Influences of Stocking Salmon Carcass Analogs on Salmonids in Klickitat River Tributaries, 2001-2005 Completion Report.

摘要

This report describes the work completed by the Yakama Nation Fisheries Program (YNFP) in the Klickitat subbasin in south-central Washington under BPA innovative project No.200105500--Influences of stocking salmon carcass analogs on salmonids in Columbia River Tributaries. Salmon carcasses historically provided a significant source of marine-derived nutrients to many stream systems in the Columbia basin, and decreased run sizes have led to a loss of this nutrient source in many streams. Partners in this project developed a pathogen-free carcass analog and stocked the analogs in streams with the following objectives: restoring food availability to streams with reduced anadromous salmon returns; mimicking the natural pathways and timing of food acquisition by salmonids; minimizing unintended negative ecological effects; and increasing the growth and survival of salmonids. In the Klickitat subbasin, carcass analogs were stocked in two streams in 2002 and 2003; a third stream was used as a control. Salmonid fish abundance, growth, and stomach contents were monitored in all three streams before and after carcass analog placement. Fish, invertebrate, and periphyton samples were also collected for stable isotope analysis (to determine if nutrients from carcass analogs were incorporated into the stream food web). Water quality samples were also collected to determine if nutrient overloading occurred in streams. Significant differences in growth were found between fish in treated and untreated stream reaches. Fish in treatment reaches exhibited higher instantaneous growth rates approximately one month after the first carcass analog stocking. Stomach contents sampling indicated that salmonid fish routinely consumed the carcass analog material directly, and that stomach fullness of fish in treatment reaches was higher than in untreated reaches in the first few weeks following carcass analog stockings. No significant differences were detected in fish abundance between treatment and control streams after carcass analog stocking. Stable isotope analysis provided some evidence that nutrients (primarily nitrogen) were incorporated into periphyton and invertebrates, although this evidence is not strong. No significant differences in water quality were observed between treatment and control streams after analog stocking. Although no significant changes were observed in fish abundance, this study does provide evidence that carcass analogs provide a viable and potentially useful alternative to stocking salmon carcasses. The analogs provide a direct food source to salmonids, and show some potential for providing nutrients for stream food webs. They can also increase stomach fullness and growth rates of individual fish. This nutrient source may very well improve individual fish condition sufficiently to improve overwintering or smolt survival. Further refinement of stocking densities and timing, treatment duration, and tailoring analog placement to individual stream characteristics (such as channel confinement and flow) will further improve the usefulness of carcass analogs.