| Summary: | Seismic airguns are devices used to find oil and gas deposits under the seafloor. They produce a loud percussive sound every 10 to 20 seconds usually for extended periods, and there is concern that these sounds may have a negative impact on nearby marine mammals. Determining the impacts of various industrial activities in the marine environment can be very difficult, particularly behavioural effects on marine mammals. Marine mammals are mobile and cryptic, being difficult to follow and behaviourally assess, particularly when not at the surface. In the first year of a four year study we conducted a behavioural response study (‘BRS’) exposing humpback whales to the sounds of a small (20 cubic inch volume) airgun as they moved through our study site north of Brisbane. The aim was to record the behavioural responses and determine which factors involved in the interaction are most strongly correlated with the degree of change (e.g. received level, proximity of the airgun, social behaviour of the whale group) and whether or not these behavioural changes are likely to have longer term biological effects. The whales were followed from three different platforms: elevated land stations, small boats and high resolution behavioural tags attached to the whales (Dtags). During each trial one to three groups of whales were followed and behavioural observations recorded for at least 1h preexposure, then 1h during ‘exposure’, and 1h post-exposure. ‘Exposure’ included one of four treatments: two different tow paths (east and north) each with either the airgun firing (‘active’) or the airgun towed behind the source vessel but not firing (‘control’). Acoustic loggers and hydrophone buoys were also deployed to measure the acoustic environment including the acoustic level of the airgun and the acoustic behaviour of the whales. Overt behavioural responses included whales moving rapidly towards the source vessel while avoidance reactions were more subtle than expected. Future experiments at this site and offshore north of Exmouth Gulf will include experiments with larger arrays of airguns including one typical for industry.
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