Feasibility of Nutrient Enrichment to Reclamation Reservoirs to Enhance Biological Productivity for Reintroduced Anadromous Salmonids
* Will fertilizing an unproductive oligotrophic Reclamation reservoir where fish passage facilities are being installed enhance and sustain a viable and abundant food base for re-introduced anadromous salmonids?
* Will an oligotrophic reservoir that presently supports a sparse resident fish population be able to sustain a re-introduced population of anadromous fish like sockeye salmon, or will re-introduced anadromous salmonids negatively impact the system if reservoir fertilization does not occur?
Need and Benefit
Cle Elum Lake, Washington, in the Upper Yakima River Basin, is part of the Yakima Project. It is operated to meet downstream water delivery needs, flood control, and instream flows for fish. Historically, the Yakima Basin supported large runs of anadromous salmonids. The Cle Elum River above Cle Elum Lake historically supported several anadromous salmonid species and has the potential for supporting anadromous salmonid populations again. There are no permanent upstream or downstream fish passage facilities at any of the storage projects in the Yakima River basin.
Reclamation assessed the feasibility of providing upstream and downstream fish passage at the five major Yakima Project storage dams and determined that the watershed above Cle Elum Lake contained at least 29.4 miles of good quality habitat that could be used by anadromous salmonids if fish passage were provided. An interim fish passage structure for juvenile outmigrants was constructed at Cle Elum Dam in 2005. Sockeye salmon are being considered for reintroduction into the Cle Elum watershed. Sockeye salmon spawn in rivers, but the fry migrate downstream soon after emerging from the gravel to rear in lakes for most of their juvenile life stage. Since juvenile sockeye salmon rear in lakes, it is important that they have an adequate food supply there.
Cle Elum Lake is oligotrophic, with a very sparse zooplankton population. Marine-derived nutrients from salmon carcasses historically contributed substantially to the productivity of river and lake systems, including production of zooplankton, but this source of nutrients is no longer available. Lake fertilization has been employed successfully in some British Columbia lakes to increase and enhance the zooplankton food base for rearing sockeye salmon. It is important to determine if the present sparse zooplankton population of Cle Elum Lake can be enhanced through fertilization to provide an adequate food supply for sockeye salmon and improve the opportunity for success of salmon reintroduction efforts.
The Yakima Dams Fish Passage Phase 1 Assessment Report (2003) stated that an adequate monitoring and evaluation program must be an integral part of any fish passage and restoration program. Therefore, a comprehensive limnological research study on Cle Elum Lake was funded in fiscal years (FY) 2004 and 2005 by the Pacific Northwest (PN) Regional Office to determine if the food base would support anadromous salmonids. Rigorous research on the effects of fertilizing an unproductive lake will broaden our understanding of this management option for enhancing the productivity and food base to support reintroduced anadromous salmonids.
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