Potential Effects of Contaminants on Fraser River Sockeye Salmon

7.4.3 Temporal Coverage <strong>of</strong> Environmental Data• Data on the concentrations <strong>of</strong> chemicals <strong>of</strong> potential concern in surface waterand, to a lesser extent, sediments were available for many <strong>of</strong> the areas used asmigration corridors by sockeye salmon. However the temporal coverage <strong>of</strong>environmental data in these areas was <strong>of</strong>ten limited and was not consistentacross the study area. These limitations rendered uncertain the comparisons <strong>of</strong>exposure for the various sockeye salmon conservation units during smoltoutmigration and adult upstream migration.• While the requisite data may be available, information on the timing andspecific habitat use by each sockeye salmon stock during downstreammigration were not located. This limitation necessitated adoption <strong>of</strong> theassumption that outmigration timing and habitat use within the lower FraserRiver was similar for all stocks, with the exception <strong>of</strong> the Harrison River stock.This assumption could result in erroneous conclusions regarding the role <strong>of</strong>contaminants in the decline <strong>of</strong> sockeye salmon if the various stocks havedifferential exposure to contaminants.7.4.4 Availability <strong>of</strong> Data on the Contaminant and Ancillary Variables• The assessment <strong>of</strong> exposure <strong>of</strong> sockeye salmon to contaminants <strong>of</strong> potentialconcern relies on the comparison <strong>of</strong> observed contaminant concentrations inenvironmental media (e.g., surface water and sediments) to environmentalbenchmarks. As many contaminants are influenced by the chemistry <strong>of</strong> themedia, ancillary information on water quality and/or sediment quality is <strong>of</strong>tenneeded to accurately characterize exposure. That is, data on ancillary variables(i.e., water hardness, temperature, and pH) are <strong>of</strong>ten required to calculatesample-specific benchmarks (i.e., toxicity screening values and/or toxicityreference values). The variables that fall into this category include ammonia,fluoride, aluminum, copper, lead, manganese, and nickel. Therefore, spatialand temporal coverage <strong>of</strong> ammonia, fluoride and some metals was limited tothose stations and samples only for which the ancillary parameters were alsomeasured.• Calculation <strong>of</strong> the water quality index (Saffran et al. 2001) requires at leastfour independent measurements <strong>of</strong> at least four water quality variables for eachperiod <strong>of</strong> time. As data on water quality variables were not consistent spatiallyor temporally for all stocks, the variables and samples used in the indexcalculations had the potential to be inconsistent within and between stocksfrom year-to-year.127