, the
outer ear, eardrum, and middle ear function to transmit airborne sound to the inner ear, where the sound is detected
in a fluid. Since cetaceans already live in a fluid medium, they do not require this matching, and thus do not have an
air-filled external ear canal. The inner ear is where sound energy is converted into neural signals that are transmitted
to the central nervous system via the auditory nerve. Acoustic energy causes the basilar membrane in the cochlea to
vibrate. Sensory cells at different positions along the basilar membrane are excited by different frequencies of sound
(Tyack 1999). Baleen whales have inner ears that appear to be specialized for low-frequency hearing. In a study of
the morphology of the mysticete auditory apparatus, Ketten (1997) hypothesized that large mysticetes have acute
infrasonic hearing.
3.3.2 Humpback Whale
Distribution
Humpback whales are a cosmopolitan species that occur in the Atlantic, Indian, Pacific, and Southern Oceans.
Humpback whales migrate seasonally between warmer, tropical or sub-tropical waters in winter months (where they
reproduce and give birth to calves) and cooler, temperate or sub-Arctic waters in summer months (where they feed).
In their summer foraging areas and winter calving areas, humpback whales tend to occupy shallower, coastal waters;
during their seasonal migrations, however, humpback whales disperse widely in deep, pelagic waters and tend to
avoid shallower coastal waters (Winn and Reichley 1985).
In the North Pacific Ocean, the summer range of humpback whales includes coastal and inland waters from Point
Conception, California, north to the Gulf of Alaska and the Bering Sea, and west along the Aleutian Islands to the
Kamchatka Peninsula and into the Sea of Okhotsk (Tomlin 1967, Nemoto 1957, Johnson and Wolman 1984 as cited
in <strong>NMFS</strong> 1991b). These whales migrate to Hawai'i, southern Japan, the Mariana Islands, and Mexico during the
winter.
In the Atlantic Ocean, humpback whales range from the mid-Atlantic bight, the Gulf of Maine, across the southern
coast of Greenland and Iceland, and along coast of Norway in the Barents Sea. These humpback whales migrate to
the western coast of Africa and the Caribbean Sea during the winter.
In the Southern Ocean, humpback whales occur in waters off Antarctica. These whales migrate to the waters off
Venezuela, Brazil, southern Africa, western and eastern Australia, New Zealand, and islands in the southwest Pacific
during the austral winter. A separate population of humpback whales appears to reside in the Arabian Sea in the
Indian Ocean off the coasts of Oman, Pakistan, and India (Mikhalev 1997).
Population Structure
Descriptions of the population structure of humpback whales differ depending on whether an author focuses on
where humpback whales winter or where they feed. During winter months in northern or southern hemispheres, adult
humpback whales migrate to specific areas in warmer, tropical waters to reproduce and give birth to calves. During
summer months, humpback whales migrate to specific areas in northern temperate or sub-arctic waters to forage. In
summer months, humpback whales from different “reproductive areas” will congregate to feed; in the winter months,
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