The Ecology of Glacial Rivers: Chinook salmon runs–what tagging has revealed

Fishwheel at Curry. Photo by Susitna Salmon Center

Fishwheel at Curry. Photo by Susitna Salmon Center

The sixth in a series from the Susitna Salmon Center. This segment by Jeff Davis deviates from the ecology theme to tell about chinook salmon runs in the Susitna River drainage:  When the run starts, how many king salmon move up several of the main tributaries, and what the radio tagging studies showed that was news to fisheries biologists.

The Susitna River drainage, like most large glacial rivers in Alaska, supports five species of Pacific salmon. Recent radio-tagging studies conducted by the Alaska Department of Fish and Game have provided new information on the abundance and distribution of returning adult salmon within the Susitna River drainage.

Salmon are an anadromous fish species, which means that they spawn in freshwater but spend part of their life cycle in the ocean. Chinook or King salmon are the first adult salmon species to enter the Susitna River drainage in the spring. Chinook salmon from the Susitna River drainage spend one year as juveniles rearing in fresh water, and most spend 3 or 4 years in the ocean.

The Alaska Department of Fish and Game captured, tagged and tracked Chinook salmon in 2012, 2013, and 2014 in the Susitna River drainage. Chinook salmon were captured in fish wheels and gill nets in the Lower Susitna River near the Yentna River 33 miles upstream from Cook Inlet and at a Middle River location near Curry, which is 120 miles upstream from Cook Inlet and 20 river miles upstream from Talkeetna. A tag that emits a radio signal was inserted into the stomach of captured salmon and then tracked as they passed by receivers distributed along the river or carried in airplanes.

During this current study, Chinook salmon entered the Susitna River in early June with the peak of the run passing the Yentna River near the middle of June. This is about 2 weeks earlier than the run timing of Chinook salmon determined from studies in the 1980s, which entered the river closer to the end of June. Chinook salmon captured in the lower river were on average 27 inches long when measured from their eye to the fork of their caudal fin, or tail.

Chinook salmon showed up at the Fishwheel near Curry in late June and early July with the peak of the run passing between July 13 and August 4. Tagged Chinook salmon traveled from 3 to 5 miles/day or 0.1 to 0.2 miles/hour. Chinook salmon captured near Curry were on average 28 inches long.

Approximately 88,000 Chinook salmon entered the Susitna River in 2014, which is close to the abundance estimates from the 1980’s. Around 22 thousand Chinook salmon went up the Yentna River, which is a large glacial tributary in the Lower Susitna River drainage, and 66 thousand went up the Susitna River. About 16 percent of the Chinook salmon tagged in the Lower River traveled to spawning locations in the Talkeetna River, 17 percent to spawning locations in the Chulitna River, and 6 percent to spawning locations in the Middle Susitna River upstream from Talkeetna. Most of the Chinook salmon, 25 percent, spawned within the Deshka River. Chinook salmon tagged in the Lower River spawned between June 22nd and September 2nd.

Most of the Chinook salmon tagged at the Curry site (42 percent) traveled to spawning locations in Portage Creek. Around 26 percent spawned in the Indian River, and approximately 1 % or an estimated 100 Chinook salmon spawned upstream of Devils Canyon, mostly in Kosina Creek or the Oshetna River. Chinook salmon tagged in the Middle Susitna River spawned between June 24th and August 10th.

Prior to this study it was thought that Chinook salmon only spawned in clear-water tributaries to glacial rivers; however, 1.5 percent of the Chinook salmon tagged in the Lower River, and over 7 percent of the Chinook salmon tagged at Curry spawned within the mainstem Susitna River.

Some mainstem Chinook salmon spawning locations were located near the mouths of tributary streams; however, many were not, and female Chinook salmon likely sought out spawning locations where groundwater was flowing up through the streambed, which would keep the redds free of fine sediments.

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The Ecology of Alaska’s Glacial Rivers

Episode 6. Chinook salmon spawning in the Susitna River drainage

By Jeff Davis, aquatic ecologist at the Susitna Salmon Center

 

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