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Last year, for the first time, scientists surveying Pacific Northwest salmon came up with empty nets. They weren’t all empty, but some were—and that’s “really different than anything we have ever seen,” David Huff of the NOAA survey team told The Seattle Times. It’s a bit too early to identify a particular cause of these unusual salmon surveys, but it’s not too early to be concerned.

Wild salmon populations are affected by dams, development, and salmon farms. Now, ocean and river temperatures are rising. That’s not good news for wild salmon.

At every life stage, salmon need clean, cold water. When water heats up, even by a few degrees, diseases can set in. Once it passes 73–77 degrees, salmon die.

That’s what happened in 2015, when unseasonably hot river water killed nearly half of the sockeye salmon that returned to the Columbia River to spawn in Oregon and Washington. And this year, fisheries managers estimate low returns because of a warming ocean and drought conditions for the third year in a row for California’s Sacramento River fall chinook—so low they’re recommending a significantly shortened commercial season.

Their sensitivity to changing environmental conditions make salmon susceptible to climate change, but it’s also why scientists use salmon as an indicator species to gauge the health of the ecosystem. We need salmon—and not just because they’re tasty.

1. Salmon feed forests.

On their journey out to sea and back, salmon feed humans, bears, orcas—and trees, too. It’s their unique life cycle that make them an important food source. Washington state biologists have estimated that salmon come into contact with 137 different species—and that’s not including plants. They’re such an important food source that scientists identify them as a “keystone species”—a species without which the ecosystem would change dramatically. Salmon spend most of their lives at sea. So when they return inland to spawn and die, they bring ocean nutrients—stored in their bodies—with them upstream, sometimes hundreds of miles, depositing nitrogen and phosphorus that forests need.

2. Salmon can tear down dams.

Almost four years ago, the largest dam removal project in U.S. history was completed, and scientists are already recording regeneration up and down the Elwha River in Washington state as it rushes back to life. The proposed removal of four dams on the Klamath River in 2020 would be even bigger in scale. And one driver behind dam removal is salmon. The federal relicensing process requires dams to make sometimes costly upgrades for fish passage under modern environmental laws. PacifiCorp, which owns and operates the four dams on the Klamath, has said in public statements that tearing the dams down is less costly than relicensing and maintaining them. When environmental laws protect salmon, removing dams makes economic sense.

3. Salmon sustain cultures.

Historically, members of the Karuk Tribe in Northern California ate more than one pound of salmon every day. Today, as dams, climate change, and development impact Klamath River salmon, that number averages less than five pounds of salmon eaten per person—in a year. In 2017, the tribe announced it would limit its harvest to just 200 chinook salmon. And it’s not just diet that’s impacted. All along the Pacific coast, Native people have lived alongside salmon for thousands of years. Salmon is at the center of ceremonies, art, and identity for tribes in the Pacific Northwest, Alaska, and California. When salmon are threatened, so is culture.

4. Salmon keep humans healthy.

Salmon is one of the most nutrient-dense foods for humans. It’s a healthy source of protein and has lots of vitamins and minerals, including vitamin B-12, magnesium, potassium, and selenium. And, of course, fatty fish like salmon have lots of omega-3s. We eat a lot of it. Worldwide, salmon overtook shrimp as the most traded seafood in 2016. And we pay a lot. Right now, a wild king salmon fillet is $37.99 from my local fish market in Seattle. That’s less for wild salmon than we used to pay because of competition from cheaper farmed salmon. But it may not be able to continue meeting the demand it helped create: Last year, sea lice—which kill Atlantic farmed salmon—caused a worldwide shortage.

5. Salmon shape the landscape.

When they spawn, salmon may move mountains, according to a recent study. Over millennia, salmon sex has helped to carve the mountain ranges of the Pacific Northwest. It works like this: When fish spawn, they stir up the river bed, digging holes for their eggs and swishing their tails in the process. That sends gravel downstream and also loosens the riverbed, making it less compact and more likely to move when the river floods. Over thousands of years, the tons of gravel that salmon move add up. The study, whose lead author is from Washington State University, showed that the landscape surrounding the streams where salmon spawn would be nearly a third taller if the salmon weren’t there.