Fraser River sockeye salmon: data synthesis and cumulative impacts

o were generally worse during the last 2-3 decades (as compared to prior decades) for mostof the non-Fraser stocks;o showed a major improvement for some Fraser stocks (particularly Harrison, Chilko,Adams) that led to large returns in 2010.4.2 Stage 1: Incubation, Emergence and Freshwater RearingThe stage covers sockeye salmon from egg to the beginning of their outmigration to the ocean.4.2.1 Plausible mechanismsAs shown in the conceptual model (Figure 3.3.-1) plausible mechanisms affecting Stage 1include: 1) Fraser watershed habitat conditions (particularly the effects of forestry, mining,hydroelectricity, urbanization, agriculture, and water use); 2) delayed density dependentmortality; 3) predation, 4) disease and 5) climate change. There are cause-effect mechanisms bywhich each of these factors could at least potentially affect sockeye egg-to-fry, or egg-to-smoltsurvival rates, as described below.The potential effects of Fraser watershed habitat conditions on Stage 1 are discussed in Nelitzet al. (2011; section 3.0), and are summarized below:o The activities associated with forestry (particularly road construction, stream crossings,and upslope harvesting) can alter the amount and timing of delivery of water andsediment to streams, potentially affecting spawners, eggs and juveniles. The mountainpine beetle outbreak in BC’s Interior (due in part to warmer winters caused by climatechange) has led to extensive salvage logging, expanding the area potentially affected byforestry. Unlogged watersheds with mountain pine beetle have hydrological patternsintermediate between a mature forest and a clearcut.o Mining can potentially affect sockeye spawning through permanent loss of habitat,disruption of the stream bed, sedimentation on incubating eggs, or contamination by aciddrainage, heavy metals and other toxic substances.o Large scale hydroelectric facilities (in particular the Bridge/Seton River power projectand Alcan’s Kemano project on the Nechako) can potentially affect Fraser sockeyethrough physical barriers to migration, increased stress/disease, greater vulnerability topredators and direct turbine/spillway mortality.o Smaller scale hydro facilities, including Independent Power Projects or IPPs generallydivert water from fishless stream channels, but can potentially affect downstreamspawning areas and migration corridors through changes to total gas pressure, gravel39