A new peer-reviewed study published on Friday in the Journal of Functional Ecology found that narwhals experience disruptions in their normal physiological response to intense exercise when they detect the loud noise from seismic air guns used in oil exploration.
The study, conducted by researchers at UC Santa Cruz, is the first of its kind to explain the impact of seismic air guns on these animals.
According to lead study author Terrie Williams, a professor of ecology and evolutionary biology at UC Santa Cruz, the blast from the gun can cause low heart rates and sudden changes to heart rate, and these can be exacerbated because of the long periods of time the air guns are often used for in the oil industry.
"They’re swimming as hard as they can to get away, and yet their heart rate is not increasing—we think because of a fear response," Williams said. "This affects how much blood and oxygen can circulate, and that’s going to be problematic," said Terrie Williams, who led the new study.
In addition to unusually low heart rates, the researchers found that the heart rate variability increased when the narwhals were exposed to the air gun noise, rapidly switching between low heart rates associated with fear and fast heart rates associated with exercise.
Energy efficiency
“Not only is the reaction costly in terms of the energy needed for diving, the escape time will also take away from time spent foraging for food and other normal behaviors.”
Terrie Williams, lead author, professor of ecology and evolutionary biology, UC Santa Cruz
The researchers also found that the narwhals were much less energy efficient when exposed to the noise; narwhals and other deep-sea mammals preserve energy while descending into the water by gliding through the water instead of actively swimming. However, the researchers found that when the narwhals were exposed to the air gun noise, they glided 80% less while diving. In addition, their heart rates decreased to less than 10 beats per minute, their swimming strokes increased to over 40 strokes per minute and their breathing on the surface of the water was 1.5 times faster, UC Santa Cruz noted.
Willams said that this is unusually inefficient in terms of energy:
“Not only is the reaction costly in terms of the energy needed for diving, the escape time will also take away from time spent foraging for food and other normal behaviors,” she said.