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

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FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013 frequency range of their songs. Fernandez-Juricic et al. (2005) reported that house finches (Carpodacus mexicanus) adopted the same strategy to compensate for background noise. Although this form of vocal adjustment has not been studied extensively in marine animals, Dahlheim (1987) studied the effects of man-made noise, including ship, outboard engine and oil-drilling sounds, on gray whale calling and surface behaviours in the San Ignacio Lagoon, Baja, California. She reported statistically significant increases in the calling rates of gray whales and changes in calling structure (as well as swimming direction and surface behaviours) after exposure to increased noise levels during playback experiments. Although whale responses varied with the type and presentation of the noise source, she reported that gray whales generally increased their calling rates, the level of calls received, the number of frequency-modulated calls, number of pulses produced per pulsed-call series and call repetition rate as noise levels increased. Parks et al. (2007) reported that surface active groups of North Atlantic right whales would adopt this strategy as the level of ambient noise increased. As ambient noise levels increased from low to high, the minimum frequency of right whale “scream calls” increased from 381.4 Hz (± 16.50), at low levels of ambient noise, to 390.3 Hz (± 15.14) at medium noise levels, to 422.4 Hz (± 15.55) at high noise levels. Surface active groups of North Atlantic right whales would also increase the duration and the inter-call interval of their vocalizations as the level of ambient noise increased. As noise levels increased from low to high, the duration of right whale “scream calls” would increase from 1.18 seconds (± 0.08) at low levels of ambient noise to 1.22 seconds (± 0.08) at high noise levels (durations decreased to 1.11 seconds ± 0.07 at medium noise levels). The inter-call intervals of these vocalizations would increase from 17.9 seconds (± 5.06) at low levels of ambient noise, to 18.5 seconds (± 4.55) at medium noise levels, to 28.1 seconds (± 4.63) at high noise levels. Biassoni et al. (2001) studied the effects of exposing sining humpback whales to low-frequency active sonar in Hawai'i. They concluded that the average number of phrases did not differ with exposure; longer songs during exposure had more phrase repetitions and were, as a result, more redundant. Singers also switched from a frequency modulated to a rarer amplitude modulated phrase type overlapping sonar transmissions. Finding rapid and dynamic changes in humpback whale displays in response to LFA sonar suggests that singers have an ability to compensate for interference to anthropogenic sounds. POTENTIAL FITNESS CONSEQUENCES OF VOCAL ADJUSTMENTS. Although the fitness consequences of these vocal adjustments remain unknown, like most other trade-offs animals must make, some of these strategies probably come at a cost (Patricelli et al. 2006). For example, vocalizing more loudly in noisy environments may have energetic costs that decrease the net benefits of vocal adjustment and alter the bird’s energy budget (Brumm 2004, Wood and Yezerinac 2006). Lambrechts (1996) argued that shifting songs and calls to higher frequencies was also likely to incur energetic costs. In addition, Patricelli et al. (2006) argued that females of many species use the songs and calls of males to determine whether a male is an appropriate potential mate (that is, the must recognize the singer as a member of their species); if males must adjust the frequency or temporal features of their vocalizations to avoid masking by noise, they may no longer be recognized by females of the same species (Brumm 2004, Slabbekoorn and Peet 2003, Wood and Yezerinac 2006). Although this line of reasoning was developed for bird species, the same line of reasoning should 204
FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013 apply to marine mammals, particularly for species like fin and sei whales whose song structures appear to be very similar. However, if an animal fails to make vocal adjustments in presence of masking noise, that failure might cause the animal to experience reduced reproductive success or longevity because it fails to communicate effectively with other members of its species or social group, including potential mates. Based on the evidence available, the endangered baleen whales that are considered in this <strong>Opinion</strong> — blue, fin, and sei whales — are not likely to experience impaired communication because they vocalize at frequencies that are much lower than mid-frequency active sonar. Because Hawai’ian monk seals and the endangered and threatened sea turtles that are considered in this <strong>Opinion</strong> do not appear to vocalize, they are not likely to experience impaired communication by mid-frequency active sonar. Field investigations of humpback whale songs suggest that humpback whales have an upper frequency limit reaching as high as 24 kHz (Au et al. 2006). Based on this information, it is reasonable to assume that the active midfrequency sonar the U.S. Navy would employ during the proposed Rim-of-the-Pacific Exercises and RDT&E activities is within the vocalization range of humpback whales. As a result, we assume that some of the humpback whales that are exposed to mid-frequency active sonar during one or more of the proposed exercises might experience impaired communication as a result of that exposure. Because the dominant energy in humpback whale songs and calls are in frequency ranges that are substantially lower than that of mid-frequency active sonar, however, we believe humpback whales are likely to protect the saliency of their songs and calls without making the vocal adjustments that have been reported for North Atlantic right whales confronted with increases in continuous, lowfrequency sound sources. The evidence available leads us to the opposite conclusion for sperm whales: based on their hearing sensitivities, which overlap the frequency range of mid-frequency active sonar, sonar transmissions might temporarily reduce the active space of some sperm whale vocalizations. Most of the energy of sperm whales clicks is concentrated at 2 to 4 kHz and 10 to 16 kHz, which overlaps with the mid-frequency sonar. Other studies indicate sperm whales’ wideband clicks contain energy between 0.1 and 20 kHz (Weilgart and Whitehead 1993, Goold and Jones 1995). Ridgway and Carder (2001) measured low-frequency, high amplitude clicks with peak frequencies at 500 Hz to 3 kHz from a neonate sperm whale. As a result, we assume that some of the sperm whales that are exposed to mid-frequency active sonar during one or more of the proposed exercises might experience impaired communication as a result of that exposure. Because the dominant energy in sperm whale songs and calls overlaps with the frequency range of mid-frequency active sonar, sperm whales may have to make one or more of the vocal adjustments discussed in this subsection to preserve the saliency of their vocalizations. Because any reductions in the active space of sperm whales caused by active sonar transmissions associated with the proposed exercises would be temporary and episodic, any these vocal adjustments sperm whales would have to make would also be temporary. 205
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