Investigating and interpreting reduced reproductive performance in fish inhabiting streams adjacent to agricultural operations

Previous studies have indicated that fish in agricultural areas have reduced proportions of young of the year (YOY) fish, due to either reproductive dysfunction, increased mortality, or a combination of these factors. The main objective of this research was to identify the potential mechanisms and timing associated with the reduced reproductive performance in agricultural areas. Fish populations were monitored systematically through multiple years to identify peak mortality and risk periods based on agricultural practice and inputs. In previous assessments sculpin species have presented conflicting response patterns, making interpretation difficult. Normal reproductive profiles, growth and mortality were assessed for reference populations of slimy sculpin ( Callus cognatus) to identify the most appropriate window to assess reproductive integrity. Comparisons between spring and fall spawning species in agricultural areas determined the degree of potential impact of exposure to stressors on differing reproductive strategies. Finally the integration of this information collected on episodic mortality, reproductive development and reproductive performance required some consideration of population level impacts. The tools for population level ecological risk assessment are poorly developed, and the theoretical aspect of this thesis focused on trying to integrate the available information, identify the data gaps, and recommend an overall approach to population risk assessment that will be based on information gathered regarding non-point, multiple stressor discharges.