How Sharks Survive Frigid Water
Salmon Shark.
Credit: Scot Anderson

Salmon sharks spend much of their lives in ice-cold waters in the North Pacific. How do they stand it?

New research points to a special protein that may help them survive the frigid conditions.

Researchers attached satellite tags to 48 female salmon sharks in Prince William Sound, Alaska, to track their movements over three years. They also examined the sharks’ physiology to uncover how they endure winter waters dipping to 36 degrees Fahrenheit.

Salmon sharks maintain a 70-degree body temperature through high metabolic rates and internal heat exchanges. This study, by researchers at Stanford University, shows that salmon sharks also have an enhanced set of proteins that help their hearts contract at cold temperatures.

But even with these mechanisms in place, many of the sharks still bask in warmer surface waters during the winter, and others leave the region all together.

While most of the tagged salmon sharks spent their summers around North Pacific coast, half of them migrated south to California and the subtropics once cold winter temperatures set in. Some even went to Hawaii.

The researchers suggest that this previously unknown behavior is influenced by the two major driving forces of shark’s life: food and sex.

Prince William Sound is full of salmon and herring during the summer, but only herring in the winter, so these sharks may have left to look for food. Or they may be seeking warmer waters in which to give birth.

The findings will help ecologists improve ecosystem models for Prince William Sound. This type of satellite tracking, researchers say, could be used to create a map of shark habitats worldwide, a task that may prove critical to their protection.

This study is reported in the Oct. 7 issue of the journal Science.