Whales and dolphins live in an increasingly noisy world; as our population increases and the demand for resources intensifies, so does the anthropogenic noise in our oceans. Cetaceans are exposed to sonar and other loud noises such as seismic surveys, gas exploration, and offshore development. Hearing is fundamental to cetaceans, who depend on it for communication, navigation, and foraging. Odontocetes, or toothed whales, use echolocation to navigate through their environment, to find food, and to communicate with others. Mysticetes, or baleen whales, also use vocalizations for communication; for example, humpback whales create low frequency “songs” during their breeding season to attract mates. Any loud noises that impact their hearing could be damaging, and in some cases, fatal. In fact, acoustic trauma has been the suspected cause of some mass stranding events. Military submarine exercises have been linked to several mass stranding events, such as the mass stranding of 17 cetaceans in the Bahamas in March 2000 following a US Navy sonar exercise, although actual evidence for harm is lacking. There is an urgent need to develop a method to investigate and quantify acoustic trauma in stranded whales and dolphins, in order to provide causation for stranding events and potentially link them to underwater noise.
Maria Morell and a team of scientists from the Scottish Marine Animal Stranding Scheme have developed a forensic technique to detect if stranded cetaceans have suffered from noise-induced hearing loss, using electron microscopy. They found that electron microscopy is able to detect structural alterations in the ears of long-finned pilot whales associated with mass stranding events in 2012 and 2015. They were able to detect lesions in the inner ear that can be associated with anthropogenic noise exposure in terrestrial animals. This method will be useful for quantifying hearing impairment and identifying the frequency range of noise overexposure responsible for hearing loss in cetaceans. This technique will give us a greater understanding of the impacts of underwater noise on cetaceans and may link some mass strandings to anthropogenic noise events. In turn, it will inform policy makers of the devastating effects of anthropogenic noise and influence ocean management decisions to help protect these magnificent creatures.
Morell, M. et al. Implementation of a method to visualize noise-induced hearing loss in mass stranded cetaceans. Sci. Rep. 7, 41848; doi: 10.1038/srep41848 (2017).
Filadelf, R. et al. Correlating military sonar use with beaked whale mass strandings: What do the historical data show? Aquatic Mammals; Moline 35.4 (2009): 435-444.
England, G.R., et al. Joint interim report Bahamas marine mammal stranding event of 15-16 March 2000. US Department of Commerce, US Secretary of the Navy (2001).