Chronic Exposure to Polynuclear Aromatic Hydrocarbons in Natal Habitats Leads to Decreased Productivity and Fitness of Pink Salmon Populations

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The immediate and delayed effects of embryonic exposure to low levels of polynuclear aromatic hydrocarbons (PAHs) reduce survival to maturity by 50% in exposed pink salmon populations, indicating that chronically exposed populations should rapidly decline to extinction. However, density dependence may prevent or delay extinction. This report measures the effects of chronic exposure on a simulated pink salmon population. The simulation uses empirically derived survival functions based on 70 years of observations of a single population. The survival functions are combined with the effects of embryonic exposure to PAHs on survival to determine how chronic exposure affects population productivity (median number of returns), fitness (median returns-per-spawner) and the probability of extinction over 35 generations. The PAH effects were observed among fish rearing in the same watershed as the modeled population. The resulting models predict that at low levels of exposure, density dependence compensates for reduced productivity, buffering the population against extinction. However as toxicity increases, random environmental variation overcomes this buffering effect and extinction probability increases. For example, exposing 100% of the population to aqueous PAH concentrations of 18 parts-per-billion leads to an 80% decrease in population productivity and an 11% probability of extinction within 35 generations. Increasing the relative toxicity of the exposure by 60% results in a 100% probability of extinction. These data demonstrate that chronic contamination of natal fish habitats at PAH concentrations near statutory limits can significantly reduce population productivity and stability.