Fish Community Structure and Diet Responses to Newbury Weirs in a Low-Gradient River

Abstract

Restoration projects are often implemented to address specific issues in the environment. Consequences of a restoration project, if any are measured, typically focus on direct changes to the projects focus. However, changing habitat structure likely results in changes to the environment that affect the communities living there. Rock weirs have been used for channel stabilization in many midwestern rivers. Previous research in a southern Illinois river found that weirs benefitted aquatic macroinvertebrate and riparian bird communities by enhancing habitat heterogeneity and insect emergence production. We hypothesized that fishes would also benefit from weirs through enhanced habitat and food availability. We collected fishes in the Cache River in southern Illinois using hand nets, seines, and electroshocking at sites where weirs had been installed and at non-weir sites. Gut contents were identified and individual food items measured. Fish species richness, but not diversity, was higher at weir sites. Fish communities also differed between site types, with benthic feeders characterizing weir sites. Gut content biomass and abundance differed among fish guilds but not between weir and non-weir sites. Fishes from both site types selected for prey taxa predominately found at weirs. Differences between site types were not always captured by univariate metrics, but connecting fish prey to habitat suggests a reach-scale benefit for fishes through increased abundance of favored prey and enhanced prey diversity. Additionally, given the paucity of rocky substrata in the river as a whole, rock weirs enhance fish species richness by providing habitat for less common benthic species.

Evaluating effectiveness of restoration to address current stressors to riverine fish

“…For example, density was measured as a response variable for goals such as, ”improve connectivity and access to habitats” or ”increase the amount of suitable habitat available” to ”support greater fish abundance and production” (e.g., Koljonen et al., 2013; Stoller et al., 2016). Richness was measured as a response variable for goals such as, ”enhance habitat heterogeneity and food availability to benefit fish communities” or ”determine if reconnection can restore fish community structure” (e.g., Bonjour et al., 2018; Rourke et al., 2019). These count metrics were likely to have been the most used ecological indicators because they are more feasible to estimate than acquiring detailed data on resource use or demography in response to changes in habitat.…”