If I asked you to picture a brown bear, there’s a good chance you’d image one of Alaska’s massive bears standing in a stream, catching salmon. Can you see it now? More likely than not, you’re picturing Brooks Falls in Katmai National Park and Preserve. Don’t know it by name? Well, I’m sure you’ll recognize it by sight.

The sockeye salmon run

Each summer, sockeye salmon make their world-famous journey from the Pacific Ocean to the Nanek River Watershed and up the Brooks River, where many of them will be caught by one of dozens of brown bears standing in Brooks Falls. This annual congregation of bears is one of the planet’s more iconic naturally occurring events, but many fail to appreciate the most incredible part of this process; what happens right after our fishing friends have finished their meals. To get there, you first need to understand how remarkably cool sockeye salmon are.

The sockeye salmon is an anadromous species, meaning it’s born in freshwater, migrates to the ocean to mature into an adult, and returns to freshwater to spawn. During its journey to the ocean, sockeye often travel over 1000 miles (16,000 km), imprinting on the chemical signatures of the freshwater systems it passes through along the way. Once matured, nearly every individual fish will successfully follow the scent trail they’ve left for themselves and return to their natal stream. The salmon you’ve seen jumping through Brooks Falls are following these scents upstream through the Brooks River; where they were born about five years prior, and where they will die (after spawning).

Summertime meals for katmai’s bears

As brown bears awake in the spring after a season of hibernation, it’s time to put some weight on. Their diet is roughly 90% vegetarian, consisting of things like insects, broad-leaved herbs, tubers, sedges, berries, and roots. But, as June comes around and salmon return to the Brooks River, local bears get the opportunity to pack on those lbs. (more successful adults can catch and eat over 30 fish each day, which translates to something like 120 lbs. of meat). However, they’re not actually eating everything they catch. With that much food available, bears are able to get picky. They’ll only eat the fish’s fat rich-brains, skin, and eggs, leaving the carcasses behind.

As each bear catches its own salmon, many of the females and younger males will carry their fish away from the water to eat it. Remember: bears are somewhat solitary animals, and they aren’t concentrated by choice when they’re fishing, but by necessity (because the salmon are easiest to catch in small, specific areas of the river, like Brooks Falls). This can lead to hierarchical friction and competition over caught fish, so it makes more sense for the smaller bears to find a quieter spot to chow down rather than having their fish taken from them by a bigger, stronger bear.

The greater ecosystem

This is how bears, without realizing it, become a key contributor to the greater system’s nutrient availability. The left-behind salmon carcasses not only provide a low-energy-cost food source for animals like river otters, mink, and marten, but this marine-to-land nutrient transfer can have profound effects on the area’s forest. One study found that decomposing salmon in the region may contribute as much as 24% of the riparian soil’s nitrogen, which is critically important to riparian plant growth, size, and root strength. Another showed that Sitka spruce trees grew three times faster around streams where bear/salmon interactions were occurring annually, because the decomposition of salmon carcasses dumps nitrogen and phosphorus into the vegetation.

Not only do healthier plants provide better forage for moose, deer, and snowshoe hare, but they create a healthier stream system for a multitude of reasons (large and abundant trees capture sediment and slow erosion, woody debris provides external nutrients and aquatic habitat diversity, etc.). In this way, the salmon caught in Brooks Falls ultimately create a healthier habitat for future fish, which helps the salmon population itself thrive, which provides more fish for wildlife like bears to eat and leave to decompose. This naturally occurring positive feedback loop benefits the ecological system at each turn and will continue to do so as long as we keep its resources safe.

Although Brooks Falls marks the end of the road for many salmon on their thousand-mile journeys, it is this trip that stimulates and stabilizes an incredible landscape for Katmai’s awe-inspiring wildlife. Without the brown bears’ prowess and the sockeye’s ability to adapt and persevere, the landscape just wouldn’t be the same.  

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Samuel Bowlin is the Communications Director with WildLandscapes International, based in Boulder, Colorado. He can be reached at sbowlin@wildlandscapes.org.