KEY QUESTIONS
- What are the hearing effects (TTS/PTS) of sound exposure on marine mammals?
- What are the behavioural reactions of marine mammals to sound exposure?

SUMMARY
Marine Mammal Noise Exposure Criteria: Updated Scientific Recommendations for Residual Hearing Effects and Assessing the Severity of Marine Mammal Behavioural Responses to Human Noise
Over a decade after the first Southall et al (2007) publication of marine mammal noise exposure criteria, a science team was supported to update the material to reflect new research results and knowledge gained from studies performed over the past decade. The revised exposure criteria to predict the onset of auditory effects of marine mammals includes updated audiograms, weighting function, and sound level exposure criteria for temporary and permanent auditory threshold shifts. The marine mammal function hearing groups were expanded from 5 to 6 to include all marine mammal species and in-air criteria for pinnipeds. New auditory weighting functions are less flattened and closer to audiograms than the previous M-weightings from Southall et al. (2007). The behavioural criteria work summarized the knowledge on behavioural effects and provided guidance rather than defining specific criteria.
Objectives and methods
Methods for revising the hearing effects and recommendations:
- Identify marine mammal hearing groups using available data on hearing, auditory anatomy, and sound production.
- Estimate hearing parameters for each species grouping and estimate group audiograms.
- Derive group-specific auditory weighting and noise exposure functions using generic bandpass filter equations and group-specific hearing and TTS data.
- Calculate group-specific TTS onset using either exposure functions (SEL) or extrapolation methods from TTS-onset measurements (SPL).
- Calculate group-specific PTS onset (both SEL and SPL) using estimates of TTS growth rates.
Methods for generating behavioural guidance:
- Evaluation of behavioral response severity to discrete exposures.
- Assessment of response severity methods from captive studies.
- Assessment of response severity methods from field studies.
- Evaluation of behavioral response severity to sustained (chronic) exposures.
Importance
This study was intentionally linked to:
- AEP Audiogram, Seasonal Movement Measurements and Vocalisation – Individual Minke Whales in Icelandic Waters in an effort to measure the hearing sensitivity of a live minke whale with electrophysiological methods.
- Assessing the Hearing Capabilities of Mysticete Whales where anatomy and anatomy-based models were suggested as a strategy to better assess mysticete hearing.
Links to other research
A number of SML Programme projects were reviewed in the process of developing the updated noise exposure criteria and behavioural guidance:
- Acoustic masking in marine mammals: A review and research strategy
- Temporary threshold shift (TTS) in odontocetes in responses to multiple air gun impulses
- Airgun Effects On Arctic Seals: Auditory Detection, Masking And TTS In Pinnipeds to understand TTS associated with airgun pulses in pinnipeds
- TTS growth and recovery in harbor porpoises exposed to intermittent and continuous signals
- Modelling Mysticete (Baleen Whale) Hearing
Institutions/PIs
Southall Environmental Associates, Inc. (Brandon Southall)