The Steller's sea eagle is named after Georg Steller, a German biologist who explored Kamchatka and Alaska in the 1700s. Its genus name, Haliaeetus, expresses that the principal diet of sea eagles is fish. It is the largest of the sea eagles and is called the heaviest known eagle, and it ranks with the harpy eagle and the Philippine eagle among the largest birds of prey.

Sources give its size in different ways. Animal Diversity Web gives the average mass as 6 kilograms for males and 9 kilograms for females. A 2009 paper from a Hokkaido wildlife center gives the wingspan as 210 cm (male) to 230 cm (female) and the mass as 5 to 7.5 kg. Another source says a female can weigh up to about 20 pounds (9 kilograms), and its wings can stretch up to 8 feet from tip to tip. Females are larger than males.

Scientists know little about Steller's sea eagles because their homes in the Russian Far East are remote. Kamchatka was a key Soviet military outpost and was off-limits to scientists until the mid-1980s. Conservation research on the eagles began in 1992 at Russia's Magadan State Nature Reserve, and in 2006 the San Diego Zoo and Natural Research Ltd. joined Russian scientists to study the movements of young eagles. Researchers use satellite tracking because the places where the eagles live are so remote.

To tag young eagles, scientists survey nests, and a team member climbs to a nestling and lowers it in a bag. A ground crew measures it, weighs it, takes tissue samples and fits a satellite leg tag. In 1997 and 1998 scientists fitted 29 nestlings with satellite transmitters, and 24 of them gave useful data about what they did after leaving the nest. Each transmitter weighed about 65 grams and was worn like a backpack on a Teflon ribbon, with a sewn link meant to wear away so the pack falls off.

The tags showed when and how far the young eagles moved. They left the area around the nest between 9 September and 6 December, and most left between 14 September and 21 October. Before migrating, they stopped at pre-migration sites on the lower parts of rivers, which may be places where many dead salmon are found after spawning. Most eagles from Magadan and the Amur migrated down the western edge of the Okhotsk Sea, while birds raised in Kamchatka moved down the Kuril Islands.

A study found that young eagles took 5 to 116 days to reach their first winter homes, and their migration averaged 51.3 kilometers a day. A published analysis of tracked young eagles found they averaged 47.8 km a day without stopovers, but only 22.9 km a day when stopovers were counted. Spring migration back north started between 2 February and 31 March. One tagged eagle was followed for 25 months, and its second autumn migration covered 1,839 kilometers at 20.9 to 22.4 kilometers a day.

In winter, many Steller's sea eagles fly south to Japan, but some stay in Kamchatka and move to open water. Hundreds gather at Kuril Lake in Kamchatka each winter to feed on salmon. The lake mostly stays free of ice because of springs, wind and its closeness to the sea. When fish became harder to find in winter, dead deer became a major food for the eagles wintering on Hokkaido, according to a 2009 paper. In spring 1995 satellite signals showed a tagged eagle had moved inland and stopped moving, and a colleague found it eating the remains of a deer.

The eagles eat mostly salmon. Besides fish, they eat crabs, shellfish, small animals, gulls and carrion, which is an animal already dead, and one will sometimes steal food from other birds. The big bill is described as hatchet-like and is suited to tough salmon skin. The eagle uses both eyes together, called binocular vision, to judge where its food is. It hunts from a perch or while flying and catches prey in its talons, and sometimes it stands in shallow water or on ice and grabs fish that swim by.

Scientists on Sakhalin and the Lower Amur collected most nest data from early July to late August, when nestlings are near fledging age and nest results are easiest to judge. A full clutch holds one or two eggs, rarely three, and a third nestling usually does not survive even if it hatches. A pair usually raises just one chick. Home range sizes are not known, but productive nests have been found as close as 100 meters apart. A pair often returns to the same nest each year and adds more branches to it.

As of November 2026, estimates put the world's Steller's sea eagles at around 5,000 birds, and several sources say the number is declining. The IUCN Red List lists the eagle as Vulnerable, and logging that harms their forest habitat is named as a threat. The eagles are protected by law in Russia, Japan, China and South Korea. No one knows for sure how long they live in the wild, and scientists know of no animal that preys on adult Steller's sea eagles.

A chick is covered in soft gray-white down that slowly changes to brown feathers, and a female lays one to three eggs in spring. A young eagle learns to fly when it is about 10 weeks old. Researcher Alexander Ladyguin found that Steller's sea eagle nestlings multiply their weight 40 times in less than two months on a diet of salmon.

Words to know

• genus: a group name
• transmitters: signal senders
• carrion: dead animal
• stopovers: rest stops
• fledging: leaving the nest