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Water quality in the lower Fraser River Basin : a method to estimate the effect of pollution on the size of a salmon run Brox, Gunter Herbert

Abstract

Water quality studies conducted in the recent past in the Lower Fraser River Basin indicated that locally some high pollution levels exist. With further urbanization and industrialization of the Vancouver region an increase in waste loadings and a degradation of water quality can be expected if no strict pollution control is applied. Of particular concern are biologically undegradable substances such as heavy metals and poly-chlorinated hydrocarbons. They accumulate in the sediments of the river and the estuary and become concentrated in organisms of the food chain. Pollution is a gradually occurring process. Anticipation of potential problems is important for the decision maker responsible for water quality management. The Fraser River supports one of the largest salmon runs of the world and is abundant with other commercially and recreationally valuable fish. Salmon are very sensitive to pollution and could disappear from the Fraser river system as they already have from many other major rivers if pollution levels become too high. The Fraser River estuary has the function of a bottleneck. Adult salmon enter the river to migrate upstream to their spawning grounds, and juvenile salmon stay in the estuary for a while to acclimatize themselves to the saline environment. In this thesis a method is presented to simulate the effects of potential pollution on the size of a salmon stock. A model which uses data from various life stages of a particular sockeye salmon run in the Fraser system is developed. Uncertainties due to environmental fluctuations are accounted for. Using this model the effects of an increase in mortality rate in two stages of the sockeye salmon life cycle on adult return numbers are studied. The analysis showed that at a certain mortality rate chances are that the stock might not be able to recover. In light of a planned salmon enhancement program to increase salmon stocks in various Pacific rivers, the fact that decreasing water quality could counteract all enhancement efforts should be a warning signal to the decision makers. The development of a water quality index to predict future conditions is recommended and a possible procedure to relate water quality parameters to an increase in mortality rate is sketched out.

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