Approaches for Determining Effects of Pollution on Fish Populations of Puget Sound

Abstract

Puget Sound is a large marine and estuarine ecosystem in Washington State that serves as the habitat for a number of recreationally and commercially important species of groundfish and Pacific salmon Onchorhynchus spp. Over the past several decades, the human population of the Puget Sound drainage basin has increased substantially, resulting in increased habitat degradation and chemical pollution. There is now a body of evidence showing that groundfish and salmon in Puget Sound are experiencing a range of biological effects from chemical contaminant exposure, including impairment of several stages in the reproductive process, increased susceptibility to pathogens resulting from altered immune competence, and development of toxicopathic diseases. Preliminary studies suggest the potential for reduced survival of fish from urban areas of Puget Sound resulting from increased infectious and idiopathic diseases. The question that now must be addressed is whether contaminant-related reductions in reproductive and survival rates are sufficient to affect fish abundance in Puget Sound. In the current study, the potential impact of contaminant-related mortality and reproductive impairment on the population growth rate of English sole Pleuronectes vetulus was examined by simulation modeling. An initial Leslie matrix population model was constructed for investigation of contaminant effects. The adult mortality rate for English sole in Puget Sound was estimated from recent historical data. Age-specific fecundity was determined from previously collected English sole ovary samples. Existing data on the effects of contaminants on reproduction, including impaired gonadal development, reduced spawning ability, and decreased egg and larval viability, were incorporated into the fecundity component of the model. The influence of density-dependent population regulation on model results was also examined. Results suggest that declines in the fecundity component of the model, like those observed in field studies of fish from contaminated sites such as the Duwamish Waterway and Eagle Harbor, could substantially decrease the population growth rate (r) if density dependence is weak or moderate, Estimated declines in r are comparable in magnitude to those associated with typical levels of commercial fishing pressure, However, a compensation for loss of recruits due to contaminant effects is observed if strong density-dependent population regulation is assumed.