Is chemical contamination responsible for the decline of the copper redhorse ( Moxostoma hubbsi), an endangered fish species, in Canada?

Abstract

The copper redhorse (Catostomidae: Moxostoma hubbsi) is an endangered fish species whose worldwide distribution is limited to the St. Lawrence River and three of its tributaries, in Canada. Severe reproductive impairment and lack of successful recruitment reported in this species have been hypothetically associated with water pollution. In order to obtain an initial description of contamination levels in copper redhorse, seven accidentally-killed specimens from the Richelieu River were analyzed for trace metals, organochlorine pesticides, chlorobenzenes, PAHs, PCBs, dioxins and furans. Fish varied between 9 and 33 years of age, which corresponds to mature individuals. The levels of contaminants analyzed in different body tissues were close to and often lower than levels reported in other catostomid fish species from nearby locations within the St. Lawrence River basin. Concentrations of total mercury, cadmium and co-planar PCBs increased with fish age. The types and concentrations of contaminants found suggested that the Richelieu River spawning population of copper redhorse would migrate and spend time in the St. Lawrence River. Concentrations of many contaminants were often highest in gonadal tissues, but levels were much lower than reported in the literature as causing reproductive impairment or egg and fry mortality in fish. Further research is needed to assess the potential link between contaminants and reproductive failure in this endangered fish species.