Right Whales Stressed by Shipping Traffic

Tragic events often have unintended and far-reaching consequences. The destruction of the World Trade Towers by terrorists on September 11th 2001 was just such an event. It goes without saying that there were many consequences for humans, including two wars, increased airline screening, and shifts in the political landscape. But there were also consequences for other mammalian species as well.

Endangered North Atlantic right whales (
Eubalaena glacialis) gather during the late summer on calving grounds in the Bay of Fundy, Canada (Figure 1). A substantial portion of the calving grounds lies in an important shipping lane. Low frequency noise produced by ship engines and propellers travels long distances in water and is believed to interfere with acoustic signaling by whales. Previous studies have shown that right whales alter their vocalizations in response to increased underwater noise.

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Figure 1. A map of the Bay of Fundy, Canada showing the Right Whale Conservation Area and the shipping lanes. (From Rolland et al., 2012)

Rosalind Rolland from the New England Aquarium in Boston, and seven colleagues from across the United States, were collecting data on social behavior in right whales in the Bay of Fundy in August and September 2001. When shipping traffic ceased following the events of September 11
th, it presented the researchers with an unintended natural experiment. They realized that they had data that could test the hypothesis that shipping noise directly altered the behavior of North Atlantic right whales.

The researchers collected acoustic data, shipping traffic data, and fecal samples for right whales. The later were used to measure stress hormones (glucocorticoids) produced by the whales. Their results reveal a significant drop in low-frequency background noise in the days immediately following September 11
th when shipping traffic stopped in the Bay of Fundy (Figure 2).

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Figure 2. Power spectrum of underwater background noise from 2 days before and 2 days after 11 September 2001. There is a significant decline in low-frequency (< 150 Hz) noise after September 11 when shipping traffic stopped. (From Rolland et al., 2012)

Interestingly, the decline in background noise was correlated with decreased levels of stress hormones in right whales (Figure 3).

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Figure 3. (a) Fecal glucocorticoid levels in North Atlantic right whales before (grey boxes) and after (white boxes) 11 September for the years 2001–2005. (b) Significantly lower Fecal GC levels were significantly lower after 11 September only in 2001, when shipping traffic stopped for a few days resulting in a decrease in underwater low-frequency noise. (From Rolland et al., 2012)

This fortuitous study represents the first direct link between shipping traffic noise and stress levels in whales. It suggests that whales congregating in high traffic shipping lanes are chronically stressed by noise pollution.


References

Rolland, R., Parks, S., Hunt, K., Castellote, M., Corkeron, P., Nowacek, D., Wasser, S., & Kraus, S. (2012). Evidence that ship noise increases stress in right whales Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.2429