Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

Evaluation of the Addition of Inorganic Nutrients and Stream Habitat Structures in the Keogh River Watershed for Steelhead Trout and Coho Salmon

Bruce R. Ward, Donald J. F. McCubbing, and Patrick A. Slaney


Abstract.—Positive numerical responses in steelhead Oncorhynchus mykiss and coho salmon O. kisutch juvenile abundance and size, smolt yield, and smolts per spawner were obtained from watershed restoration in the Keogh River on northern Vancouver Island, British Columbia. Annual increases coincided with treatment and were compared with data from an untreated neighboring watershed (Waukwaas River). The steelhead population, now apparently capable of thriving, was below replacement recruitment prior to the addition of inorganic nutrients and instream habitat structures, the key components of several restoration activities. Annual increases in summer densities of steelhead juveniles were recorded as the rehabilitation treatments progressed from 1997 to 2000. Estimation of steelhead parr densities indicated a 3.8-fold increase over pretreatment or internal untreated values; increases in sites with both inorganic nutrient briquettes and habitat structure additions were 2.5–1.9 times higher than sites with nutrient additions or habitat structures alone. Average size-at-age of juvenile salmonids, by autumn, significantly increased through the years of rehabilitation treatment and compared with fish in the Waukwaas River. Steelhead smolt yield in 2000 increased to 2,338 fish, the highest yield since 1993, but lower than the historical average (>6,000) due to low escapement. Current yield was an improvement over the historic low (<1,000 steelhead smolts, 1998). Coho smolt yield increased to 74,500 or 20% above the historic average (62,000 smolts; 1975–1999), well above the record low counts of 1998 (22,000), but below the historic maximum yield (105,000; 1981). A significant increase in steelhead smolt recruitment at low escapement, from less than 2 to greater than 50 smolts per spawner, was observed over the last four brood years (1995–1998). The assessment now shifts to further benefits to smolt yield, which will require evaluation to 2004.