FROM INTRODUCTION TO SPREAD: UNDERSTANDING THE SPATIAL AND RESOURCE ECOLOGY OF SILVER CARP

Author

Tanya Elizabeth Fendler, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2025

Degree Name

Doctor of Philosophy

Department

Zoology

First Advisor

Garvey, James

Abstract

Invasive species are one of the leading causes of biodiversity decline. Managing invaders in freshwater ecosystems is more challenging due to the increased likelihood of multiple introductions, the open nature of many water bodies that facilitate spreading, the time delay between their introduction and the resulting spread or impacts, the difficulty in detecting them, and the numerous human-induced stressors and alterations these ecosystems have undergone. One notorious invasive species within the United States is the silver carp (Hypophthalmichthys molitrix). This large-bodied planktivorous fish native to Eastern China has been found to outcompete native planktivores, alter the abundance and composition of plankton communities, decline native sportfish populations, and cause physical injuries to boaters. Management practices for this invader include expensive electric barriers and deterrents, laborious harvest-removal, and proactive monitoring within adjacent aquatic ecosystems such as the Great Lakes. The primary goal of this dissertation was to enhance our understanding of the resource and spatial ecology of silver carp. The first research chapter estimated chlorophyll-a concentrations across 18 rivers located in the Northern United States and assessed long-term trends and regional patterns. The second research chapter assessed differences in movement and aggregation of silver carp from the Illinois and Lower Wabash Rivers using acoustic telemetry. The third research chapter quantified the survivability of silver carp and other native fish species within ephemeral wetlands and monitored the change in water quality and zooplankton abundance. The final research chapter identified uninvaded regions with suitable habitat for silver carp under several climate change scenarios. Findings from this dissertation revealed that half of the rivers analyzed exhibited a decrease in chlorophyll-a concentrations over the past 38 years. Although this may indicate positive progress in the prevention of silver carp, receiving waters have experienced an influx in algal blooms, potentially making those areas better suited for silver carp. Silver carp were found to travel great distances, including moving between basins, thereby highlighting the necessity for integrated management strategies rather than isolated control efforts within a single basin. Interestingly, silver carp had low survival within ephemeral wetlands. This observation implies that silver carp may not be as well adapted to ephemeral wetlands and backwaters, which are vulnerable to extreme weather events, in comparison to native species. Despite backwaters being ill-suited, Lake Michigan, Lake Superior, and North America overall, will become more suitable for silver carp by 2050, possibly predicting an impending expansion of their range. The outcomes presented in each chapter have several ecological and management implications. First, the increase in suitable habitat coupled with the highly mobile nature of some individuals can lead to rapid range expansion, consequently, negatively impacting the native community in regions outside the Midwest. This, coupled with the already declining trend in primary productivity could result in very different community compositions in the near future. To prevent this, preventative management efforts and funds should be allocated to eutrophic rivers and their receiving waterbodies, rivers located up to 500 km from the invasion front, and rivers anticipated to be highly suitable for silver carp.