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
195 dB. No fin whales would be exposed to received levels greater than 195 dB associated with these other training
activities.
Of the 1,712 instances in which <strong>NMFS</strong>’ exposure models identified fin whales that might be exposed to midfrequency
active sonar at received levels between 140 and 195 dB, about 1,002 of those instances would involve
exposures at received levels between 140 and 150 dB. Another 477 of those instances would involve exposures at
received levels between 150 and 160 dB. The balance of the exposures would occur at received levels greater than
160 dB.
As discussed in the Status of the Species section of this <strong>Opinion</strong>, fin whales produce a variety of low-frequency
sounds in the 10-200 Hz band (Watkins 1981; Watkins et al. 1987a; Edds 1988; Thompson et al. 1992). The most
typical signals are long, patterned sequences of short duration (0.5-2s) infrasonic pulses in the 18-35 Hz range
(Patterson and Hamilton 1964). Estimated source levels of their vocalizations reach as high as 190 dB (Patterson and
Hamilton 1964; Watkins et al. 1987a; Thompson et al. 1992; McDonald et al. 1995). In temperate waters intense
bouts of long patterned sounds are very common from fall through spring, but also occur to a lesser extent during the
summer in high latitude feeding areas (Clark and Charif 1998). Short sequences of rapid pulses in the 20-70 Hz band
are associated with animals in social groups (McDonald et al. 1995). Each pulse lasts on the order of one second and
contains twenty cycles (Tyack 1999). This information would lead us to conclude that fin whales exposed to these
received levels of active mid-frequency sonar are not likely to respond if they are exposed to mid-frequency (1 kHz–
10 kHz) sounds.
PROBABLE RESPONSE OF HUMPBACK WHALES. Because future Rim of the Pacific exercises occur in the Hawai’i
Range Complex in July when humpback whales do not occur in waters off Hawai’i, humpback whales would not be
exposed to the potential stressors associated with that exercise so the remainder of this discussions focuses on the
probable responses of humpback whales to activities the U.S. Navy plan to conduct in the Hawai'i Range Complex
each year from December 2008 through December 2013.
As discussed in our Exposure Analyses, we believe the estimates produced by our second and third exposure
scenarios are more likely to represent the number of instances in which humpback whales might be exposed to midfrequency
active sonar. The second scenario is more representative because it assumes that humpback whales are
most likely to avoid initial or continued exposure to active sonar. The third scenario is representative because it
captures patterns of abundance and migration by these whales in waters off the Hawai'ian Islands better than the
alternatives. However, both models are sensitive to our assumptions about the rate at which whale densities would
change in response to initial or continued exposure and when training activities would actually occur (that is, the
scenarios are sensitive to assumptions about whether they would be evenly distributed throughout the year, would
occur primarily during periods of low humpback whale density, or during periods of high humpback whale density).
Based on the information that is available, we would not expect humpback whales to be exposed to sound fields
produced by active sonar associated with all of the training exercises and other activities that would occur in the
Hawai'i Range Complex over the next five years. For example, monitoring surveys associated with the November
2007 Undersea Warfare Exercises did not report any sightings of humpback whales while monitoring surveys
associated with the March 2008 Undersea Warfare Exercises reported 40 sightings of 68 humpback whales during
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