A spectacle of life
Each summer, the rocky shores of the Commander Islands transform into one of the Northern Hemisphere's most chaotic and densely packed wildlife spectacles. Around 20% of the world's northern fur seal (Callorhinus ursinus) population converges here to breed, with current estimates placing their numbers between 200,000 and 225,000 animals. The islands host four main rookeries: two on Bering Island and two on Medny Island, where the seals show strong fidelity, returning year after year to their birthplace.
The scene is dominated by extreme sexual dimorphism. Adult males, or bulls, can weigh up to 275 kg, while females rarely exceed 50 kg. The bulls arrive first in May, fasting for up to three months to aggressively defend small territories. Females arrive in mid-June, pregnant from the previous year. They give birth to a single pup within two days of arrival and then come into estrus just five or six days later, mating before their first feeding trip. The mothers then alternate between nursing their pup for one or two days on shore and foraging for fish and squid at sea for four to ten days, a cycle that lasts about four months. The movement, noise, and density of bodies create intense biological activity.
A history of discovery and destruction
The first naturalist to scientifically document this spectacle was Georg Wilhelm Steller in 1741. As part of Vitus Bering's Second Kamchatka Expedition, his ship, the St. Peter, was wrecked on what is now Bering Island. Stranded for nine months, Steller meticulously studied the island's fauna, including the fur seals, sea otters, and the now-extinct Steller's sea cow, before succumbing to scurvy and dying on the island. His detailed account, De Bestiis Marinis ("On the Beasts of the Sea"), described these animals for Western science.
Steller's discovery, however, initiated a period of intense exploitation. The Russian-American Company and other commercial hunters began harvesting the seals for their exceptionally dense fur. This unregulated pelagic (open-ocean) and land-based sealing took a massive toll. By the late 19th and early 20th centuries, the once-abundant populations across the North Pacific were on the verge of extirpation. The crisis prompted the North Pacific Fur Seal Convention of 1911, a landmark international treaty signed by the U.S., Russia, Japan, and Great Britain (for Canada) that banned hunting seals at sea. This, followed by stricter Soviet-era protections and the establishment of the Komandorsky Nature Reserve in 1993, allowed the Commander Islands' colonies to recover.