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Within the Great Plains region of North America, oxbow wetlands were lost as streams were channelized and straightened to allow for agricultural use of the landscape. Topeka Shiner, which rely on these oxbow wetlands, have declined in abundance, currently occupy 20% of their historical geographic range, and are now an endangered species. A large emphasis has been placed on restoring oxbow wetlands to recover Topeka Shiner populations. As the number of oxbow restorations has increased, so has the number of monitoring projects focused on these habitats. Currently, conservation practitioners rely on the presence of Topeka Shiner to determine the success of an oxbow restoration. Given the rarity of the species, this method is likely ineffective. Within this study we attempt to create a model that can be used to determine the success of an oxbow restoration that will benefit the Topeka Shiner without relying on the presence of the species in the wetland. We used multiple fish community metrics and modelling strategies to determine the best model for predicting Topeka Shiner CPUE and presence/absence within oxbows. We determined that the top models were ineffective at predicting Topeka Shiner CPUE and presence/absence. Our findings illustrate the random nature by which fish communities become established within oxbows, and the island-like nature of oxbows in terms of how fish communities may become established and change over time. These findings indicate that the success of oxbow restoration for Topeka Shiner needs to be defined at a larger scale than for individual oxbows. Furthermore, our findings corroborate the inability of previous studies to determine reproducible associations of Topeka Shiner with various fish community metrics., INTRODUCTION Human land use and resulting declines in aquatic ecosystem habitat abundance and quality have led to declines in freshwater fish abundance and species diversity (Jelks el al., 2008; Gido, [...]

Three species of invasive carp—Grass Carp Ctenopharyngodon idella, Silver Carp Hypophthalmichthys molitrix, and Bighead Carp H. nobilis—are rapidly spreading throughout North America. Monitoring their reproduction can help to determine establishment in new areas but is difficult due to challenges associated with identifying fish eggs. Recently, random forest models provided accurate identification of eggs based on morphological traits, but the models have not been validated using independent data. Our objective was to evaluate the predictive performance of egg identification models developed by Camacho et al. (2019) for classifying invasive carp eggs by using an independent data set. When invasive carp were grouped as one category, predictive accuracy was high at the following levels: family (89%), genus (90%), species (91%), and species with reduced predictor variables (94%). Invasive carp predictive accuracy decreased when we only considered observations from newly sampled locations (family: 9%; genus: 22%; species: 30%; species with reduced predictor variables: 70%), suggesting potential differences in egg characteristics among locations. Random forest models using a combination of previous and new data resulted in high predictive accuracy for invasive carp (96–98%) when invasive carp were grouped as one class for all models at the family, genus, and species levels. The two most influential predictor variables were average membrane diameter and average embryo diameter; the probability of predicting an invasive carp egg increased with these metrics. High predictive accuracy metrics suggest that these trained and validated random forest models can be used to identify invasive carp eggs based on morphometric variables. However, decreased performance at new locations suggests that more research would be beneficial to determine the models' applicability to a larger spatial region. [ABSTRACT FROM AUTHOR]

Invasive carp are expanding throughout the upper Mississippi River basin and are of great concern due to their potential economic and ecological impacts. Identification of spawning locations provides critical information on recruitment sources to evaluate potential management strategies. Our objective was to create and validate a spawning habitat suitability model of the Des Moines River, Iowa, during low‐, average‐, and high‐water‐level conditions. Backwater availability, abundance of hardpoints (structures that create turbulence), river gradient and sinuosity, water temperature, and continuously free‐flowing river lengths were used as model parameters. The model was compared to back‐calculated spawning locations from invasive carp eggs collected in 2014–2015. Turbulent hardpoints, river sinuosity, and gradient were not significant predictors of invasive carp spawning locations, and backwater availability in the 25 river kilometers downstream of each reach was inversely correlated with invasive carp spawning locations. Invasive carp eggs were not caught in 2014 despite optimal spawning conditions, revealing that spawning may have high interannual variation. This study suggests that predicting invasive carp reproduction may require variables in addition to those currently proposed. [ABSTRACT FROM AUTHOR]

