Semester

Fall

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Wildlife and Fisheries Resources

Committee Chair

Brent Murry

Committee Member

Caroline Arantes

Committee Member

Tyler Gross

Committee Member

Katherine Zipfel

Abstract

Since their introduction to US waters, Silver Carp (Hypophthalmichthys molitrix) and Bighead Carp (H. nobilis) have rapidly spread throughout the Mississippi River basin and its major tributaries, but their invasion has stalled within the Ohio River. Recent research has suggested this slowed spread could be due to a lack of suitable nursery habitat in the Ohio River, affecting recruitment of invasive carp. This study aims to characterize the habitats juvenile carp are utilizing by investigating three main lines of inquiry: that juvenile carp habitat use is limited by (1) the flow regime of the Ohio River and its tributaries, including (1a) landscape-scale flushing factors in tributary watersheds and (1b) local-scale (within-tributary) refugia from high-flow flushing events, (2) local-scale physical and chemical habitat characteristics, and (3) interactions with the biotic community and food web, including (3a) bottom-up control, (3b) top-down control, (3c) biotic resistance. My study took place in tributaries and embayments of the Ohio River in the J.T. Myers, Newburgh, and Cannelton pools, selected from a dataset of prior juvenile carp survey history (2016-2023). In 2024, I collected a wide range of physical habitat and biotic data from these sites and used publicly available watershed and landcover data to calculate derived habitat variables for analysis. I used logistic regression to identify habitat variables significantly associated with juvenile invasive carp and calculated logistic curves to identify thresholds of significant variables for managers. Of the three hypotheses, the physical habitat hypothesis emerged as the best supported by evidence – both water temperature (accumulated degree days) and turbidity (Secchi depth) emerged as top variables associated with juvenile carp habitat use. In contrast, the flushing/persistence and food web hypotheses were relatively poorly supported, with only the amount of agricultural land use in a watershed and species evenness emerging as having a significantly (negative) association with carp presence. Collecting temperature data in further upstream pools of the Ohio River and applying the thresholds identified in this study could allow managers to identify tributaries that are at “high risk” of juvenile carp invasion, and monitor these closely to improve early detection. Conversely, upstream tributaries that have environmental conditions below these thresholds can be identified as lower priority sites for monitoring, saving managers time and resources.

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