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How do sea otters live in cold water? Surplus energy keeps them warm / Eivor Kuchta

Sea otters are the smallest marine mammal. As cold-water dwellers, staying warm is a top priority, but their dense fur only goes so far. We have long known that high metabolism generates the heat they need to survive, but we didn’t know how they were producing the heat — until now.

Researchers recently discovered that sea otters’ muscles use enough energy through leak respiration, energy not used to perform tasks, that it accounts for their high metabolic rate. The finding explains how sea otters survive in cold water.

Physiologist Tray Wright in the College of Education conducted the research along with colleagues Melinda Sheffield-Moore, expert on human skeletal muscle metabolism, Randall Davis and Heidi Pearson, marine mammal ecology experts, and Michael Murray, veterinarian at the Monterey Bay Aquarium.

The research team collected skeletal muscle samples from both northern and southern sea otters of varying ages and body masses. They measured respiratory capacity, the rate at which the muscle can use oxygen, finding that the energy produced by muscle is good for more than just movement.

“You mostly think of muscle as doing work to move the body,” Wright said. “When muscles are active, the energy they use for movement also generates heat.”

Wright said that because muscle makes up a large portion of body mass, often 40-50 percent in mammals, it can warm the body up quickly when it is active.

Sea otters’ muscles use enough energy through leak respiration that it accounts for their high metabolic rate, which keeps them warm in cool water.

A form of muscle-generated heat we are more familiar with is shivering. Wright said this involuntary movement allows the body to activate muscle by contracting to generate heat, while leak respiration can do the same without the tremors.