Military Sonar Alters Whale Behavior

Some blue whales (Balaenoptera musculus) off the coast of California change their behavior when exposed to the sort of underwater sounds used during U.S. military exercises. The whales may alter diving behavior or temporarily avoid important feeding areas, according to new research by the Southern California Behavioral Response Study.

Researchers exposed tagged blue whales in the California Bight to simulated mid-frequency (3.5-4 kHz) sonar sounds significantly less intense than the military uses. "Whales clearly respond in some conditions by modifying diving behavior and temporarily avoiding areas where sounds were produced," said lead author Jeremy Goldbogen of Cascadia Research. "But overall the responses are complex and depend on a number of interacting factors," including whether the whales were feeding deep, shallow or not at all.

The scientists tagged the whales with non-invasive suction cups, which recorded acoustic data and high-resolution movements as the animals were exposed to the controlled sounds (Figure 1). 

whale

Figure 1. Examples of behavior changes of tagged blue whales during exposure experiments. The sound exposure periods are highlighted in blue on each track line. The location of the sound source is indicated by the large red circle. (From Goldbogen et al. 2013)

"The tag technology we use offers a unique glimpse into the underwater behavior of whales that otherwise would not be possible," said Ari Friedlaender, a research scientist at the Duke Marine Laboratory.

The scientists found that some of the whales engaged in deep feeding stopped eating and either sped up or moved away from the source of the noise. Not all of the whales responded to the noise, and not all in the same way.

"Blue whales are the largest animals that have ever lived. Populations globally remain at a fraction of their former numbers prior to whaling, and they appear regularly off the southern California coast, where they feed," said John Calambokidis, one of the projects lead investigators.

That area of the ocean is also the site of military training and testing exercises that involve loud mid-frequency sonar signals. Such sonar exercises have been associated with several unusual strandings of other marine mammal species (typically beaked whales) in the past. Until this study, almost no information was available about whether and how blue whales respond to sonar. 

"These are the first direct measurements of individual responses for any baleen whale species to these kinds of mid-frequency sonar signals," said Brandon Southall, chief scientist from SEA, Inc. "These findings help us understand risks to these animals from human sound and inform timely conservation and management decisions."

A related paper published by the same research team in
Biology Letters has shown clear and even stronger responses of Cuvier’s beaked whales (Ziphius cavirostris) to simulated mid-frequency sonar exposures. Beaked whales showed a variety of responses to both real, military sonar in the distance and nearby simulated sonar. What the beaked whales were doing at the time appeared to be a key factor affecting their reactions.

The research was funded by the U.S. Navy Chief of Naval Operations Environmental Readiness Division and the U.S. Office of Naval Research, and appears in the Proceedings of the Royal Society B. 

Source: Modified from materials provided by Duke University.

References
Goldbogen, JA et al. 2013. Blue whales respond to simulated mid-frequency military sonar. Proceedings of the Royal Academy B, DOI -10.1098/rspb.2013.0657

DeRuiter, S. et al. 2013. First direct measurements of behavioural responses by Cuvier's beaked whales to mid-frequency active sonar. Biology Letters, DOI – 10.1098/rsbl.2013.0223

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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.

whale1
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).

whale2
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).

whale3
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



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