Extensive coal mining operations within the Elk River Basin from the late 1800s to present has contributed high concentrations of selenium, nitrate, sulphate, and cadmium to the Kootenai River watershed than would be expected under unimpacted conditions. Selenium is considered the pollutant of primary concern due to its toxicity and propensity to bioaccumulate in the food web. While selenium is an essential micronutrient in small concentrations, fish exhibit a narrow window between essentiality and toxicity. The selenium contamination of the Kootenai River ecosystem has become an international concern and is suspected to be contributing to the system’s observed burbot population decline. Since current burbot restoration efforts within the Kootenai River ecosystem are focused on improving natural recruitment, and because of the known negative impacts of excess selenium on larval fish development, knowledge of the impacts of selenium on burbot embryo and larval performance is paramount. Thus, the survival and growth performance of embryos and larvae from a captive burbot population receiving only dietary levels of selenium were compared to the survival and growth of wild Kootenai River origin embryos and larvae. The average selenium concentration in the Kootenai River origin eggs, 11.33 mg/kg of dry weight (dw), was 2.5 times higher relative to a reference population in Northwestern Ontario, 4.55 mg/kg dw, and 7.8 times higher than the captive burbot population, 1.45 mg/kg dw. Despite the relatively high selenium concentration of the Kootenai River origin eggs, there was no statistical difference in embryo or larval survival relative to the captive population. However, eye deformities and edema, both classic symptoms associated with selenium toxicity, were observed only in Kootenai River larvae. While these deformities do not directly lead to death, these morphometric irregularities probably contribute to overall lower fitness. Thus, the observed selenium associated deformities in the Kootenai River larval burbot may contribute to low recruitment in the wild population of Kootenai River burbot. Future efforts should focus on identifying the concentration of selenium in burbot eggs that lead to embryo/larval mortality.
This research was funded through BPA2002-002-00 (The Kootenai River Habitat Restoration Project).