Nutrient Supplementation Study
The Nutrient Supplementation Study (or Nutrification Study) began in the year 2000 and ended as scheduled in 2012.
The goal of the project has been to determine the appropriate number of adult salmon which should allowed to return to the Dewatto River to meet the capacity of the habitat.
Our organization hired Pat Trotter, a consultant, to help us design the study. The Dewatto River was chosen for the project because there are few landowners on the river and the habitat is still quite good.
For twelve years, our summer StreamTeam interns collected an inventory of the habitat and gridded the entire system (walking every meter of stream). Initial data collected by the interns in 1998-99 helped to select eight tributaries to the Dewatto for the study.
The study consists of three test streams in the Dewatto System: Shoe Creek, Ralph Creek and Trib 8. As in any study we must have streams to measure our success against. Therefore, there are also five control streams: White, Oak , Alder, Cutthroat and Huson.
When we initiated the study, we measured summer stream flow (pool & riffle surface area, etc.) to calculate the potential habitat available for juvenile coho. Once we knew how many juvenile coho each stream could support, we calculated how many adult coho each stream would need to feed that number of juveniles.
With target numbers for each stream (target number being the adult salmon carrying capacity based on the amount of available habitat), we decided that the three test streams would be supplemented with additional salmon carcasses (either 5x, 10x, or 30x) the adult target numbers. This decision was based on what we understand about Wild Salmon ecosystems as a whole.
We know that 137 species either directly or indirectly depend on Wild Salmon. A direct relationship would be predatory. For instance, an eagle eating a salmon. Whereas an indirect relationship would be the rat eating the salmon carcass, and then the eagle eating the rat. Since we know that other animals rely on carcasses, we are trying to determine what is necessary for balance in the ecosystem; whereby the stream supports the ecosystem as a whole, as well as, produces healthy smolts.
In the Fall, we conduct spawner surveys. We do this to determine how many adults escaped up the streams, and to keep track of where they were spawning.
When the Coho run has ended, we add carcasses to the three test streams. Each stream receives its increased adult target number. On average, we add about 1,500 -2000 Coho carcasses to our test streams. We then survey these streams afterwards to see how many carcasses have disappeared each week due to water flow or scavengers.
As noted above, we often see signs of nature at work, such as carcasses that have been moved up onto the stream banks and other indicators of bears, weasels, raccoons, hawks, eagles, etc. feeding on carcasses. We also sample six fish from each stream for evidence of marine derived nutrients.
In the Spring, we install smolt traps as part of our ongoing monitoring of the study. We do this in partnership with technical assistance from Washington Department of Fish and Wildlife on all of our study streams.
We measured lengths & weights of coho smolts every year (until 2011) as well as measuring the cutthroat and steelhead we catch in the traps. This was a twelve-year study that we hoped will help answer the question: How many Coho adults are needed to support a healthy ecosystem?