The Sound of Silence: Consequences of Man-made Noise on Humpback Whale Songs
This post belongs to a series written by students in the Conservation Biology course BSC4052 at the University of South Florida. This course provides an overview of major themes in conservation practice and related applied problems in biology, including: population ecology in the context of conservation, patterns of diversity, valuing diversity, threats to diversity, management actions and strategies for preserving diversity.
Article: Tsujii K, Akamatsu T, Okamoto R, Mori K, Mitani Y, Umeda N. 2018. Change in singing behavior of humpback whales caused by shipping noise. PLoS ONE 13:1-16. https://doi.org/10.1371/journal.pone.0204112
Author: Samantha Mitchell is a Marine Biology major at the University of South Florida. Growing up on Florida’s gulf coast has nurtured a love of marine life and a curiosity for the natural world. Passionate about science communication, she is looking forward to a career in science education and public outreach after graduation. Outside of school she volunteers with the Florida Fish and Wildlife Conservation Commission’s marine mammal pathobiology lab and local beach clean-ups as often as she can.
Male humpback whales sing loudly and for long durations during breeding season. A hundred years ago their voices did not have to compete with much man-made noise. These days they contend with underwater drilling, sonar, and the noise of thousands of cargo and passenger ships. This affects how and when they sing. The consequences of these changes are still largely unknown.
Humpback whales have several methods of communication. Both males and females slap the surface of the water using their fins, tails, or entire bodies and use short loud vocalizations (calls) to communicate. Only males use long repetitive calls that sometimes last for hours. These long-lasting vocalizations are referred to as songs and are primarily used during breeding season. The most basic components of songs are individual sounds that researchers call “units”. Several combined units create a phrase and combined phrases make up a theme. Themes are sung in succession in a continuous loop, composing a song (Mercado 2018).
This is a visualization of how whale song is composed. Each note is a unit. Repeats of the same unit are in the same color allowing us to visualize how each phrase is built and repeated to create the theme. Whale Song recording by David Rothenberg off the coast of Maui in 2010 and visualization by Mike Deal.
Humpback whale songs are passed on culturally across regions, change over time, and can travel more than 100 km (Mercado & Frazer 1998). While it is not known for certain, it is commonly believed that male whales use their songs to attract females to the breeding grounds, establish status, or announce their positions within the breeding grounds to other males. Clearly, singing is an integral part of humpback whale’s communication; so what happens when they must compete to be heard?
Adjusting the Volume
Increased shipping has substantially increased man-made noise in the marine environment, but quantifying noise generated by ships has been challenging. In modern shipping lanes, it is nearly impossible to regulate how much noise is being generated or to keep the noise level consistent across multiple days of study. In a recent study, Tsujii and colleagues (2018) tackled this problem by going somewhere where the sea is quiet. The Ogasawara Islands, 1000 km south of Tokyo are a quiet and remote patch of the Pacific where nearly 1,000 humpback whales gather during the breeding season. Here, Koki Tsujii and team placed two autonomous microphones 3 km apart and operated a passenger-cargo ship once a day. Since this was the only ship in the area, they could quantify how loud the ship was and regulate when and how long it operated for. The ship operated at up to 150 dB, as loud as a firecracker at short range (Paine 2019), a typical level for a ship that size and notably a similar range to that of a humpback whale song (151 – 173 dB).
Excuse Me, I am Talking!
Humpback whales in the area responded to the ship noise created in the study. Fewer whales sang in the immediate vicinity of the ship (500-1200 m) and those that did sing reduced the number of units in their songs. Furthermore, the silenced whales did not resume singing for a considerable time after the ship had passed: while it would only take 3 minutes for the levels of noise to return to normal, whales typically waited 30 minutes before singing again. These findings agree with other studies that show how shipping noise impacts the communication behaviors of marine mammals (Williams et al. 2015; Williams et al. 2019).
Yet while other researchers have seen modifications of frequency or volume, Tsuji’s team is the first to record whales truncating their established song or simply choosing to not sing at all. Do the missing units impact the efficacy of the song? Why do some whales stop singing? It is possible these are attempts to conserve energy rather than compete against the noise, but the answer is not clear.
Deal with It (or Don’t)
Humpback whales are a migratory species. The volume of their song allows them to communicate with other humpbacks far away, and the length of their song increases their chances of being heard by a passerby. If shipping noise can reduce or silence whale songs, how is it affecting how they communicate? What can be done to minimize acoustic disruption for baleen whales?
There has been limited research on the effect of man-made ocean noise on cetaceans, which means that most conservation management plans that are put in place are based on sparse data. Glacier Bay National Park in Alaska has put regulations in place on the number of ships entering the park, the speed they can travel at, and the pacing between ship arrival and departure times, with the intent to reduce boat strikes and mortality events. Only recently has the effectiveness of these efforts been monitored in terms of the acoustic impacts on the local humpback population (Frankel & Gabriele 2017). Other suggestions include: retrofitting noisy ships to be quieter, and moving large ships in and out of ports in convoys to decrease the duration of times spent at increased noise levels, or establishing “acoustic refuges” (areas where sources of man-made noise like drilling, sonar, and engines are restricted or prohibited) (Williams et al. 2019). Unfortunately, these are pricey, and may have substantial economic consequences. Yet with increasing human population and economic growth, the ocean is only going to become a noisier place (Williams et al. 2015), and we must understand how our growth and expansion affects cetacean communication or we risk doing further harm to these already vulnerable species.
Frankel A, Gabriele C. 2017. Predicting the acoustic exposure of humpback whales from cruise and tour vessel noise in Glacier Bay, Alaska, under different management strategies. Endangered Species Research 34:397-415.
Mercado E. 2018. The Sonar model for humpback whale song revised. Frontiers in Psychology 9.
Mercado E, Frazer LN. 1998. Environmental constraints on sound transmission by humpback whales. The Journal of the Acoustical Society of America 104:1827-1827.
Paine, G. 2019. Drones to deliver incessant buzzing noise, and packages. The Conversation.
Tsujii K, Akamatsu T, Okamoto R, Mori K, Mitani Y, Umeda N. 2018. Change in singing behavior of humpback whales caused by shipping noise. PLoS ONE 13:1-16.
Williams R, Veirs S, Veirs V, Ashe E, Mastick N. 2019. Approaches to reduce noise from ships operating in important killer whale habitats. Marine Pollution Bulletin 139:459-469.
Williams R., Wright, A. J., Ashe, E., Blight, L. K., Bruintjes, R.,Canessa, R. ,Clark, C. W., Cullis-Suzuki, S., Dakin, D. T., Erbe, C., Hammond, P. S., Merchant, N. D., O’Hara, P. D., Purser, J., Radford, A. N., Simpson, S. D., Thomas, L., Wale, M. A. 2015. Impacts of anthropogenic noise one marine life: Publication patterns, new discoveries and future directions in research and management. Ocean and Coastal Management 115: 17-24.