An Alaskan grizzly bear eats a salmon. Photo: Jonathan Armstrong / Oregon State University

By Ed Yong
21 August 2017

(The Atlantic) – In the summer of 2014, William Deacy and Jonathan Armstrong returned to Kodiak Island, Alaska—a place where the world’s biggest grizzly bears gather to gorge themselves. Every year, hordes of sockeye salmon swim up from the ocean and fill the island’s streams in a spawning frenzy. Every year, the bears are waiting for them. And every year, Deacy and Armstrong had gone to wait for the bears.

But in 2014, the bears were gone.

For years, Deacy and Armstrong, both ecologists from Oregon State University, had spent time at one particular stream on the island—three meters across, and only six inches deep. In July and August, its shallow waters turn red with around 60,000 sockeye salmon. “They’re bank to bank,” says Deacy. “You’d have a hard time walking through the stream without catching one.”

The bears certainly have no problem. They kill around 70 percent of the spawning fish, and they focus on the most energy-rich organs. They’ll bite the humps off the backs of the males, and they’ll tear females open to get at their nutritious eggs. The signs of this massacre are evident. The tall grass on the stream’s banks gets so thoroughly flattened by the lumbering bears that it resembles a putting green. Gulls, scavenging from the cadavers, are so bloated that they can barely fly—and are liable to careen into human heads. And bits of shredded, half-eaten salmon float downstream.

“It’s usually terrifying to walk up the streams because you get a sense of carnage just around the next corner,” Armstrong says.

But in 2014: nothing. The grass was tall. The gulls were svelte. And the salmon were mostly untouched. Foxes, eagles, and wolves took their fair share, but without the bears, these lesser predators made the tiniest of dents in the salmon population. Most of the fish died naturally. “There’d be piles of dead salmon, just molding,” says Armstrong. “The bacteria were eating them instead of the bears.” […]

Most examples of these “phenological shifts” involve asynchrony between two partners. The case of the Kodiak bears represents “an under-recognized phenomenon—that of increasing synchrony of [natural] events due to climate change,” says Nicole Rafferty, from the University of California, Riverside. “And the consequences of this shift in foraging behavior could be large with knock-on effects for the ecosystem as a whole.”

“Species that never lived together can now interact because we’re removing the barrier of time,” says Armstrong. “We’ll see these new combinations that we never thought about, and we’ll get strong responses that no one could have ever predicted.” [more]

How Climate Change Canceled the Grizzly Salmon Run

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