| Summary: | Pacific salmon (Oncorhynchus spp.) life cycles involve completion of several developmental stages including the alevin stage. As alevins, sockeye salmon are found within freshwater gravel redds where they utilise yolk sacs for nutrition, growth and development. Flow mediated scour events pose a common threat of destruction to both redds and fragile alevins during a several month period of winter incubation. However, to date, there is very little research on the impacts of early forced emergence of alevins. Using sockeye salmon (Oncorhynchus nerka) as a model, simulated elevated discharge event (SEDE) experiments were conducted to examine the relationship between sockeye alevin development, SEDE exposure and alevin survival. Following five weeks of SEDE experiments, survival rates were found to be significantly correlated to both alevin developmental stage and length of elevated discharge exposure. SEDE experiments were followed by experiments designed to investigate the ecological competence level of alevins following forced early dislodgement. Repeated tests during a five week interval immediately following egg hatch indicated that alevins subjected to SEDE exposure took longer than unexposed alevins to rebury in gravel. Alevins exposed to SEDEs took longer to rebury as they developed, but increased their overall ability to rebury. Neither SEDE exposed or unexposed alevins exhibited abilities to initiate exogenous feeding given forced, early emergence. Survival rates of sockeye salmon alevins both during and after SEDE testing increased significantly with advances of developmental stage. Older, larger alevins also exhibited improved performance in responding to ecological challenges presented in laboratory experiments. Knowledge gained from this research has practical implications for water managers and suggests that: (a) the probability of scour induced mortality of both unhatched eggs and alevins is likely similar up to at least 3 weeks after egg hatch, (b) survival rates and ecological competence of alevins has improved significantly by four weeks following egg hatch, and (c) survival of alevins forced into an epibenthic or water column environment as late as one week before volitional emergence is unlikely to differ greatly from that of unforced emergent fry.
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