VIDEO – In Alaska, the salmon run transforms the rivers into a gigantic feast for bears

Every summer, Alaska's rivers witness one of North America's greatest natural spectacles. After several years in the ocean, thousands of salmon return to the freshwater spawning grounds. This migration involves several species, including sockeye, pink, chum, coho, and king salmon. Guided by their sense of smell and by navigational mechanisms that are still being studied, the fish sometimes travel hundreds of kilometers upstream. Their progress is particularly impressive when they have to navigate rapids and waterfalls. The salmon leap out of the water to try to overcome these obstacles, often after several failed attempts.

Dozens of bears gather near the waterfalls.

This abundance attracts brown bears, who know the most favorable crossing points perfectly. In some areas, particularly around Brooks Falls in Katmai National Park, several dozen animals can be found near the same river. The bears position themselves in the water, on the banks, or directly at the foot of the falls. Some wait for salmon to almost leap into their mouths. Others catch them with their paws or dive completely to chase them. Not all bears have equal access to the best spots. The most powerful individuals generally occupy the areas where the fish are most numerous, while younger or less dominant bears must make do with less favorable areas.

A crucial period before winter

The salmon run is a crucial time for Alaskan bears. During this period, they can consume several fish a day and quickly build up the fat reserves essential for surviving the winter. Females must also prepare for pregnancy and nursing their cubs. The amount of food available during the summer can therefore directly influence their physical condition and their chances of reproduction. When salmon are particularly abundant, some bears become very selective. They primarily consume the most energy-rich parts, such as the skin, eggs, and brain, before discarding the rest of the carcass.

Salmon feed the entire forest

Migration doesn't only benefit bears. Carcasses left on riverbanks are consumed by foxes, wolves, birds, insects, and many other animals. After spawning, the majority of Pacific salmon die in the waterways. Their bodies decompose and release nutrients from the ocean, including nitrogen and phosphorus. These elements enrich the rivers, soils, and surrounding vegetation. Bears participate directly in this transfer by transporting the fish out of the water. Some of the marine nutrients thus end up in the forests along the rivers, where they contribute to the growth of plants and trees.

A particularly fragile natural balance

This spectacle, however, depends on the health of the salmon populations. Rising water temperatures, changes in river flow, the degradation of spawning grounds, and certain human activities can disrupt their migration. When salmon numbers decline, the consequences are felt throughout the entire ecosystem. Bears have less food, other predators scavenge fewer carcasses, and waterways receive fewer nutrients. For a few weeks, however, the annual run still transforms some Alaskan rivers into veritable hotbeds of life. Waterfalls become spectacular meeting points where fish and predators converge in a scene as brutal as it is essential to the balance of nature.