Zooplankton as an Indicator of the Ecosystem Response to Bigheaded Carp Suppression via Commercial Harvest in the Illinois River (2010 – 2017)

Current levels of Asian carp harvest lead to measurable increases in zooplankton abundance and biomass meaning zooplankton are an indicator of ecosystem response to carp suppression. However, diversity especially of large bodied cladocerans and copepods does not. This suggests that the most beneficial plankton food resources, cladocerans and copepods, are not recovering as quickly as the microzooplankton. Additionally, while there were differences in zooplankton community structure and population densities between years and among river reaches, these did not obscure the positive influence of harvest that zooplankton showed. What was known about Asian carp and plankton before this project: - The distribution of Asian carp has been expanding up the Illinois River towards Lake Michigan since at least the late 1990’s (Chick and Pegg 2001). - Where they establish and remain unmanaged, Asian carp densities have increased dramatically over time (DeBoer et al. 2018). - The upstream expansion of these carp appears to have stalled near Starved Rock Lock and Dam at roughly the same time as management actions (commercial fishing) were ramping up in the same area (Coulter et al. 2018). - Ambiguous response by primary production: chlorophyll is highly variable from year to year and depending on habitat (DeBoer et al. 2018) - Main channel zooplankton have declined and composition has shifted as carp have increased (Sass et al. 2014; DeBoer et al. 2018) - Native planktivorous fish body condition is strongly affected but the response of population size is more variable (Love et al. 2018; DeBoer et al. 2018; Pendleton et al. 2017) - Fish assemblage diversity and composition have both shifted measurably since 2000, but these responses have not been either quick or large (Solomon et al. 2017) What was not known about Asian carp and plankton before this project: Zooplankton are a basal food resource affecting all fish at some point in their life cycle. We have clear evidence that as the Asian carp presence increases the zooplankton abundance and biomass decrease leading to negative impacts on the ecosystem. However, as of 2018 we do not have clear evidence of whether suppression of the carp through commercial harvest mitigates those negative impacts on the plankton or planktivorous fish.Thus the goal of this project assesses whether zooplankton can tell us whether suppression of carp through commercial harvest is working and, ultimately, benefiting the ecosystem? More specifically; a) What is the lag time between management event/effort and a measurable response? b) Is there a harvest threshold to cross before there is a measurable response? What we can conclude because of this project: Section 1: Across the river the total species richness of all zooplankton has declined steadily as Asian carp have increased between 2010 and 2015. However, zooplankton density and biomass 3 which oscillated during the same period. Specifically, microzooplankton (Rotifers) dominated plankton numerically in all years, regions, and habitats. In contrast, macrozooplankton (Crustacean Copepods and Cladocerans) never dominate numerically, but are a disproportionately large part of the zooplankton biomass. In the upper river, where harvest pressure is strongest and carp abundance is lowest, interannual changes in zooplankton density and abundance are explained mainly by river hydrology (stage height and velocity) while biodiversity is explained mainly by water quality (temperature and turbidity). In contrast, temperature is the main factor affecting diversity, abundance, and biomass of zooplankton in the lower river where harvest is lower and carp abundance is higher. We believe the take-away message is that zooplankton community composition can be used as an indicator of ecosystem response to the arrival and expansion of invasive carp, if there is pre-existing info on what the plankton looks like without carp present in the river reach of concern. Section 2: Effect of standard single crew carp harvest by individual commercial fishing crews on is measurable and there is a relatively short lag time (i.e. weeks to months within the same summer). However, the response to harvest differs depending on type of zooplankton: microzooplankton (rotifers) responded to all tested levels of harvest but macrozooplankton (Cladocera, adult and juvenile Copepods) only responded to highest levels of removal (~10,000 kg per month). We believe a main take-away message should be that higher levels of harvest will lead to a greater benefit. Section 3: Effect of intense multi-crew harvest shows that greater harvest rate leads to greater positive ecosystem response. While the effect of harvest is significant, it can also complex and dependent on season and which category of zooplankton is considered (> 40,000 kg during a March 21 to April 1, 2016 event and an additional > 30,000 kg during a February 27 to March 10, 2017 event). Lag time to the initial positive response when the intense harvest took place in the early spring as in 2016 was as short as 4 to 5 weeks for rotifers and nauplii and 10+ weeks for Cladocera and Copepods. If the harvest event occurred late spring as in 2017, then the lag time decreased 3 – 4 weeks for rotifers, nauplii, Cladocera and Copepods. For instance, by day 89 of 2017 rotifers responded positively in both treatments suggesting seasonal succession was more important than harvest. However, by day 145 of 2017 rotifer density without harvest was lower than with harvest whereas the inverse was true for nauplii, and there was no difference for Cladocera and Copepods. We believe the take-away message is that while more intense harvest benefits the ecosystem, the level of benefit is dependent on the type of zooplankton as well as the season and year of harvest.Illinois Department of Natural Resources, Division of Fisheriesunpublishednot peer reviewedOpe

