ONE MINUTE AT A TIME: ADVANCING OUR ABILITY TO ESTIMATE EFFECTS OF HUMAN SOUND ON MARINE LIFE
Martin, Steven Bruce
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Mitigating the effects of sound from man-made sources is an important component of marine conservation of marine mammals, fish and crustaceans. Sound travels from its source, through the ocean, to the animals that perceive it. Natural sounds include wind, waves, rain, ice, mammals, fish, and crustaceans. Man-made sounds include non-impulsive sources such as vessels and oil rigs, and impulsive sources such as seismic airguns, pile driving, and sonars. To protect animals from these sounds, safe thresholds are defined based on animal’s hearing and the daily sound exposure level (SEL). Safe thresholds for impulsive sounds are about 1/10th those of non-impulsive. To mitigate the effects of sound on marine life we need to better quantify the properties of man-made sources and the differences between non-impulsive and impulsive. This thesis provides such information. It is shown that seismic arrays have more energy above 1 kHz than previously reported and therefore have greater effects on marine life. Sound levels from impact pile driving depend on strike energy, pile penetration and the angle between pile and seabed. These factors change the distance that must be monitored to protect marine life by a factor of ten. The daily SEL and the autocorrelation of the one-minute sound exposure are used to describe the acoustic environment. These metrics are used to identify environments with and without human sound sources and the difference between different types of soundscapes, especially coral reefs from all others. Safe thresholds for sound exposure are based on the daily impulsive and non-impulsive SEL. Impulsive sounds change to non-impulsive-like over ranges of kilometers, and at some transition point they should accumulate with the non-impulsive SEL. Using kurtosis as a measure of impulsiveness and a proposed threshold for no possible injury, a new categorization of man-made sounds as impulsive or non-impulsive is presented that depends on the source and functional hearing group but not on range. This work will inform the development of regulatory protocols to help mitigate the effects of man-made sound on marine life.