CHEMICAL CONTAMINANTS, LIVER-DISEASE, AND MORTALITY-RATES IN ENGLISH SOLE (PLEURONECTES VETULUS)

Previous studies have shown that exposure to chemical contaminants is associated with a variety of disease conditions in feral fish. However, relatively little is known about the effects of toxicopathic disease or other types of impairment associated with chronic exposure to environmental contaminants on fish mortality rates. In this study, annual mortality rates were estimated in English sole (Pleuronectes vetulus) from heavily and minimally contaminated areas in Puget Sound (Washington state), and in sole with and without selected hepatic lesions, including neoplasms. Mortality rates were determined using catch curve analysis and linear regression techniques. For English sole 3 yr of age and above from urban and non-urban areas of Puget Sound combined, the annual mortality rate was 0.38. This estimate is similar to published mortality rates for English sole from northern Puget Sound and other flatfish species from the North Sea, Grand Banks, and western Canada. Mortality rates in sole from heavily contaminated sites or in sole with toxicopathic liver lesions were not significantly higher than those for English sole from Puget Sound as a whole. These findings suggest that although toxicant-related death due to disease or other impairment may contribute to mortality rates in English sole, at least in older animals, its impact appears to be overridden by other factors that could deplete English sole populations, such as fishing pressure, predation, or fluctuations in food supply. The major impact of chronic exposure to environmental contaminants may be on reproductive capacity, egg and larval viability, and survival of juveniles rather than on survival of adults.