Sei Whales

The sei whale is one of the largest creatures on Earth. Adults can be more than 60 feet long and weigh as much as a fully loaded semi—the third-largest of all whales. And they’re found across the world, in all but the warmest and coldest waters. Yet they’re poorly known, by the public and scientists alike.

The sei whale—spelled S-E-I—gets its name from a Norwegian name for pollock, a cod-like fish. The name was bestowed because the fish and whales showed up at the same time of year.

Sei whales have rows of structures made from the same material as teeth and hair, known as baleen. The baleen filters plankton and tiny fish and squid from the water—about two tons per day.

Much about sei whales remains mysterious. In part, that’s because they live mainly in the deep ocean, away from shore. We know they’re usually alone or in small groups, and they can race at more than 30 miles an hour for short distances. But much of their life cycle is poorly understood.

Whalers killed a quarter of a million sei before the practice was banned. Recent population estimates range from perhaps 50,000 whales to as many as 80,000.

The whales face many threats. They can be hit by ships or entangled in fishing nets. And the warming climate can kill or displace their prey, forcing the whales to change their foraging and breeding grounds. Biologists are trying to find out more about this reclusive giant to better understand how it’s adapting to the environment.