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Behavior

Is Noise Pollution Causing Marine Mammals to Starve?

This is a guest post by Celine Christiansen, an undergraduate contributor for Oceanbites. She is currently a candidate for a B.S in Biology, focusing on biomedicine, with a minor in English at Providence College. Her interests include Alzheimer’s disease, marine biology, human anatomy and physiology, and language. She enjoys writing and reading, traveling, and volunteering at the animal shelter. In the future, she hopes to either go to graduate school to complete a Physician Assistant program or attend medical school to continue helping others with her multicultural background and ability to speak multiple languages.

Article Source: Williams, T. M., T. L. Kendall, B. P. Richter, C. R. Ribeiro-French, J. S. John, K. L. Odell, B. A. Losch, D. A. Feuerbach, M. A. Stamper. 2017. Swimming and diving energetics in dolphins: a stroke-by-stroke analysis for predicting the cost of flight responses in wild odontocetes. Journal of Experimental Biology 220: 1135-1145; https://doi.org/10.1242/jeb.154245

Noise enters the ocean

The oil industry is harmful to marine birds and mammals with its massive spills that affect the ability of birds and other fur-bearing animals to stay dry. But the harm that the oil industry wreaks on marine life does not end with oil spills. Both the oil and gas industry uses massive air-gun explosions under the water, causing high-pressure waves that deafen the whales and dolphins beneath the surface. The noise is not limited to the oil and gas industry: the U.S. Navy uses sonar, which emits sound pulses to detect objects underwater every day as part of their monitoring and training exercises.

Sonar or radar distance measurement. (Wikipedia, Georg Wiora)

Noise pollution from multiple sources enters the ocean, from the sonar to the loud engines of ships. The noise travels from different directions and goes farther underwater than on land. But how exactly does this affect our marine life?

The study

Researchers from the University of California, Santa Cruz conducted demonstrations of the possible negative consequences of oceanic noise pollution on diving mammals. The scientists used six adult dolphins and one killer whale because they are diving mammals who must balance their speed and duration of breath-holding while they search.

The researchers trained the dolphins and the whale for six months with positive reinforcements. The mammals wore an ECG (electrocardiogram) recorder to measure their heart condition while they dived. The scientists also wanted to know how much oxygen each animal used, so they measured oxygen usage by having the animals breathe in a sealed, controlled environment. The study compared the animals’ dives and breathing patterns before and after sonar exposure.

Two dolphins swimming with killer whale. (THE CANADIAN PRESS/HO-Ocean Wise, National Oceanic and Atmospheric Administration)

What did they find?

They found that the whales swam differently when noise was introduced, from burst and glide to stroking, which is a riskier type of dive because it uses up more oxygen, decreasing the time underwater. For two of the dives, there was a nearly 20% decrease in dive time and a difference in swimming pattern (more stroking) after sonar exposure.

Whales require more energy to begin moving than dolphins. These energy costs, measured by the results of the ECG and their oxygen intake, can become really high a lot quicker when noise is introduced.

The dolphins showed similar results as they also used up more oxygen while they dived once exposed to sonar. Because they are smaller than a killer whale, they moved faster and used up more energy. Normally, during the dives, there isn’t much of a difference in their oxygen use when they are resting or swimming slowly; however, during faster swimming, their heart rate increased, and they used their stored oxygen quicker.

Burst and glide method of swimming. (The Mechanics and Physiology of Animal Swimming, Weihs)

The study found that the whales limited their dives and reduced their depth after sonar exposure. Whales also attempted to preserve as much oxygen as they could, as did the dolphins. The dolphins already increase their oxygen usage when swimming faster, which indicates that if the sound stresses the animals out and forces them to swim faster and more dangerously, they would use more oxygen.

This suggests that both species may have a hard time foraging successfully during the deep dives because they can’t stay underwater as long as they would without sonar. The study showed how exposure to sonar can change the mammal’s diving behavior from safe to more dangerous ones.

The bigger picture

All marine mammals are deeply affected by sonar disturbances in the water. This not only affects their ability to navigate through water, but it also affects how they find food, which can cause them to starve or even lose their families in the midst of their dangerous swimming methods. Multiple other studies have found the same result, which points toward the negative consequences of noise pollution on marine mammals.

While marine life may not see sonar, nor does sonar leave easily visible scars on ocean life, it presents a type of disturbance that may undermine the very survival of the iconic marine mammals that we know and love. The results from this study should serve as a warning for the potentially devastating long-term consequences of sonar in the oceans. The question is, how much more information is required for people to change the way the ocean and its life get treated?

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