Saving City Salmon
INTRO: As Alaska's cities get bigger, streams that once supported healthy runs of salmon now find themselves polluted, re-routed or otherwise altered. Chester Creek is one such stream. It flows through the center of Anchorage, Alaska's largest city. As Doug Schneider reports in this week's Arctic Science Journeys Radio, a scientist who studied the creek offers suggestions to save the creek's city salmon.
STORY: Photographs taken in the early 1900s show early day settlers harvesting salmon along Chester Creek, when it was still just a place in the vast Alaska wilderness. Today, Chester Creek is an urban salmon stream, set mid the hustle and bustle of Anchorage's 250,000 people. The creek begins high in the still undeveloped Chugach Mountains north of the city, but then quickly finds itself winding through the many neighborhoods, busy streets, and business parks of the city's midtown section.
Ultimately, the stream empties into Westchester Lagoon, an artificial lake created by a small dam and culvert system near the mouth of the creek. Culverts allow the water to flow from the lagoon into the nearby ocean.
A lot has changed since the first settlers came to Alaska. What was once a vibrant salmon stream now hosts only a small run of wild coho salmon. In a state famous for salmon, urbanization is taking a toll on the state's inner-city salmon streams. Matthew Whitman is a graduate student at the University of Alaska Fairbanks who studied the impacts of urbanization on Chester Creek and its salmon.
WHITMAN: "Well, it's in the northern region of Anchorage. If you're familiar with Anchorage, it's one of the older and more developed parts of the city. Historically there was a large coho salmon run in that stream. Since the 1950s there has been major development in that part of the city and today there is only a remnant population of salmon that return to the stream."
To learn why salmon aren't doing well in Chester Creek, Whitman first had to understand the characteristics of a healthy salmon stream. He reviewed hundreds of studies on salmon streams across the country and came up with a kind of checklist.
To start, good salmon streams should offer a diversity of habitats-places with woody debris for small fish to hide, for example. Steams should have stretches of riffles, along with stretches of pools; some deep, and some shallow. Salmon also need unfettered access to good spawning areas. Log jams, bridges, dams, and other impediments are the kiss of death to salmon. The water temperature needs to be just right, and there needs to be plenty of dissolved oxygen and nutrients like phosphorous and nitrogen.
WHITMAN: "What else do they need? Well, there are other important things to look at in the streambed itself. Are there gravels and cobbles and are they suitable size for spawning? Are there too many fines of a certain size that would choke of the nests so that there isn't good water flow into the reds during the incubation phase?"
According to Whitman, Chester Creek falls short in several of these key requirements. Habitat diversity is lacking. Where once trees and brush shaded the waterway, paved roads now cross its path, while parking lots and manicured lawns stretch to its banks in many places. The creek also is too shallow in spots, and at times the water is too hot and has too little oxygen. Whitman says culverts bring runoff along with pollutants and sediment into the creek. The runoff can be intense at times, and can wash away salmon eggs and destroy habitat. But most troublesome are the human barriers—bridges, culverts, and dams—that impede salmon migration. Whitman says the most important barrier is the dam and culvert system at the mouth of the creek itself.
WHITMAN: "There is a problematic barrier at the mouth of the creek. Adults can make it through but it's widespread knowledge that it is very inefficient and difficult."
To be sure, Chester Creek isn't the only salmon stream running through Anchorage. Nearby, Campbell Creek and Ship Creek continue to support salmon, and studies of their health also are underway. And just outside town, in an area that is under increasing development pressure, is Rabbit Creek. Presently the stream hosts a healthy run of wild salmon. But Whitman says that could change.
WHITMAN: "Rabbit Creek is in an area that is being developed, so it might be important to learn some things from Chester Creek and apply them to Rabbit Creek so we don't see the same sort of things happen to coho salmon in that stream."
Whitman says community groups are organizing efforts to rehabilitate Chester Creek. He hopes his study will help them decide what problems to tackle first. Anchorage isn't the only large Alaska city with urban salmon streams, either. The Chena River, which runs through the center of Fairbanks, also has come under increased development pressure and declining salmon returns.
This is Arctic Science Journeys Radio, a production of Alaska Sea Grant. I'm Doug Schneider.
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Thanks to the following individuals for help preparing this script:
Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks.
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