Monitoring Temporal Trends in Catostomidae Larvae in Large Sized River Tributaries

Large river ecosystems can support a complex network of tributaries that provide optimal habitat for fish reproduction. Anthropogenic alteration of rivers and tributaries has been shown to have adverse effects on river fish communities, but few studies have focused on the effects river regulation may have on the reproduction of native suckers (Family Catostomidae). In this study, I evaluated differences in biotic and abiotic factors associated with catostomid reproduction between tributaries of an altered and free-flowing river. I conducted ichthyoplankton sampling using drift nets and larval push nets in tributaries of the Illinois River, which is regulated for navigation, and the lower Wabash River, which is free-flowing and not used for navigation. I sampled three tributaries of the Illinois River (Mackinaw River, Sangamon River, and Spoon River) and three tributaries of the Wabash River (Little Wabash River, Embarras River, and Vermilion River). I collected catostomid larvae from each system twice each month from April until September during 2016 – 2018. I analyzed total relative abundance, catch per unit effort (CPUE), and trends in abiotic variables such as discharge, water temperature, gauge height, dissolved oxygen, pH, and conductivity between the two systems. I also created multiple logistic regression models to determine which variables increased probability of sampling catostomid larvae. For all sample years, the Wabash River tributaries contributed more catostomid larvae than the Illinois River tributaries. My results indicate that the Wabash River system is more influenced by gauge height and water temperature whereas the Illinois River system is more influenced by dissolved oxygen and discharge. Within each system, the tributary that had the highest discharge levels also consistently had the highest number of catostomid larvae. Multivariate analysis of variance also revealed that there was a significant interaction between tributary and all abiotic variables. With a few exceptions, I found that mean CPUE of larval catostomids was greater with larval push nets than drift nets. Drift nets were still an effective gear for sampling and should be continued to be used to collect larvae, especially in shallow habitats that preclude the use of larval push nets. The multiple logistic regression models showed that increasing discharge and water temperature increased probability of larvae capture for the Illinois River tributaries. The model for the Wabash River tributaries had all variables except discharge as significant variables for increasing probability of larvae capture. Overall, my results indicate that there are differences in water quality and catostomid reproduction between the Wabash and Illinois River system. However, specific tributaries contribute the majority of larvae to each system. Assessments of catostomid reproduction should target tributaries in each system with the highest discharge values and use both gear types to effectively sample larval fishes across tributary habitats