Fraser River sockeye salmon: data synthesis and cumulative impacts

supply or water temperature. Unless interbasin transfers of water occur, effects onsockeye nursery lakes are unlikely.o Urbanization creates impervious surfaces that perturb natural streamflow patterns,altering the quantity, quality and accessibility of riparian habitats, and impairing waterquality; all of these effects can potentially affect sockeye egg-to-fry/smolt survival.o Agriculture can affect spawning and rearing habitats by physically altering streamchannels, riparian zones and floodplains; direct removal of surface and ground water, anddegradation of water quality.o Water withdrawals for industrial, commercial, domestic and agricultural uses canreduce access to sockeye spawning, rearing and migratory habitats, and also affect theirquality.MacDonald et al. (2011) conducted a comprehensive inventory of contaminants, or chemicalsof potential concern (COPCs), within the Fraser Basin. Their inventory includes contaminantsoriginating from point sources (e.g., pulp and paper mills, sawmills, wood preservation facilities,cement and concrete plants, seafood processing facilities, mines, oil and gas developments,storage and shipping facilities, contaminated sites and spills, municipal wastewater facilities,landfills, salmonid enhancement facilities), non-point sources (e.g., runoff from forestmanagement areas, agriculture operations, municipal stormwater and linear developments) andatmospheric sources (e.g., forest fires; volcanoes; emissions into the air from vehicles, industries,and agriculture; long range transport of atmospheric pollutants). Some of these sources ofCOPCs could potentially affect spawning and rearing habitats, while others are restricted tomigratory corridors. MacDonald et al. (2011) systematically whittled down their long list ofCOPCs through analyses of contaminant pathways and exposures relative to thresholds affectingsockeye, as described in the Executive Summary of their report.The spawners in one brood year can potentially affect the total life cycle productivity (adultrecruits per spawner) of the next three brood years. If these effects are negative, then this iscalled delayed density dependent mortality. As described in Peterman et al. (2010; section4.7), the proposed mechanisms are that a large number of spawners in one year will produce alarge number of fry the subsequent spring, which increases competition among juvenile salmonfor limited food resources in the rearing lake, increases incidence of disease in salmon, and/orleads to increased predation on juvenile salmon in the rearing lake or elsewhere in the life cycle.Conversely, declining abundances of sockeye result in less nutrients being transferred frommarine to freshwater ecosystems, with potential negative effects on both subsequent generationsof sockeye and other ecosystem components (reviewed by Nelitz et al. 2006).40