The intense sound of seismic air guns used in oil exploration have disrupted the physiological response of narwhals. An article published on July 8 in the Journal of Functional Ecology provides a taste of the impact of seismic noise on the physiological responses of a deep-diving cetacean. Generally, this causes a strong increased energy cost of divingas the heart rate decreases.
According to Terrie Williams, a professor of ecology and evolutionary biology at the University of California Santa Cruz, the combination of minute heart rates and high-intensity exercise would be problematic for narwhals. That would affect the amount of blood and oxygen that can circulate.
The studies were carried out in Scoresby Sound, on the east coast of Greenland. Mads Peter Heide-Jørgensen, research professor at the Greenland Institute of Natural Resources, co-author of the study, has been analyzing the East Greenland narwhal population for more than a decade.
Noise exposure made narwhal heart rates unstable
In a previous study, Williams and her colleagues looked at narwhals released from nets set by native hunters. Physiological responses were similar, namely extremely low heart rates during intense exercise in a series of escape dives. According to Ms. Williams, the difference between the two events lies in the potential duration of the disturbance.
Exposure to noise made the heart rates of unstable narwhals. They could be extremely low due to fear, then very quickly become fast due to intense exercise. Reduced heart rate, or bradycardia, is said to be normal when mammal diving. However, during normal dives, the heart rate would still increase with exercise.
Deep-diving mammals generally save energy slipping during descents. However, during noise exposure, the narwhals escaped by swimming rather than sliding. Their heart rate was very low and their breathing at the surface was faster. This reaction would be particularly energy-intensive.
Devices have been created to better study these marine mammals
Over the past two decades, noise from human activities has reportedly caused mass strandings of cetaceans deep-diving, mostly beaked whales. That is why Williams’ group has developed instruments that allow researchers to monitor the exercise physiology of marine mammals during the dives.
The instruments were attached to the narwhals with suction cups and came off after one to three days. They then floated to the surface and the scientists could recover them. Williams and Heide-Jørgensen’s teams collaborated with native hunters in order to attach these monitoring devices.
SOURCE: MIRA NEWS