The transition from wind-driven to mechanized shipping became the first step in what was to be a continued increase in the introduction of sound into the oceans. The oceans are much less transparent to light than to sound; as a result, many marine species use sound rather than light to navigate and communicate. Over the last 40 million years, marine mammals have evolved specializations for using underwater sound. The initial introduction of the propulsion sound of ships was unintentional, but engineers and scientists have also learned, with the development of sonar, how to use sound intentionally for underwater communication, navigation, and research. At some point as humans introduce more sound into the oceans, the conflict with evolutionarily-adapted marine mammal sound-sensing systems seems inevitable. Attention has been drawn to this issue through a series of marine mammal strandings, lawsuits, legislative hearings, and National Research Council (NRC) reports (1993, 2000, and 2003b) and, most recently, the draft report of the US Commission on Ocean Policy (2004).
Two earlier National Research Council reports (1994, 2000), while addressing biological issues of marine mammals and noise, also made recommendations that affected federal legislation and its implementation. The first was issued in 1994 in response to the feasibility test of a proposal to track global warming by monitoring the speed of an acoustic signal across an ocean basin (Munk et al., 1994). The feasibility test was to have set the stage for the full Acoustic Thermometry of the Ocean Climate (ATOC) experiment, but because of concerns over possible effects on marine mammals only a limited deployment of ATOC was attempted. The 1994 report recommended that there be legislative distinction between different types of “taking” and that the regulatory agencies streamline the permitting process for activities that did not kill or capture marine mammals. Additional streamlining was recommended for nonlethal activities that have negligible effects. The 2000 National Research Council report reviewed the marine mammal research program that was a component of the limited ATOC deployment. In Marine Mammals and Low-frequency Sound: Progress Since 1994, the committee noted that the 1994 amendments to the Marine Mammal Protection Act (MMPA) addressed some of the issues raised in the 1994 NRC report. The 1994 amendments introduced two levels of takes by harassment under the MMPA—level A and level B harassment. Level A harassment was defined in the 1994 amendments as “any act of pursuit, torment, or annoyance which has the potential to injure a marine mammal or marine mammal stock in the wild.” Level B harassment was defined as “any act of pursuit, torment, or annoyance which has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering.” However, the 2000 National Research Council report emphasized the importance of a criterion for significance of disruption of behavior (pg. 68):
- It does not make sense to regulate minor changes in behavior having no adverse impact; rather, regulations must focus on significant disruption of behaviors critical to survival and reproduction.
The report (pg. 69) recommended redefining level B harassment as any act that
- has the potential to disturb a marine mammal or marine mammal stock in the wild by causing meaningful disruption of biologically significant activities, including but not limited to, migration, breeding, care of young, predator avoidance or defense, and feeding.
Since the report was issued, the term biologically significant has been used in discussions of the 2003-2004 reauthorization of the MMPA (House Report 108-464). The US National Marine Fisheries Service (now National Oceanic and Atmospheric Administration [NOAA] Fisheries) has also used the term in decisions to grant incidental harassment authorizations. Scientific investigation and description of what would constitute “biologically significant” have not been pursued in a comprehensive manner.