Page 39 - Summer 2015

Figure 1. General overlap between the auditory range of marine species and frequencies produced by man-made underwater sound sources. Human hearing range is provided as a reference. Note: hearing thresholds are not available for all species (e.g., baleen whales), so other data are used to predict hearing ranges (e.g., anatomy, vocalizations, and behavioral responses to sound). SURTASS, Surveillance Towed Array Sensor System.
incidentally as a by-product of operation, as in the case of sources associated with pile driving, drilling, or shipping.
The ability to accurately detect and interpret the relative im- portance of sounds in the surrounding environment as well as to communicate, navigate, and detect predators and prey is critical for many species living in the ocean where hear- ing is often their primary sensory modality (i.e., sound is capable of traveling over much greater distances compared with light in the marine environment). As a result of the di- versity of marine life in the ocean, there is a wide range of frequencies at which different animals use and hear sounds. Furthermore, there are numerous man-made sources in the marine environment with varying acoustical and physical characteristics. Many of these sources produce sound that overlap in space, time, and frequency (Figure 1) with those used by marine species. Thus there is a need to understand the impacts of man-made sounds on marine life and find and implement measures to avoid or mitigate impacts while still acknowledging the importance of the ocean to our economy and national security.
Concern over the impacts of man-made sound sources on marine species has been an issue for over 40 years (Payne and Webb, 1971). Some of the first activities to receive permits from NMFS in the 1990s were the acoustic thermometry of ocean climate (ATOC) program (Au et al., 1997) and the sci- entific research program associated with the US Navy Sur-
veillance Towed Array Sensor System Low Frequency Active (SURTASS LFA) program (Croll et al., 2001; Fristrup et al., 2003). Since that time, the mass stranding of beaked whale species associated with the use of tactical midfrequency on multiple occasions (Cox et al., 2006; Ketten, 2014) acted as “focusing events” for the public’s interest and awareness of the issue of underwater noise and protected species, in par- ticular marine mammals.
Under both the MMPA and ESA, activities that expose pro- tected species to certain sound levels may result in a “take” of the species and therefore require a permit or, in the case of a federal agency action, consultation with NMFS. “Take” is defined in the two statutes as to harass, hunt, capture, or kill or attempt to harass, hunt, capture, or kill any marine mammal under the MMPA and to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect or to at- tempt to engage in any such conduct under the ESA. Take is authorized under the MMPA if it is to have no more than a "negligible impact" (i.e., is not reasonably likely to adverse- ly affect the species or stock through effects on annual rates of recruitment or survival on those marine mammal species or stock) or under the ESA if it does not jeopardize the con- tinued existence of a species or destroy or adversely modify critical habitat (NMFS, 2014c,d).
The NMFS first established marine mammal acoustic thresh- olds in the late 1990s to help members of the public and
Summer 2015 | Acoustics Today | 37