Andrea Odell, an undergraduate student in the University of Washington School of Aquatic and Fishery Sciences, tosses dead sockeye salmon onto the bank of Hansen Creek in southwest Alaska in August 2018 while other researchers record data and look for salmon in the stream. (Courtesy Photo | Dan DiNicola via University of Washington)

Andrea Odell, an undergraduate student in the University of Washington School of Aquatic and Fishery Sciences, tosses dead sockeye salmon onto the bank of Hansen Creek in southwest Alaska in August 2018 while other researchers record data and look for salmon in the stream. (Courtesy Photo | Dan DiNicola via University of Washington)

Researchers threw salmon carcasses on one side of a creek for 20 years. Here’s what happened.

How fast does a spruce tree grow? It depends on how many salmon die there, researchers show

With its network of tree-choked salmon streams, the Tongass National Forest has earned its moniker as the salmon forest.

It’s long been known that salmon fertilize forest growth. The fish contain marine nutrients like nitrogen. When salmon spawn and die in riparian areas, their carcasses feed the soil underneath, providing trees with nutrients otherwise unavailable.

Knowing that is one thing: it’s something most Alaskans grow up understanding. Measuring just how much salmon carcasses spur growth is another.

A long-running University of Washington salmon study in southwest Alaska has done just that. In a paper published Oct. 23 in the peer-reviewed journal “Ecology,” UW researcher Tom Quinn and colleagues have documented the growth of trees on one side of a river in southwest Alaska over the other.

The difference? Over 20 years of a fish count study, researchers flung sockeye salmon carcasses to only one side of Hansen Creek in the Bristol Bay region. It started out as an incidental decision — to avoid double counting fish, researchers decided to huck them onto the creek bank.

Quinn saw an opportunity for further research, electing to use only one side of the bank to gauge a possible effect.

“Tossing the carcasses to the left side started out just as a convenience to keep from counting the same fish twice. I thought at some point in the future, it would be kind of cool to see it if had an effect,” Quinn told UW media.

The paper, titled “A multi-decade experiment shows that fertilization by salmon carcasses enhanced tree growth in the riparian zone,” details how white spruce trees on one side of the creek grew faster than the non-fertilized side. Samples of 84 white spruce trees showed marine-derived nitrogen was incorporated into the new growth of trees on the enhanced bank.

The researchers threw 217,055 individual salmon, estimated to be over 600,000 pounds of fish, onto a 1.24-mile section of Hansen Creek over a 20 year period.

The effect was two-fold: trees on one side of the bank didn’t receive their customary dose of salmon feed, while trees on the other side received a second serving. The trees on the fertilized side weren’t noticeably taller, even though they grew faster. Trees on the salmon-enriched side started out shorter, which could explain the difference.

Quinn and his team took deep slices out of tree corps from white spruce on both sides of the stream. They examined growth of the tree rings during the 20-year period (1997-2016) as well as a 20-year period prior to the study (1977-1996), with growth measured in the earlier period serving as a control.

Both live sockeye salmon and fish carcasses are seen in Hansen Creek in 2014. (Courtesy Photo | Tom Quinn via University of Washington)

Both live sockeye salmon and fish carcasses are seen in Hansen Creek in 2014. (Courtesy Photo | Tom Quinn via University of Washington)

Kyla Bivens, an undergraduate student in the University of Washington School of Aquatic and Fishery Sciences, uses a hooked pole to throw a dead sockeye salmon onto the bank of Hansen Creek in southwest Alaska in August 2018. (Courtesy Photo | Dan DiNicola via University of Washington)

Kyla Bivens, an undergraduate student in the University of Washington School of Aquatic and Fishery Sciences, uses a hooked pole to throw a dead sockeye salmon onto the bank of Hansen Creek in southwest Alaska in August 2018. (Courtesy Photo | Dan DiNicola via University of Washington)

University of Washington researchers Martini Arostegui, left, and Jackie Carter tag sockeye salmon in 2015. (Courtesy Photo | Dennis Wise via University of Washington)

University of Washington researchers Martini Arostegui, left, and Jackie Carter tag sockeye salmon in 2015. (Courtesy Photo | Dennis Wise via University of Washington)

More in News

(Juneau Empire File)
Aurora forecast for the week of Nov. 27

These forecasts are courtesy of the University of Alaska Fairbanks’ Geophysical Institute… Continue reading

Rain at the National Weather Service Juneau station on Nov. 11 doesn’t exist as snow until hits the upper portion of nearby Thunder Mountain. So far this November has been both warmer and wetter than normal. (Photo by National Weather Service Juneau)
El Niño playing outsize role in Juneau’s warmer temperatures, according to National Weather Service

Early peek at numbers shows Juneau is 4.9 degrees warmer than average this November.

An emergency rescue vehicle parks in front of the Riverview Senior Living center at midday Monday after resident Nathan Bishop, 58, was discovered in the attic about 40 hours after he was reported missing. (Mark Sabbatini / Juneau Empire)
Nathan Bishop found alive in attic of Riverview Senior Living complex after 40-hour search

Family members say they remain supportive of facility’s locally available assisted living services.

Lisa Daugherty, owner of Juneau Composts!, stands in front of a recently acquired trommel screener, which separates different materials like soil, gravel, mulch and sand. She has invested $250,000 in the company since she started it in 2017. (Meredith Jordan/ Juneau Empire)
Federal dollars for public composting project concerns private-sector operator

Juneau Composts! owner says city project could ultimately shut down business

Charlene Apok leads Data for Indigenous Justice and works with the state’s Maternal Child Death Review to understand maternal mortality in Alaska. Apok analyzed data in their office on Sept. 25. (Photo by Claire Stremple/Alaska Beacon)
Data links Alaska’s sky-high maternal mortality rate to domestic violence

Studies show violence and overdoses cause more deaths than medical problems.

(Michael Penn / Juneau Empire File)
Police calls for Friday, Nov. 24, 2023

This report contains public information from law enforcement and public safety agencies.

(Michael Penn / Juneau Empire File)
Police calls for Thursday, Nov. 23, 2023

This report contains public information from law enforcement and public safety agencies.

(Michael Penn / Juneau Empire File)
Police calls for Wednesday, Nov. 22, 2023

This report contains public information from law enforcement and public safety agencies.

Nathan Bishop, 58, has been missing since Saturday evening, according to the Juneau Police Department. (Photo provided by the Juneau Police Department)
Search continuing for Juneau resident Nathan Bishop, 58, missing since Saturday evening

Police say Bishop “physically able, but suffers from Parkinson’s and dementia.”

Most Read