Book Description

Informing monitoring and surveillance efforts for invasive species is crucial for effective management to minimize negative ecological, economic, and social impacts. Management responses to the invasion of silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis)--collectively termed bigheaded carps--in the upper Illinois waterway involve removal efforts to maintain low abundance near the invasion front and surveillance to detect any spread farther upriver. However, the efficiency and effectiveness of these efforts may be limited by the low abundance and patchy distributions of bigheaded carps near the invasion front, as well as the spatial scope of the gears used to sample them. My thesis applied mobile hydroacoustic sampling to understand the factors influencing the distributions of silver carp near the invasion front in the upper Illinois waterway, and factors influencing the observability and detectability of fishes with this gear. These results will be useful to inform removal and surveillance efforts in the upper Illinois waterway and reduce the risk of further upstream invasion into the Great Lakes. To assess factors influencing abundance, bi-monthly (March - October) mobile hydroacoustic sampling was conducted from 2017-2018 and paired with continuous environmental variable data collection in the Dresden Island and Marseilles pools, the upper two invaded pools of the Illinois waterway. Environmental variables collected were water temperature, dissolved oxygen, total dissolved solids, turbidity, chlorophyll-a concentration, blue-green algae concentration, and depth. Logistic and multiple regressions were performed within pool during each sampling period to describe factors associated with silver carp presence, and factors associated with their densities in areas where they were present. Silver carp densities fluctuated across space and time, suggesting environmental variables influenced distributions. Depth was the most consistent predictor of silver carp presence and density, with shallower depths associated with higher abundance. Specifically, in summer months, areas in large backwater habitats with lower temperature, higher dissolved oxygen, and higher chlorophyll-a concentration tended to hold more silver carp. These results suggest removal efforts should be focused on shallower depths within sites, and should target areas in backwaters with lower water temperature, higher dissolved oxygen, and higher chlorophyll-a concentrations during summer months. To inform bigheaded carp surveillance efforts upstream of the invasion front, the influence of factors of vessel speed, wind speed, and beam compensation on the observability (the proportion of the true abundance of fish that fall within the acoustic beam) and detectability (the proportion of observable fish that are detected) of fishes in large rivers with mobile horizontal hydroacoustic sampling was also evaluated. To accomplish this, 23 sets of paired trawl floats (buoys) were deployed in a 2.1 km stretch of the Dresden Island Pool, and four sets of replicate hydroacoustic surveys were conducted past them at three vessel speeds. Mean wind speed during each survey was obtained, and proportion of buoys observed and detected were quantified under two different maximum beam compensation values (6 dB and 12 dB). Results revealed significant interactions between vessel speed and wind speed, with observability increasing with wind speed at slow and fast vessel speeds, but decreasing at intermediate vessel speeds. Detectability decreased with greater wind speed across all vessel speeds, with more pronounced effects at slower vessel speeds. Significant positive effects of beam compensation occurred for both observability and detectability. These results suggest, to improve detection of bigheaded carps, sampling should be focused on calm days under moderate vessel speeds when analyzing with standard beam compensation values. Broadening beam compensation was shown to increase observability and detectability, but needs further investigation. Ultimately, these studies provide valuable information to assist management efforts to control bigheaded carps near the invasion front in the upper Illinois waterway, and detect any individuals that may spread farther upriver towards the Great Lakes.