Seismic surveys are a technique used to produce an image of rock formations beneath the earth’s surface
Seismic surveys are a technique used to produce an image of rock formations beneath the earth’s surface (http://en.wikipedia.org). For example, marine seismic surveys are used by Oil & Gas (O&G) companies to locate, and estimate size of oil and gas reserves under the seabed (www.seismicsurvey.com.au). Most marine seismic surveys operate using single or multiple towed arrays of seismic airguns, each airgun releases a bubble of compressed air directed down through the water column towards the seafloor. Sound waves are reflected by different layers of rock and received by hydrophone arrays, often arranged in ‘streamers’ towed behind the airguns. Signals are then processed to produce profiles of the substrate below the seabed. Explosive noise produced by seismic surveys can be loud, and low frequency; however, source level depends on the number and size of airguns in use. Although airguns are directed towards the seabed, it is possible that some noise readiates throughout the water column, and during certain circumstances may be heard many kilometres away (Thompson et al. 2013).
Marine mammals utilise sound for communication, navigation, foraging, and a multitude of social purposes. An increase in anthropogenic noise in the environment could interfere with their ability to perform these activities successfully and detect important biological sounds. In some cases, seismic surveys have been shown to affect the behaviour of marine mammals (Cato et al. 2013, Cerchio et al. 2014). Changes in behaviour ranged from rapid swimming away from the array, to changes in vocal behaviour. For more information on seismic surveys and the potential effects on marine mammals, please see: www.marinemammalseismic.co.uk and www.marinemammalseismic.com
Songs sung by male humpback whales (Megaptera novaeangliae) have long been associated with helping them attract a mate at, or en route to, their tropical breeding grounds. Song of each male within a population is very similar, with the same themes and order, and evolves constantly throughout the breeding season (Smith et al. 2008). Male humpback whales that remain on feeding grounds during the breeding season have also been detected singing songs; however, function of these songs is not understood, although they could play a role in an opportunistic mating strategy (Magnúsdóttir et al. 2014).
Anthropogenic noises in breeding areas can evoke avoidance behaviour in humpbacks, or parts of songs may be masked. Exclusion of animals could reduce number of potential mates for a singing male, and masking could mean remaining animals cannot hear the song, reducing the singer’s breeding potential further.
Cerchio et al. (2014) used Marine Autonomous Recording Units (MARUs) to record songs of male humpback whales off the coast of northern Angola, from March to December 2008. MARUs are static acoustic monitoring tools that can be used to record sounds created by marine mammals. Two MARUs were deployed offshore, near the edge of the Congo River Submarine Canyon, 9.65 km apart, with MARU 1 being further offshore than MARU 2. They were configured to record continuously for 80–100 days and deployed three times.
Whale songs were detected throughout the recording period with the first detection being on 9 June 2008. Detections increased during June and July, before remaining constant until November, where they began to decline. Pulses from a seismic survey were recorded in two periods, 4–30 July, and 14 October–1 December. Detections of pulses were relatively consistent for the duration of the first period, but more erratic during the second period.
Number of singing whales detected decreased significantly at both locations when received levels of seismic survey pulses increased. During both periods of pulse activity there appeared to be a greater reduction in the number of whales singing at MARU 2, and this is due possibly to higher received levels of seismic pulses at this location. The decrease in singing whales detected during seismic survey pulse periods shows that the whales have either ceased to sing, or moved to another location entirely. Cessation of singing was short term, with whales resuming singing after the seismic pulse period ended. The authors did note that it is possible that seismic pulses could have masked some songs, but unlikely due to the complex pattern of a song, and that reviewers were looking for patterns of multiple units of song, rather than single units.F
or more information on humpback whales and their songs or potential effects seismic surveys on humpbacks, see: Bombosch et al. (2014), Darling et al. (2014), Cato et al. (2013), Herman et al. (2013), Stanistreet et al. (2013), Van Opzeeland et al. (2013) and Weir (2008).
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|habitat modelling of humpback (Megaptera novaeangliae) and Antarctic minke (Balaenoptera bonaerensis) whales in the Southern Ocean as a planning tool for seismic surveys. Deep Sea Research Part I: Oceanographic Research Papers 91, 101-14.|
|Cato D.H., Michael J. Noad, Rebecca A. Dunlop, Robert D. McCauley, Kniest H., Paton D., Chandra P. Salgado Kent|
|& Jenner K.C.S. (2013) Behavioral responses of humpback whales to seismic air guns Journal of the Acoustical Society of America 133, 3495.|
|Cerchio S., Strindberg S., Collins T., Bennett C. & Rosenbaum H.C. (2014) Seismic surveys negatively affect humpback|
|whale singing activity off Northern Angola. PLoS ONE 9, e86464.|
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|whale songs recorded in the Philippines, Japan and Hawaii in 2006. Aquatic Biology 21, 93-107.|
|Herman L.M., Pack A.A., Spitz S.S., Herman E.Y.K., Rose K., Hakala S. & Deakos M.H. (2013) Humpback whale song:|
|who sings? Behavioral Ecology and Sociobiology, 1-11.|
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|Stanistreet J.E., Risch D. & Van Parijs S.M. (2013) Passive acoustic tracking of singing humpback whales|
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|Thompson P.M., Brookes K.L., Graham I.M., Barton T.R., Needham K., Bradbury G. & Merchant N.D. (2013)|
|Short-term disturbance by a commercial two-dimensional seismic survey does not lead to long-term displacement of harbour porpoises Proceedings of the Royal Society B: Biological Sciences 280, 1-8.|
|Van Opzeeland I., Van Parijs S., Kindermann L., Burkhardt E. & Boebel O. (2013) Calling in the cold:|
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|(Physeter macrocephalus), and Atlantic spotted dolphins (Stenella frontalis) to seismic exploration off Angola. Aquatic Mammals 34, 71-83.|