Smallmouth buffalo (Ictiobus bubalus Rafinesque) are a large-bodied fish highly valued and commercially exploited across most of their range. Despite this, relatively little is known of their population demographics compared to other exploited species. To fill these knowledge gaps, we analyzed two independent long-term datasets (30 and 57 years, respectively) and population demographic data (age structure, growth, mortality, age at maturity, and recruitment) from multiple pools of the Upper Mississippi River System (UMRS) and Illinois River (Illinois, USA). Long-term data (30-year dataset) generally show downward trends or significant declines in catch per unit effort in the UMRS, while the 57-year dataset shows a stable trend or a significant increase in the Illinois River. The oldest smallmouth buffalo were estimated to be 39 years old, with nearly every pool sampled having individuals estimated to exceed 30 years of age. Except for Pool 13 of the UMRS, 90

Rivers are increasingly used as superhighways for the continental-scale transportation of freight goods, but the ecological impact of large vessel traffic on river ecosystems is difficult to study. Recently, the temporary maintenance closure of lock and dam systems on the Illinois Waterway (USA) brought commercial vessel traffic to a halt along the river's length, offering a rare opportunity to study the response of the ecosystem before, during, and after an extended pause of this persistent anthropogenic disturbance. We observed improvements in main- and side-channel water quality and a redistribution of fish habitat-use during a months-long, near-complete reduction of large vessel traffic. Over 3600 water quality and 1300 fish community samples indicate that large vessel traffic reduction coincided with a 33 % reduction in turbidity as well as increased use of sampling strata near vessel navigation corridors by sound-sensitive and rheophilic fishes. Gizzard shad (Dorosoma cepedianum), the most abundant species in the system, also expanded their use of these 'impact' areas. Though inland waterway transport is an economically- and climate-friendly alternative to trucking and rail for the shipment of freight, our data suggest that intense vessel traffic may have profound physical and biological impacts across a large river. Monitoring and mitigation of ecological impacts of the ongoing expansion of inland waterway transport around the world will be critical to balancing large rivers as both useful navigation corridors and functional ecosystems.

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.

Despite an increasing interest in a recreational gar (family Lepisosteidae) fishery, little demographic information is available to inform sustainable management practices. Thus, our objectives are to (1) examine the relative abundance of Shortnose Gar Lepisosteus platostomus in the lower Illinois River 1993–2022, (2) estimate the current population structure and vital rates, and (3) estimate the population size through mark-recapture. Estimates of relative abundance were mostly stable or slightly increasing. The total length of Shortnose Gar ranged 30–771 mm and pectoral fin ray ages ranged 1–18 years, with most individuals captured in backwater habitats. Few individuals were recaptured suggesting the possibility of a large population size or a highly mobile population. The mean total length varied among gear types, but gear choice may not have a practical impact on size structure given the high overlap in total length ranges. Pectoral fin ray-derived vital rates suggest that Shortnose Gar in the Illinois River grow slower and have the potential to reach larger body sizes than previously described. Preliminary estimates of mortality rates suggest that fishing mortality remained low for this population as of 2018. The age structure and vital rate findings should be interpreted with caution as pectoral fin rays likely underestimate the age of Shortnose Gar but provide valuable baseline data for future comparisons. Future research should utilize otolith age estimates, determine exploitation levels, and assess movement ecology to better inform management strategies that provide for sustainable harvest of Shortnose Gar.

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.

This paper reports the first records of Cercopagis pengoi in the Mississippi River Basin, Illinois, USA.In 2017, a total of 11 C. pengoi were collected from two different locations during zooplankton sampling in the Illinois Waterway.One location was in the Chicago Sanitary and Ship Canal and the second location was in the Calumet-Sag Channel, approximately eight and 35 river kilometers from Lake Michigan, respectively.In 2021, eight additional individuals were encountered in ichthyoplankton samples collected in the Chicago Sanitary and Ship Canal, three river kilometers upstream of the 2017 capture location.The extent and density of C. pengoi within the Illinois Waterway is currently unknown; therefore, additional sampling is warranted to better understand their distribution and abundance to facilitate an assessment of the risks of spread to other connected waterways.

