Narwhals react to loud seismic air guns used for oil exploration. This causes disruption in their normal physiological response to intense exercise. The result is an increase in the energy cost of diving, and paradoxically a reduction of heart rate. This alters oxygen and blood circulation.
“They’re swimming as hard and fast as they can to escape, and yet their heart beat is not increasing. We think this may be due to a fear reaction. The new study was led by Terrie Williams, a professor at UC Santa Cruz of ecology and evolutionary biology.
Published July 8, 2009 in the Journal of Functional EcologyThis study is the first to assess the effect of seismic noises on the physiological reactions of deep-diving cetaceans. Williams says that the combination of low heart rates, high heart rate variability, and intense exercise during deep diving poses a significant physiological challenge to narwhals. This is especially true if disruptions last as long as they would during extended oil exploration.
The high Arctic waters are where the sea ice has protected them from human disturbances for many millions of years. The region is now more accessible to shipping, exploration of natural resources, and other human activities due to the decline in polar seaice.
Williams and her coauthors have previously shown that narwhals entrapped in nets made by native hunters show a similar physiological response. This includes extremely low heart rate during intense exercise in a series escape dives. Williams explained that noise is more important than a capture event.
She said that while their heart rate returns to normal after they have escaped from the nets, it takes them three to four dives to get back to normal, but with the seismic ship moving through the water and the sound bouncing around, the escape reaction took place over a longer time.
Researchers also found extremely low heart rates in response to noise exposure. They also observed increased variability with heart rates changing rapidly between low heart rates that are associated with fear or high levels of intense exercise. Bradycardia is a normal part the mammalian dive response. However, during normal dives, the heart rate increases with exercise. Narwhals and deep-diving marine mammals like narwhals save energy by using gliders to descend to depth.
The noise exposure resulted in the narwhals performing 80% less diving descents during swimming, their heart rate dropping below 10 beats/minute, and their surface breathing being 1.5 times faster. Williams explained that the unusual reaction is extremely costly in terms energy consumption.
She said that the reaction was not only costly in terms of energy required to dive, but also takes away time for foraging for food.
The studies were conducted in Scoresby Sound on the east coast of Greenland, where coauthor Mads Peter Heide-Jørgensen, a research professor at the Greenland Institute of Natural Resources, has been studying the East Greenland narwhal population for more than a decade.
Williams’s team at UC Santa Cruz has developed instruments that allow scientists to monitor the exercise physiology marine mammals during diving. The suction cups were attached to narwhals and the instruments fell off within one to three days. They floated to the surface, where scientists could recover them.
Noise from human activities like military sonar has been linked over the past 20 years to mass strandings deep-diving cetaceans (mostly beaked whales). These deep-diving species are extremely difficult to study, and it was only through a partnership with indigenous hunters that Williams and Heide-Jørgensen’s teams were able to attach monitoring devices to narwhals.
Williams stated that most of the potential effects on animals occur underwater so it is difficult to study. “We are blessed to have the technology to show what is happening at depth for these animals in order to understand their biology.”
In addition to Williams and Heide-Jørgensen, the coauthors of the paper include Susan Blackwell at Greeneridge Sciences, Outi Tervo and Eva Garde at the Greenland Institute of Natural Resources, Mikkel-Holger Sinding at University of Copenhagen, and Beau Richter at UC Santa Cruz. This work was funded by the U.S. Office of Naval Research. Greenland Institute of Natural Resources. Greenland Agency for Mineral Resource Activities of Government of Greenland. The Carlsberg Foundation.