Estimating the risk of temporary acoustic threshold shift, caused by hydroacoustic devices, in whales in the Southern Ocean

Abstract

There is a potential threat to marine mammals from acoustic signals emitted by hydroacoustic devices. The impact on the hearing of marine mammals depends on the technical parameters of the instruments and on the exposure of the animal to noise pulses, as well as on the properties of the biological system, that is to say, on the anatomy and the audiogram of the animal. Here, the blue whale, the sperm whale and the beaked whale are taken as examples in an investigation of the potential exposure to noise pulses from the hydroacoustic instruments Hydrosweep and Parasound. Diving depths of the whales and relative speeds of the animals with respect to the survey vessels are taken into account, as well as the area impacted by the equipment, in estimating the level of sound needed to produce "temporary threshold shift" in an animal. The results suggest that auditory damage is only likely if animals pass the transducer at close range and that the impact on marine mammals can be mitigated by implementing prior detection and shut down procedures.

Impacts of local human activities on the Antarctic environment

“…It has been suggested that high source-level hydroacoustic equipment poses some risk to cetacean hearing and could potentially lead to auditory damage. Equipment of the strength and frequency implicated elsewhere in the world is not used in the Antarctic, although lower intensities may generate avoidance behaviour (SCAR 2006a, Kremser et al 2005.…”

“…Equipment of the strength and frequency implicated elsewhere in the world is not used in the Antarctic, although lower intensities may generate avoidance behaviour (SCAR 2006a, Kremser et al . 2005).…”

Categorizing Active Marine Acoustic Sources Based on Their Potential to Affect Marine Animals

“…Except for certain delphinids, which sometimes approach a stationary or moving vessel or towed sound sources, marine species generally can and often do avoid coming close to sound sources (e.g., [70]). NMFS has previously chosen a static 25 m radius around a source to describe the area that marine animals are unlikely to enter (e.g., 85 FR 14903 [64]), meaning that the 160 dB re 1 µPa criterion could be applied at this distance from the source.…”

“…Whereas the first four factors (Sections 3.3.1-3.3.4) are based on a single metric (e.g., transmission frequency, beamwidth) or a blended metric that combines two parameters (e.g., radiated power), the degree of exposure criterion is a composite factor that depends on aspects of the source (source level and directivity, pulse characteristics), the vessel (speed), and the animal (position relative to the source, total duration of received sound above a defined threshold). Qualitatively, lower source levels, greater source directivity, faster vessel speeds, and an animal's greater distance from the source (e.g., [70]) are usually associated with a lower degree of exposure. Pulse rate and pulse length, which are not explicitly mentioned in these qualitative considerations, require deeper examination, as does the total duration of exposure.…”

“…There has also been little consideration given to the speed of moving sources relative to animals. Faster vessels clear an area more rapidly (e.g., [70,74]), leading to lower exposures in most cases, even while the risk of a vessel strike or entanglement in towed equipment could be greater for higher vessel speeds.…”