1. Impact Assessment Methodology
Marine Mammal
Impact Assessment Methodology
USCHC 26 March 2018
Office of Coast Survey
National Oceanic and Atmospheric Administration

2. Planning Information Identify survey project Tabulate sonar sources
area bounds
Depth
Survey season
lineal km of sounding line expected
Tabulate sonar sources
Frequency
beam pattern
source level
Identify marine mammal populations
Population area densities by season
Hearing ranges by species
Office of Coast Survey
National Oceanic and Atmospheric Administration

3. Impact Field Determination
Use sonar data (frequency, source level, beam pattern plus salinity and temperature) to develop sound field with target isopleths (160 dB typically) for Harassment-Level takes. (Note: neither permanent or temporary hearing threshold shifts (injury) impacts are expected.)
Determine sound field cross-section area (constrained by depth if that is the case).
Office of Coast Survey
National Oceanic and Atmospheric Administration

4. Compute Impact Numbers
Convert animal population area densities to volumetric densities.
Multiply cross-section area by survey track length to establish insonified volume.
Compute the number of marine mammals impacted.
Office of Coast Survey
National Oceanic and Atmospheric Administration

5. Institute Best Practices
Vessel Speed
Observer Training for Vessel/Survey crew
Approach Distances
Others as appropriate
Office of Coast Survey
National Oceanic and Atmospheric Administration