Abstract
Airguns used for offshore seismic exploration by the oil and gas industry contribute to globally increasing anthropogenic noise levels in the marine environment. There is concern that the omnidirectional, high intensity sound pulses created by airguns may alter fish physiology and behaviour. A controlled short-term field experiment was performed to investigate the effects of sound exposure from a seismic airgun on the physiology and behaviour of two socioeconomically and ecologically important marine fishes: the Atlantic cod (Gadus morhua) and saithe (Pollachius virens). Biologgers recording heart rate and body temperature and acoustic transmitters recording locomotory activity (i.e. acceleration) and depth were used to monitor free-swimming individuals during experimental sound exposures (18-60dB above ambient). Fish were held in a large sea cage (50m diameter; 25m depth) and exposed to sound exposure trials over a 3-day period. Concurrently, the behaviour of untagged cod and saithe was monitored using video recording. The cod exhibited reduced heart rate (bradycardia) in response to the particle motion component of the sound from the airgun, indicative of an initial flight response. No behavioural startle response to the airgun was observed; both cod and saithe changed both swimming depth and horizontal position more frequently during sound production. The saithe became more dispersed in response to the elevated sound levels. The fish seemed to habituate both physiologically and behaviourally with repeated exposure. In conclusion, the sound exposures induced over the time frames used in this study appear unlikely to be associated with long-term alterations in physiology or behaviour. However, additional research is needed to fully understand the ecological consequences of airgun use in marine ecosystems.
Highlights
Anthropogenic underwater sound generated by ships, power generation, oil and gas production, fishing, aquaculture and other industries is a growing concern as it may have negative impacts on fish and other marine organisms (Popper and Hastings, 2009; Boyed et al, 2011; Normandeau Associates Inc., 2012; Hawkins et al, 2015)
The weaker correlation between changes in heart rate and the particle motion (PM) component on day 2 may partly have been influenced by increased wave action, which lowered the quality of the PM measurement during the towed shooting that day
The decrease could have been to even lower levels, but 10 beats per minute was the lowest level that the heart rate data loggers were able to record
Summary
Anthropogenic underwater sound generated by ships, power generation, oil and gas production, fishing, aquaculture and other industries is a growing concern as it may have negative impacts on fish and other marine organisms (Popper and Hastings, 2009; Boyed et al, 2011; Normandeau Associates Inc., 2012; Hawkins et al, 2015). Depending on sound intensity and proximity, fish subjected to the noise from seismic airguns may incur physical damage (McCauley et al, 2003), physiological stress responses (Sierra-Flores et al, 2015) and/or exhibit behavioural changes (Løkkeborg and Soldal, 1993). The latter may include startle responses and flight (Wardle et al, 2001) and reactions like moving to unaffected areas (Løkkeborg and Soldal, 1993). In the case of repeated exposures, assessing cumulative effects is needed to determine relationships between dose and response and to design mitigation measures
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