Enhanced Incubation Success for Kokanee Spawning in Groundwater Upwelling Sites in a Small Idaho Stream

—Kokanee (Oncorhynchus nerka lacustrine sockeye salmon) spawned in groundwater upwelling in the North Fork of the Payette River, Idaho. Intragravel water temperatures in groundwater-influenced redds exceeded surface flow water temperature by 2.4–2.68C. In redds without groundwater influence, intragravel and water column temperatures did not differ by more than 0.28C. Although redds constructed in upwelling sites contained significantly more fine sediments (,0.83 mm) and were constructed in areas of significantly lower surface water velocities than redds not influenced by upwelling, preemergent survival of fry from redds in upwelling sites (84%) significantly exceeded that from redds in other areas (66%). Higher incubation temperatures at upwelling sites accelerated rates of development, protected embryos from freezing, and may increase survival of fry recruiting to Payette Lake. Current knowledge on effects of groundwater or spring upwelling on salmonid incubation success is limited (Hansen 1975; Carline 1980; Sowden and Power 1985). Upwelling may enhance embryo survival by providing a more stable thermal environment and increasing water exchange rate past embryos (Bjornn and Reiser 1991). Sheridan (1962) documented warmer winter temperatures at upwelling sites but concluded that most intragravel dissolved oxygen downwelled from the stream. High fractions of fine sediments reduce embryo survival (Phillips et al. 1975; Hausle and Coble 1976; Tappel and Bjornn 1983) and size of emerging fry (Shumway et al. 1963; Koski 1966; Phillips et al. 1975; Tappel and Bjornn 1983). However, incubation success and fry quality may not depend on substrate quality in areas of groundwater upwelling with sufficient (.6.0 mg/L) dissolved ox* Corresponding author: [email protected] 1 Present address: Maine Department of Inland Fisheries and Wildlife, 328 Shaker Road, Rural Route 1, Gray, Maine 04039, USA. ygen (Sowden and Power 1985; Bjornn and Reiser 1991). Use of spring or groundwater upwelling sites for spawning has been reported for bull trout Salvelinus confluentus (Heimer 1965), sockeye salmon Oncorhynchus nerka (Lister et al. 1980; Lorenz and Eiler 1989), pink salmon O. gorbuscha (Krueger 1981), rainbow trout O. mykiss (Sowden and Power 1985), and brook trout S. fontinalis (Hansen 1975; Webster and Eiriksdottir 1976; Fraser 1985; Snucins et al. 1992; Curry et al. 1994). However, we found no studies that reported the use of upwelling areas by spawning kokanee (lacustrine sockeye salmon), and none compared incubation success of salmonids that spawned in upwelling sites with that of cohorts that spawned in areas unaffected by groundwater. In this study, we assessed the use of groundwater upwelling areas by spawning kokanee. We compared preemergent survival, water depth and velocity, and fine sediment composition of kokanee redds in upwelling areas with the same variables in redds that lacked evidence of groundwater inflow.