Monitoring individual- and population-level effects of fish populations along a gradient of agricultural inputs

Since 1999, a variety of aquatic research studies have been focussed in a small area of North-western New Brunswick (Canada) where intensive potato production provides a gradient of agricultural inputs into adjacent waterways. Overall, an effects-based approach was used to examine individual- and population-level endpoints including survival and reproduction of slimy sculpin (Cottus cognatus) in this potato farming belt. Systematic sampling of fish densities and size structure was conducted over multiple years at various sites along the agricultural gradient in an attempt to identify the timing of mortality events and the relative effects of potential stressors (e.g. temperature, sedimentation). A combination of lethal and nonlethal methods provided a suitable study design due to repeated sampling in relatively small areas of river. Sculpin demonstrated increased individual growth, reduced reproductive potential (gonad size, fecundity, nest numbers and sizes), and increased variability relative to upstream sites (i.e. no agricultural influence). Young-of-the-year (YOY) sculpin downstream of agricultural inputs were longer and heavier than those collected at upstream non-agricultural sites. Precipitation and water temperature were both negatively related to % YOY in the agricultural areas but not in the upstream forested sites. This summary of slimy sculpin research studies provides a current 'state of the environment' for this system from the organism level and aids in the development of methods to define cause-effect relationships with nonpoint source pollution.