In this section, I will run through some of the Acoustic concerns addressed in the Navy EIS. For an introduction and explanation of what the Navy EIS is, please read the into. The Navy EIS talks about several different types of effects from sound: Temporary Threshold Shift (TTS), Permanent Threshold Shift (PTS), Auditory Masking, Physiological Stress, and, Behavioral Reactions. Here are some simple definitions:
TTS: Temporary Deafness/Hearing Loss
PTS: Permanent Hearing Loss
Auditory Masking: When an animal can't hear important sounds because it gets lost in the ambient noise. This video does a good job letting you see how noise can hide a sound.
Physiological stress: Constant exposure to noise can cause stress in whales, which increases their stress hormones. Just like for humans, constant stress is bad for whales.
Behavioral Reactions: Whales and dolphins can change their behavior as a result of noise. These behavior changes may be relatively minor (from changing swimming speed) to very bad (separation of moms and calves, beaching).
The numbers of animals exposed to these sounds seems to be one of the most controversial issues on the internet, so I'll get to that first. Here are the tables which lay out how many individuals of each species will be exposed to sounds which are predicted to cause behavioral, TTS, and PTS reactions, depending on which "Action Alternative" the Navy uses. As you look at this table, notice that the numbers tend to be larger for more common species and species that have greater overall populations. For example, the numbers for short beaked common dolphins are very high, and this is also a very common species in the Naval Range. Other species, like Orcas, have very low numbers and occur very infrequently in the range (although they ARE known to occur).
Also, notice that there are two sources of impact on Marine Mammals - training and testing. Both of these are added up to get the total number of animals that may be exposed to sound.
The other thing to notice is that there are three "Alternatives," each with different levels of impact on marine mammals. These alternatives may expose different numbers of marine mammals to sound, with the "No Action Alternative" having the least impact on marine mammals, and "Alternative 2" having the greatest impact.
Table 3.4-14: Annual Testing Exposures for Sonar and Other Acoustic Sources (You can look at Annual Training Exposures here at Table 3.4-13).
And then this is the summary of the impacts of each alternative. The summary references Level A and Level B harassment, as defined by the Marine Mammal Protection Act. According to the Marine Mammal Protection Act, harassment is defined as "any act of pursuit, torment, or annoyance," which (for Level A harassment) has the potential to injure a marine mammal or marine mammal stock in the wild or (for Level B harassment) "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 but which does not have the potential to injure a marine mammal or marine mammal stock in the wild." For hearing, Level A harassment would be "the acoustic exposure associated with onset-permanent threshold shift." In layman's terms, Level A is anything that results in permanent hearing loss (which does not necessarily mean complete deafness). Level B is everything else, from temporary hearing loss to behavioral disturbance. One thing that bothers me about Level B is that it doesn't seem to account for cumulative hearing damage over time - but maybe when I get to the methods for calculating these numbers I'll find an explanation for that.
No Action Alternative:
Training and Testing Activities Under Alternative 1:
Training and Testing Activities Under Alternative 2:
So what is the difference between these three alternatives, and why do they predict that different numbers of marine mammals may be exposed to sound? Details of the three alternatives are here, but basically each alternative has increasing amounts of testing and training, and may cover a larger area (thus impacting more animals).
Up next: How were these numbers calculated?
P.S. Sorry if this is a little dense! I don't feel like I can summarize over 350 pages of controversial text in one short and hilarious blog post! Look, a beaked whale!