Large riverine systems are diverse and dynamic and are made up of multiple habitat types of lentic and lotic water. They are also heavily modified by humans and today nearly all habitats in many large rivers have been drastically altered. These modifications often include disconnecting lentic habitats either permanently or intermittently from the main channel. The Merwin Preserve at Spunky Bottoms (Merwin) began as a connected backwater that was leveed and drained for agriculture in the 1920s and restored in 1999, with restoration allowing it to become a disconnected backwater habitat. This status changed in 2013 when record flooding on the adjacent Illinois River overtopped and breached the levee creating an unmanaged and intermittent connection allowing the river access at moderately high river stages. During the past 20 years, the fish community at Merwin has undergone several changes that follow three drought events pre-breach, the exchange of fishes from the mainstem following the breach in 2013, and subsequent low water conditions of much of the area as river levels drop. Long term data and more intensive sampling efforts during the drought of 2012 showed relative abundance of sport fishes declined during, or immediately following, pre-breach drought events and post-breach low water conditions while relative abundance of non-sport and non-native fishes remained stable. The unique story of Merwin can provide a case study for other large river restoration projects on the effects of drought, climate change, and impacts of an unmanaged connection of a previously disconnected habitat to an adjacent large river.

The invasion of silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) or "bigheaded carps" has caused extensive ecological and economic harm throughout the Mississippi River and its tributaries. To prevent their continued spread upstream toward the Great Lakes, intense commercial harvest was implemented on the Illinois River, a large tributary that connects the Mississippi River to Lake Michigan. Since implementation, harvest has reduced densities at the invasion front while also presenting an opportunity to generate a synthesis on ecosystem resilience in the face of accelerating invasion. Resilience, the ability of an ecosystem to recover after perturbation, was observed at local scales and within some taxa but has yet to manifest at a river-wide scale and often co-varied with abiotic environmental or seasonal factors. Thus, while intensive harvest has limited further spread of bigheaded carps, and evidence of additional secondary ecosystem benefits exists, opportunities remain to identify potential pathways that could spread such ecosystem benefits even farther.

We examined the use of “edge of flood” habitats by larval silver carp during the extensive flooding that occurred in Pool 26 of the Upper Mississippi River near Alton, IL, USA and St. Louis, MO, USA during the summer of 2015. We captured over 12,700 individual fishes including eight taxa, over 12,000 of which (> 95%) were larval silver carp between 5 and 21 mm standard length. Peak catch rates occurred near the confluence of the Illinois and Mississippi rivers. These findings suggest that larval silver carp have an affinity for edge of the flood habitat and further study is needed to better understand how this affects the dynamics of this invasive species in the Mississippi River. The high catch rates observed at the confluence of the Illinois and Mississippi rivers suggests that the Illinois River is an important source of larval silver carp to the Upper Mississippi 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.

We tested the effectiveness of milfoil weevils (Euhrychiopsis lecontei) for reducing biomass of Eurasian watermilfoil (Myriophyllum spicatum, EWM) under natural lake conditions in a 3-year field experiment. In each of four lakes, we randomly chose two EWM beds for stocking and two beds as controls. A total of ca. 40,000 weevils were added to the eight stocked beds. During June and August 2013–2015, we measured plant diversity, biomass of EWM and native plants, and weevil abundance in the 16 study beds. Background weevil densities varied widely among beds and were often greater than the densities stocked. Weevil stocking had no significant effect on EWM or native plant biomass. Nevertheless, weevil damage to EWM was common and its extent appeared strongly related to observed densities of the weevil. ANCOVA results indicated that weevil density was a significant predictor of EWM biomass in both June and August, but not on growth during summer. Overall, our study found that weevil density is an important factor for predicting EWM biomass, while weevil density is likely affected by a large number of environmental factors. This work highlights the importance of carefully considering lake conditions that may influence the efficacy of stocking for biological control.