Effects of Multiple Stressors on Ecological Performance of Early Life Stage Sturgeon

Aquatic contaminants are pervasive in the SFBD, and they are recognized as a potential threat to recruitment of California sturgeon. However, knowledge of the vulnerability of sturgeon to aquatic contaminants is limited. Our goal was to investigate sub-lethal effects of two pesticides (bifenthrin and fipronil) on early life stages of sturgeon, and explore potential synergistic effects with sub-optimal water temperatures. We conducted laboratory exposures of yolk-sac larvae to multiple concentrations of pesticides over 96hrs to identify concentration-dependent impacts on growth, motor-coordination, and activity levels. We saw greater sensitivity in White Sturgeon (Acipenser transmontanus) than in Green Sturgeon (A. medirostris), yet both displayed marked loss of motor-control and reduced activity after three days at the highest exposure concentrations (above environmentally relevant thresholds). These effects were magnified when fish were exposed to bifenthrin at cold temperatures (12C). After the exposure period, fish were allowed to recover in freshwater then tested for ecologically relevant carryover effects. We evaluated thermal tolerance, swimming performance, metabolic rates, and/or foraging behavior, yet saw limited evidence of long-term impacts from aqueous pesticide exposure at the larval life stage. We found that sturgeon may be resilient to environmentally relevant exposure levels of these pesticides under short-term exposure conditions, and more resilient than other species of fishes commonly used for aquatic toxicity testing. Future work would be valuable to address other avenues of exposure (i.e.: ingestion, contaminated sediments), and to consider effects of exposure at older life stages, longer exposures to more persistent contaminants, and the effect of maternal transfer of contaminants on survival and development of embryos and larvae. This increased knowledge about sturgeon responses to common contaminants will allow for more targeted management of the species and their habitats.