Status, trends, and population demographics of selected sportfish species in the La Grange Reach of the Illinois River

Abstract Sportfish species, specifically Yellow Bass Morone mississippiensis, White Bass Morone chrysops, Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, Black Crappie Pomoxis nigromaculatus, and White Crappie P. annularis, often drive economically valuable fisheries in large river systems, including the Upper Mississippi River System (UMRS).  Within the Illinois River, part of the UMRS, these species are routinely sampled by an ongoing long-term fisheries monitoring program.  Through this program, we investigated long-term trends (1993-2017) in catch rates and relative weights and quantified demographic rates from 2012-2016. We found all six species, with the exception of Yellow Bass, to have declining catch rates with this decline being most stark in larger, older fishes.  Population demographics for Yellow Bass, White Bass, Bluegill, and Black Crappie suggest populations are dominated by younger individuals, with only Black Crappie regularly living to age 3 and older, which may be driving population declines.  There are many environmental stressors acting on the Illinois River that could be contributing to the lack of older and larger fishes, including, but not limited to, navigation efforts, altered hydrology, pollution, sedimentation, lack of overwintering habitat, and introduction of invasive species.  Results of this study demonstrate that additional research to understand mechanisms driving reduced abundance and stunted age structure are needed to identify effective management actions that would benefit populations of recreationally valuable sportfish species

Status, trends, and population demographics of selected sportfish species in the La Grange Reach of the Illinois River

Sportfish species, specifically Yellow Bass Morone mississippiensis, White Bass Morone chrysops, Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, Black Crappie Pomoxis nigromaculatus, and White Crappie P. annularis, often drive economically valuable fisheries in large river systems, including the Upper Mississippi River System (UMRS). Within the Illinois River, part of the UMRS, these species are routinely sampled by an ongoing long-term fisheries monitoring program. Through this program, we investigated long-term trends (1993-2017) in catch rates and relative weights and quantified demographic rates from 2012-2016. We found all six species, with the exception of Yellow Bass, to have declining catch rates with this decline being most stark in larger, older fishes. Population demographics for Yellow Bass, White Bass, Bluegill, and Black Crappie suggest populations are dominated by younger individuals, with only Black Crappie regularly living to age 3 and older, which may be driving population declines. There are many environmental stressors acting on the Illinois River that could be contributing to the lack of older and larger fishes, including, but not limited to, navigation efforts, altered hydrology, pollution, sedimentation, lack of overwintering habitat, and introduction of invasive species. Results of this study demonstrate that additional research to understand mechanisms driving reduced abundance and stunted age structure are needed to identify effective management actions that would benefit populations of recreationally valuable sportfish species.is peer reviewedOpe

Status, trends, and population demographics of selected sportfish species in the La Grange Reach of the Illinois River

