The ocean is a noisy place, as, unlike light and other possible stimuli, sound can travel very efficiently in seawater. Anthropogenic noise pollution in the marine environment is becoming a large concern – underwater noise created by ships and other human-related sources can be detected many kilometres away, far beyond what would be seen or heard on land. Seismic surveys produce some of the most intense noises in the ocean, and can often operate for an extended period of time. Many cetaceans rely on sound to forage, find mates, avoid predators, navigate and communicate. One can imagine the possible harmful effects of powerful seismic survey sounds on acoustically sensitive marine mammals like whales and dolphins. Effects can be divided into 4 categories: physical and physiological effects, perceptual effects, behavioural effects, and indirect effects. Physical and physiological effects include damage to body tissues, permanent reduction in auditory sensitivity, reduction in auditory sensitivity with eventual recovery, and chronic stress. Perceptual effects include masking biologically significant sounds (such as those used in echolocation, and communication among others). Behavioural effects include the disruption of foraging, area avoidance, changes in diving and respiration patterns, and changes in vocalisation. Indirect effects include reduced prey availability (fish are affected too) which results in reduced feeding rates. Unfortunately a large amount of uncertainty exists around the possible effects of noise on cetaceans, and other marine mammals. Some studies have even shown no effects of seismic surveys on whales and dolphins present in the area, but these are in the minority. However, the difficulties of studying cetaceans which spend all of their lives at sea, and most of it submerged, are well-known. In any case, despite the uncertainties that exist regarding the effects of seismic survey noise on cetaceans, the development and implementation of a precautionary approach to seismic surveys is needed to safeguard individuals and the population. In addition to noise, other threats from seismic surveys come in the form of entanglement in airgun array gear.
This is the second in a series of blogs which will look into seismic surveys in a marine environment.
Written by: Minke Witteveen
For further reading:
- Jasny, M. 2010. Boom, Baby, Boom: The Environmental Impacts of Seismic Surveys. Accessed: 2017-01-14. URL: https://www.nrdc.org/resources/boom-baby-boom-environmental-impacts-seismic-surveys
- Gordon, J.C.D., Gillespie, D., Potter, J., Frantzis, A., Simmonds, M.P., Swift, R. and Thompson, D. A review of the effects of seismic survey on marine mammals. Marine Technology Society Journal 37: 14-32.