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
for Hawai’ian monk seals), or the amount of time a marine mammal would not occur in a “sonar shadow” created by
one of the islands (for example, humpback whales that occur in the Maui basin). The results of this model are
comparable to exposure estimates groups such as the Lamont-Doherty Earth Observatory and LGL Environmental
Research Associates use to estimate the number of marine mammals that might be exposed during seismic surveys.
As discussed in the Approach to the Assessment section of this <strong>Opinion</strong>, we used this equation to model three
separate exposure scenarios:
1. a scenario that assumed that marine mammal densities never changed and that individual animals did not
move during the course of an exercise (this is the closest approximation of the U.S. Navy’s and the Permits
Division’s models), which we conducted for all endangered and threatened marine mammals;
2 a scenario that assumed that marine mammals would, in fact, try to avoid exposure to active sonar
transmissions (for a review of literature supporting this assumption, see Behavioral Avoidance in the
Response Analyses that we present later in this <strong>Opinion</strong>). This scenario assumed that marine mammals
would avoid being exposed to higher received levels of active sonar (received levels greater than 195 dB) at
a faster rate than they would avoid lower received levels; we simulated avoidance by reducing marine
mammal densities exponentially over time;
3. a scenario that focused on humpback whales and assumed that humpback whale densities varied over the
winter season in Hawai'i. We only developed this scenario for humpback whales because they are the only
species for which the necessary data were available. Specifically, this scenario assumed that humpback
whale densities during the winter months would be described by a standard normal distribution with
densities increasing from zero starting in October, reaching a maximum between late-February through
March, then declining to zero again through the spring.
Every scenario assumed ship speeds of 10 knots (or 18.25 kilometers per hour), which is the same assumption
contained in the Navy’s and the Permits Division’s models. Both scenarios were based on estimates of the area the
would be ensonified at different received levels that the Navy presented in its Environmental Impact Statements for
the Hawai’i Range Complex (U.S. Navy 2007, 2008). Finally, every scenario was based on the Navy’s estimates of
the number of hours of the different kinds of active sonar that would be employed in the different exercises (future
Rim of the Pacific Exercises and other anti-submarine warfare exercises).
In addition, based on the results of a comprehensive program to establish the populations size and abundance of
humpback whales in the North Pacific Ocean, Calambokidis et al. (2008) provisionally estimated that about 10,000
humpback whales occupied waters off the Hawai’ian Islands during the winter months. This new estimate of
humpback whale abundance is almost twice the abundance estimate the U.S. Navy and the Permits Division used for
their models. To facilitate comparisons with the Navy’s and the Permits Division’s estimates, we calculated probable
exposures assuming humpback whale densities of 0.2186 (the same density the Navy and Permits Division used) and
densities of 0.4868 (to reflect the updated abundance estimates).
Further, by assuming that humpback whales have a constant density of 0.2186 for all winter months, the Navy’s
models effectively assume that all humpback whales arrive in Hawai'i on the same day, remain in Hawai'i until the
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