Abstract&#x0D; Sportfish species, specifically Yellow Bass Morone mississippiensis, White Bass Morone chrysops, Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, Black Crappie Pomoxis nigromaculatus, and White Crappie P. annularis, often drive economically valuable fisheries in large river systems, including the Upper Mississippi River System (UMRS).  Within the Illinois River, part of the UMRS, these species are routinely sampled by an ongoing long-term fisheries monitoring program.  Through this program, we investigated long-term trends (1993-2017) in catch rates and relative weights and quantified demographic rates from 2012-2016. We found all six species, with the exception of Yellow Bass, to have declining catch rates with this decline being most stark in larger, older fishes.  Population demographics for Yellow Bass, White Bass, Bluegill, and Black Crappie suggest populations are dominated by younger individuals, with only Black Crappie regularly living to age 3 and older, which may be driving population declines.  There are many environmental stressors acting on the Illinois River that could be contributing to the lack of older and larger fishes, including, but not limited to, navigation efforts, altered hydrology, pollution, sedimentation, lack of overwintering habitat, and introduction of invasive species.  Results of this study demonstrate that additional research to understand mechanisms driving reduced abundance and stunted age structure are needed to identify effective management actions that would benefit populations of recreationally valuable sportfish species.</jats:p

Threshold responses of freshwater fish community size spectra to invasive species

Abstract Aquatic invasive species (AIS) threaten biodiversity and ecosystem services around the world, but their management has been hampered by the lack of quantifiable control targets. The introduction of Silver Carp (Hypophthalmichthys molitrix) throughout the mid‐western United States epitomizes both the impacts of AIS and the need for quantitative control targets. Silver Carp are large‐bodied planktivores that compete with native planktivores, which can cause cascading effects throughout the food web. Our study tested the threshold of abundance beyond which Silver Carp alter fish assemblage structure. We used a community size spectra (CSS) approach to evaluate fish community size structure across temporal and spatial gradients of Silver Carp abundances. We hypothesized that Silver Carp would flatten the size spectra slope because they are large‐bodied and feed at a low trophic position. Electrofishing data were obtained for the La Grange Pool of the Illinois River (1994–2021) and for six pools of the Ohio River (2015–2020). Results supported our hypothesis, showing a 98% probability that the relative biomass of Silver Carp is positively related to the CSS slope (resulting in “flattening”). This pattern was strongest in the Illinois River, where Silver Carp made up >30% of fish assemblage biomass in recent years. The pattern was weakest in the Ohio River (78% probability of a positive relationship) where Silver Carp rarely exceeded 20% of total fish biomass. Subsequent changepoint models indicated that a Silver Carp relative biomass of ~24% represents a threshold below which negative food web impacts should be minimized. Our study demonstrates a clear shift in fish community size structure following invasion by Silver Carp and suggests that pre‐invasion CSS slopes may serve as a restoration target. It also illustrates the benefits of CSS to guide Silver Carp and other AIS management

Invasive Round goby <i>Neogobius melanostomus</i> distribution, relative abundance, and establishment in pools of the Illinois Waterway following 30 years of invasion

Round goby Neogobius melanostomus – a small, benthic fish native to Eurasia – was first introduced to North America in the 1980s through ballast water of cargo ships. In 1990, the Round goby was first discovered in the Laurentian Great Lakes Basin and rapidly spread through all Great Lakes from 1993 to 1998. The Round goby is an aggressive, prolific, and efficient egg predator that subsequently displaced native fishes from their preferred habitats and resources in the Great Lakes, where they are well established and abundant. From Lake Michigan, Round goby moved south into the Chicago Area Waterway System in 1993 and slowly progressed down the Illinois Waterway to the Mississippi River from 2004 to 2019, where less is known about their abundance, establishment, and impact. The goal of this study was to gain a comprehensive understanding of the first large river invasion by Round goby in the Mississippi River Basin by leveraging Round goby capture data from 2019 to 2022 on all pools of the Illinois Waterway. We describe their current distribution, relative abundance (i.e., catch-per-unit-effort), frequency of occurrence, and establishment (i.e., presence of young-of-year and adults) status throughout the Illinois Waterway. Results show that catch-per-unit-effort, frequency of occurrence, and the proportion of sites where multiple life stages are present are considerably higher in the upstream pools relative to more downstream pools of the Illinois Waterway. Our data support that the Round goby has established self-sustaining populations in the Chicago Area Waterway System, the upper Illinois River (i.e. Dresden Island Pool downstream through Starved Rock Pool), and a portion of the lower Illinois River (i.e. Peoria Pool downstream through Alton Pool) of the Illinois Waterway. In the lower Illinois River, Round gobies appear to only be established in Peoria Pool, with captures occurring infrequently in La Grange Pool, and no Round gobies being captured in Alton Pool.</p