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FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013 An illustrative example of how a combination of stressors interact was provided by Relyea (2001, 2003, 2005) who demonstrated that exposing several different amphibians to a combination of pesticides and chemical cues of natural predators, which induced stress, increased the mortality rates of the amphibians (see also Sih et al. 2004). For some species, exposing the amphibians to the combination of stressors produced mortality rates that were twice as high as the mortality rates associated with each individual stressor. This section considers the evidence available to determine if interactions associated with mid-frequency active sonar are likely to produce responses we have not considered already or if interactions are likely to increase the severity — and, therefore, the potential consequences — of the responses we have already considered. The activities the U.S. proposes to conduct in the Hawai'i Range Complex will continue to introduce a suite of potential stressors into the marine and coastal ecosystem of the main Hawai’ian Islands that include mid-frequency and high-frequency active sonar from surface vessels, torpedoes, and dipping sonar; shock waves and sound fields associated with underwater detonations, acoustic and visual cues from surface vessels as they move through the ocean’s surface, and sounds transferred into the water column from fixed-wing aircraft, helicopters, and through the hulls of hulks that are the targets of sinking exercises. Exposing endangered and threatened marine animals in the Hawai'i Range Complex to each of these individual stressors could pose additional potential risks as the exposures accumulate over time. Exposing endangered and threatened marine animals to this suite of stressors could pose additional potential risks as the stressors interact with one another or with other stressors that already occur in waters off the main Hawai’ian Islands. Although we recognize these potential interactions and that these interactions might have effects on endangered and threatened species that we have not considered thus far; however, the data available do not allow us to do more than acknowledge the possibility. Consider the potential stressor that has received the most attention thus far: midfrequency active sonar. The proposed exercises would add mid-frequency sound to ambient oceanic noise levels, which, in turn, could have cumulative impacts on the ocean environment, including listed species. During transmissions, mid-frequency sonar will add to regional noise levels. However, there are no reliable methods for assessing potential interactions between these sound sources. The U.S. Navy conducted computer simulations to assess the potential cumulative impacts of mid-frequency active sonar (Navy 2008). That assessment concluded that the “cumulative impacts” of mid-frequency sonar would be “extremely small” because the proposed RIMPAC exercise would occur for a relatively short period of time every other year, for relatively short periods of time in any given area; the system would not be stationary, and the information available suggests that the effects of any midfrequency exposure would stop when transmissions stop. A greater cumulative impact is likely to result from an interaction between the number of times endangered or threatened species might be exposed to active sonar and explosions in association with the activities considered in this <strong>Opinion</strong> and other activities the U.S. Navy and other agencies plan to conduct in waters off Hawai'i during the same time interval. Each year from December 2008 through December 2013, the U.S. Navy plans on conducting Undersea Warfare Exercises in the Hawai'i Range Complex. Each of those exercises are expected to last for about 72 to 96 hours and involve about 140 hours of mid-frequency active sonar, 100 dips of dipping sonar, and 130 sonobuoys. Blue, fin, humpback, sei, sperm whales, and Hawai'ian monk seals are likely to be exposed to mid- 236
FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013 frequency active sonar associated with those exercises as well as the active sonar associated with the activities considered in this <strong>Opinion</strong>. As a result, each year from December 2008 through December 2013, individual blue, fin, sei, sperm whales, Hawai'ian monk seals, and humpback whales (seasonally) are likely to be exposed to the activities associated with a Rim of the Pacific Exercise and two Undersea Warfare Exercises; low-frequency active sonar transmissions associated with three SURTASS LFA missions; about 180 anti-submarine warfare tracking exercises, 19 bombing exercises; 18 anti-surface warfare torpedo exercises; and about 250 anti-submarine warfare torpedo exercises in addition to a stress regime that include close approaches for research, exposure to whale watch vessels; exposure to fisheries and fishing gear; and other natural and anthropogenic stressors. Richardson et al. (1995) provided extensive information and arguments about the potential cumulative effects of man-made noise on marine mammals. Those effects included masking, physiological effects and stress, habituation, and sensitization. Those concerns were echoed by Clark and Fristrup (2001), Michel et al. (2001), NRDC (2001), and others. Although all of these responses have been measured in terrestrial animals reacting to airborne, man-made noises, those studies are counterbalanced by studies of other terrestrial mammals that did not exhibit these responses to similar acoustic stimuli. The evidence available does not allow us to reach any conclusions about potential cumulative effects of the activities considered in this <strong>Opinion</strong> and other activities that are occurring or are designed to occur in the Hawai'i Range Complex. We could point to the increasing abundance of humpback whales over the past 30 years and infer that the status of these whales has improved despite the combination of natural and anthropogenic stressors in those waters. As a result, the existing stress regime in waters off Hawai'i would not reduce the performance of the humpback whales that winter in waters off Hawai'i. That inference is certainly consistent with the evidence available and it might be appropriate to extend that inference to the other endangered and threatened species in waters off Hawai'i (for example, the Hawai'ian nesting aggregation of green sea turtles have increased in abundance over the past 30 years as well). Other inferences, however, that would undercut that inference are also consistent with the evidence. If humpback whales in waters off Hawai'i were an isolated and resident population, it would be appropriate to infer that the existing stress regime has not reduced their performance as a population. Because that is not the case and the humpback whales that winter in Hawai'i migrate there from foraging areas across the North Pacific Ocean (humpback whales have been reported to migrate to Hawai'i from foraging areas in Russian, the Bering Sea, Aleutian Islands, western Gulf of Alaska, southeast Alaska, and British Columbia; Calambokidis et al. 2008). One inference that is consistent with the data is that the increase in humpback whales reflects conditions in foraging areas that allow their numbers to increase despite conditions in Hawai'i (the corollary being that as those conditions change, the population’s performance would change). Another inference that is consistent with the evidence available is that humpback whales continue to migrate to Hawai'i during the winter because these are their traditional wintering areas or because conditions in alternative wintering areas are worse. The information available does not allow us to determine whether or to what degree there are any interactions between the U.S. Navy activities considered in this <strong>Opinion</strong>, other activities the U.S. Navy is conducting or plans to 237
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