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
given that they have been exposed and respond to that exposure” versus “number of times marine mammals might be
exposed”).
1. THE U.S. NAVY’S “TAKE” ESTIMATES FOR THE 2006 RIM OF THE PACIFIC EXERCISE. To estimate the number of
marine mammals that were likely to be “taken” as a result of their exposure to mid-frequency active sonar during the
2006 Rim of the Pacific exercise, the U.S. Navy developed and ran computer simulations that made several
assumptions about marine mammals in the Hawai’i Range Complex (U.S. Navy 2006; see Appendix C of that
document for a more detailed presentation of the Navy’s modeling procedures):
1. acoustic energy would be constant throughout the vertical water column at a given horizontal range from
the source;
2. marine mammal hearing is omni-directional;
3. marine mammals were static (not moving) at the maximum acoustic energy depth at any range.
The Navy’s models assumed ship speeds of 10 knots for all exercises except those taking place in Area 4 where
speeds were modeled at 20 knots. All active sonar was modeled using the operational characteristics of the AN/SQS-
53 and its variants.
The model the Navy used in 2006 included several other considerations or assumptions about marine mammals.
First, the model considered the density and hearing of marine mammals, but did not attempt to predict an animal’s
location relative to the point where active sonar transmissions began or the animal’s behavioral response to sound in
the water. That is, the model assumed that marine mammals would not leave an area once they were exposed to
active sonar transmissions. Second, the model assumed that mammals would be exposed to the maximum received
levels calculated for the horizontal distance to the source at any water depth for that distance although direct path
sound transmission was not always likely. Both of these assumptions — assuming that marine mammals are not
likely to try to avoid exposure or continued exposure to active sonar and that they would be exposed to the maximum
received levels calculated for the horizontal distance to a sound source — would tend to overestimate the number of
marine mammals that might be exposed, because marine mammals are highly mobile and are likely to use their
mobility to avoid stimuli like active sonar, just as they avoid vessel traffic. Consequently, the results of this approach
would be conservative, in the sense that they would tend to overestimate the number of animals that were likely to
have been “taken” during the 2006 Rim of the Pacific Exercise.
2. U.S. NAVY EXPOSURE ESTIMATES FOR PROPOSED ACTIONS IN THE HAWAI'I RANGE COMPLEX. Over the past
year, the U.S. Navy updated its approach to estimating the number of marine mammals that might be exposed to the
activities the U.S. Navy plans to conduct in the Hawai’i Range Complex over the five-year period beginning in
January 2009. What follows is a brief summary of the Navy’s current approach (for more details, refer to Appendix
K of the U.S. Navy’s Environmental Impact Statement — draft or final — on the Hawai'i Range Complex; U.S.
Navy 2007 and 2008a).
The U.S. Navy’s updated approach focuses on a suite of representative provinces based on sound velocity profiles,
bathymetries, and bottom types. Within each of these provinces, the U.S. Navy modeled transmission losses in 5
meter increments and used the results to build sound fields (based on maximum sound pressure levels). The U.S.
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