Unicorns of the Sea Get Brain Freeze

ENVIRONMENT

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

A new study examines narwhals’ response to fear or stress. What is surprising about the findings? Read through the great Nat Geo article for some help.
- “Normally when an animal is scared, it either remains very still and slows its heart rate and metabolism in hope that danger will pass—like a possum playing dead, in an extreme case—or the body revs up to power a ‘fight or flight’ response.
- “But when narwhals get caught in fishing nets, surprisingly, they do both. Even as the narwhals pump their fins and tails as fast as they can to escape, their heart rates plummet to just three to four beats per minute.”

Why to scientists nickname this response “cardiac freeze” or “brain freeze”?
- The increased activity and decreased metabolism reduce the flow of blood to the narwhal’s heart and brain. “[A]nimals need to pump enough blood around the body to supply oxygen to the brain and stay warm … What’s more, the lack of blood flow could prevent the narwhals’ bodies from removing nitrogen, which leads to decompression sickness, also known as the bends.”
- The response is in no way related to ice cream headaches that humans experience! Those are called episodes of sphenopalatine ganglion neuralgia, and have to do with pain receptors in our mouths. Learn more here.

How did scientists conduct their test of narwhals’ reaction to stress?
- Scientists attached sophisticated devices directly to the animals using harmless suction cups. The devices included the following monitors:
  - electrocardiograph. This tool detects and records heart activity—the strength and pattern of heartbeats themselves, and the strength and timing of electrical impulses passing through each part of the narwhal’s heart.
  - depth recorder. As its name indicates, this part of the tool records how deep the narwhal dives in response to a threat.
  - acceleration recorder. This part of the tool records the velocity (speed and direction) of a narwhal’s dive.

That actually sounds like a pretty straightforward experiment. Why haven’t these studies been conducted before?
- According to Nat Geo, “[n]arwhals have always been a bit of a mystery.” In fact, these unicorns of the sea are so isolated that scientists can only estimate their population, and a narwhal has never been observed eating. (Students! That has someone’s dissertation written all over it!) Contributing to narwhals’ mystery:
  - remote habitat. Narwhals live entirely above the Arctic Circle, which is usually covered in thick sea ice.
  - behavior. Narwhals spend most of their time diving to depths of 1,372 meters (4,500 feet) or more.

What human activities may impact and increase narwhal stress?
- A variety of human activities, all linked to shrinking Arctic ice, may increase stress responses from narwhals. Learn more about shrinking Arctic ice cover here.
  - fishing. Although fishing is largely outlawed in the Arctic’s open ocean, small-scale whaling still takes place within Arctic nations’ exclusive economic zones. As the ice retreats, more ocean is available for fishing and whaling.
  - predation. Narwhals rely on slow, covert movements beneath a thick cover of sea ice for protection from killer whales, a major predator. Thinner sea ice will reduce the territory in which narwhals traditionally seek cover.
  - oceanic noise. Reduced sea ice will likely increase instances of shipping and seismic exploration. (Seismic exploration describes the use of shock waves to search for valuable commodities such as petroleum, natural gas, and minerals that may be embedded underground. Offshore drilling, conducted when seismic exploration is a success, is a huge economic industry in the Arctic. Learn more about the possible expansion of seismic exploration here.) Such underwater noise pollution may make narwhals more susceptible to stress-related “escape dives.”

TEACHERS TOOLKIT

National Geographic Education Blog