By shutting down the shivering response, a seal allows its body temperature to drop and achieves the benefits of hypothermia: a slower metabolism and lowered oxygen requirements which extends the dive time, Folkow said.
Taking the plunge
The seal experiment took place in a tank in which the seals took a series of experimental dives into cold water of 2-3° C. The researchers recorded shivering, heart rate, brain temperature and rectal temperature while the seals were on the surface and while they were diving.
The seals shivered on the surface but stopped or nearly stopped shivering when they dove, even though their bodies continued to cool. Their heart rates and temperatures dropped while they dove, but when they returned to the surface they restarted their shivering nearly immediately.
Seals have a remarkable capacity to store oxygen in their blood and muscles ?four times as much as humans ?to which they add this oxygen-conserving step of not shivering, Folkow said. By allowing body temperatures to drop, they slow metabolism and reduce oxygen demand. In addition, since shivering itself requires oxygen, there is an oxygen-conserving advantage to not shivering when diving.
In addition to slowing metabolism and generally reducing the need for oxygen, the researchers found that the seal's brain may cool about 3° C during the dives. The cooler brain requires less energy and oxygen and reduces the chance of damage caused by hypoxia, Folkow explained.
Achieved while remaining active
Seals have this physiological adaptation available just in case. This study found the seals can dive to more than 1,000 meters and for more than an hour. However, they usually take dives much shorter than their maximum capacity, and only occasionally perform very long dives. By limiting dive duration, seals maintain ae
Source:American Physiological Society