- Epithelial/hair cell damage in fish ears and other tissue damage.
- At what exposures are fish killed or injured by industry sound sources (e.g. pile driving, airguns, explosions), and do they recover if injured?
- Physical Impacts: fish (with air-filled cavities), fish eggs and larvae, invertebrates.
- Are fish and invertebrates affected by some aspects of sound (e.g. particle motion, resonance, etc.) that do not affect marine mammals?
Two separate Programme activities were supported in an effort to determine whether fish exposed to airguns are at risk for epithelial hair cell damage. First, a Fish Tissue Injury Workshop was held in Stavanger, Norway 19-20 June 2007. Second, based on the recommendations of the workshop, a modeling study was undertaken to predict auditory tissue damage in fish.
Two recent papers in the scientific literature reached very different conclusions about the extent of hair cell damage caused by airguns. To resolve this difference, the Programme commissioned this project using first principals of engineering to model how the hearing apparatus of fish responds to sound exposure.
The purpose of this study was to show that a mathematical model of the biomechanics of the peripheral auditory system in fishes could be used to predict the onset of auditory tissue damage in different species and sizes.
Results to date show that no metrics correlate with TTS and auditory tissue damage in fishes, but a lumped parameter dynamic model of the auditory system can predict auditory sensitivity and potentially the occurrence of physical damage to fish based on calculations of relative motion of the inner ear as a function of frequency. Differences in source characteristics, water depth, hearing sensitivity among species, and origin of fish (wild vs aquaculture) were identified as the main contributors to explain why results differed between two recent papers examining the impact of airgun exposure on fish.
Objectives and methods
- The primary hypothesis was that acoustic trauma results when the inner ear receives excessive stimulation, which can then be correlated with different types and degrees of damage.
- A secondary hypothesis tested was that acoustic trauma in the inner ear will correlate with one or more sound exposure metrics (i.e., peak sound pressure level, sound exposure level, rise time, kurtosis, etc.).
- A biomechanical mathematical model based on fish anatomy and morphology was revised to calculate the relative motion between the otolith and the sensory epithelium that surrounds it in the inner ear for defined sound exposures as reported in the literature for three previous studies.
- The model was applied to five fish species.
Results from models developed in this study showed that because the two published papers (see other research) aimed at addressing that issue included different test conditions or subjects, neither is a definitive source to use in risk assessments of fish responses to airgun operations.
BioAcoustics LLP and The Pennsylvania State University (Mardi Hastings)