The effects of salinization on freshwater fishes of the Northern Great Plains

Abstract

Salinization poses a threat to many inland aquatic ecosystems. Therefore, it is important to understand the potential implications of salinization on aquatic systems. Saline water bodies are prevalent in the Northern Great Plains of North America—an area that includes portions of Alberta, Saskatchewan, and several northern states in the United States. In this area, saline water bodies provide an environmentally important habitat for a variety of species. Salinization, both natural and anthropogenic, is predicted to increase in the Northern Great Plains in the future, but the potential effects on aquatic organisms remain largely unknown. To investigate these potential impacts, I first established lethal levels of salinity exposure in fathead minnows (Pimephales promelas), northern pike (Esox lucius), and walleye (Sander vitreus). This experiment also gave me a framework for determining relevant concentrations with which to test the effects of sub-lethal salinity exposure on fathead minnows. After deciding appropriate levels, I exposed minnows to one of three sub-lethal salinity concentrations crossed by one of three alarm cue concentrations—an indicator of imminent predation risk. I found that salinity reduced the overall intensity of antipredator behaviour in the highest salinity concentration, and also eliminated threat-sensitive responses at the intermediate salinity concentration. I then tested the effects of salinity on reproductive endpoints, both egg-based and behavioural, in fathead minnows. I found impacts on egg-based endpoints at all salinity levels, even the relatively low 1000 parts per million (ppm) concentration. I also found significant reproductive behaviour modification in the highest salinity treatment. I was then interested in determining an adequate acclimation point at which reproductive endpoints of minnows held in saline water matched those of minnows held in dechlorinated tap water. My data suggest that the acclimation point is approximately 14 weeks in 1000 ppm salinity, though it should be noted that my scope of inference may be limited by small sample sizes. Finally, I investigated second generation effects of minnows spawned, hatched, and reared in low-level salinity. I found no effect of salinity on morphology or antipredator responses.