Continuous harvest over an annual period is a common assumption of continuous biomass dynamics models (CBDMs); however, fish are frequently harvested in a discrete manner. We developed semidiscrete biomass dynamics models (SDBDMs) that allow discrete harvest events and evaluated differences between CBDMs and SDBDMs using an equilibrium yield analysis with varying levels of fishing mortality (F). Equilibrium fishery yields for CBDMs and SDBDMS were similar at low fishing mortalities and diverged as F approached and exceeded maximum sustained yield ([F.sub.MSY]). Discrete harvest resulted in lower equilibrium yields at high levels of F relative to continuous harvest. The effect of applying harvest continuously when it was in fact discrete was evaluated by fitting CBDMs and SDBDMs to time series data generated from a hypothetical fish stock undergoing discrete harvest and evaluating parameter estimates bias. Violating the assumption of continuous harvest resulted in biased parameter estimates for CBDM while SDBDM parameter estimates were unbiased. Biased parameter estimates resulted in biased biological reference points derived from CBDMs. Semidiscrete BDMs outperformed continuous BDMs and should be used when harvest is discrete, when the time and magnitude of harvest are known, and when F is greater than [F.sub.MSY]. Si les modeles continus de dynamique de la biomasse (CBDM) partent souvent du principe que la capture est continue au cours d'une periode annuelle, les prises de poissons s'effectuent frequemment de maniere discrete. Nous avons mis au point des modeles semidiscrets de dynamique de la biomasse (SDBDM) qui permettent l'integration d'evenements de prise discrets et avons evalue les differences entre les CBDM et les SDBDM a la lumiere d'une analyse du rendement equilibre a differents taux de mortalite par peche (F). A de faibles F, les CBDM et les SDBDM ont donne des rendements equilibres semblables, l'ecart entre ces derniers augmentant a mesure que F s'approche puis depasse le rendement maximum durable ([F.sub.MSY]). L'integration de prises discretes s'est traduite par des rendements equilibres plus faibles a des F eleves que ceux obtenus pour des prises continues. L'incidence de l'utilisation de prises continues dans des cas ou les prises sont en fait discretes a ete evaluee en ajustant les CBDM et les SDBDM aux donnees de series chronologiques generees pour un stock hypothetique de poissons faisant l'objet de prises discretes et en evaluant le biais des estimations de parametre. L'integration de prises discretes a fait en sorte que les CBDM ont donne des estimations de parametre biaisees alors que les estimations de parametre decoulant de SDBDM n'etaient pas biaisees. Les estimations de parametre biaisees se sont traduites par des points de reference biologiques biaises decoulant des CBDM. Les SDBDM ont donne de meilleurs resultats que les CBDM et devraient etre utilises dans les cas ou la capture est discrete, ou le moment et la magnitude des prises sont connus et ou F est superieur a [F.sub.MSY]. [Traduit par la Redaction], Introduction Biomass dynamics models (BDMs) are the simplest stock assessment models used to manage fish stocks when stock data are limited to biomass harvested and biomass estimates or indices. Compared [...]

Understanding spatial variation in non‐native fish species population ecology is imperative, where environmental, biotic and invasion‐related mechanisms contribute to spatial heterogeneity. Established populations of invasive silver carp Hypophthalmichthys molitrix are currently found throughout a large portion of the upper Mississippi River (UMR) basin. Despite their recent invasion and broad environmental tolerances, silver carp population ecology and linkages to environmental conditions in the UMR remain understudied. There were two objectives for this investigation: (a) to estimate correlations among population characteristics and the influence of latitude and the time since first detection, and (b) to model the influence of river discharge and temperature on growth early in life to age 3. We estimated spatial variability in silver carp population characteristics and dynamics from nine sites across the UMR and assessed if biotic, abiotic or invasion‐related (time since first detection) variables influence spatial patterns. Silver carp body weight, size structure, annual mortality, and growth parameters varied among locations. Silver carp recruitment was less stable for populations with higher relative abundance estimates and where carp were first detected ≥20 years ago whereas maximum carp age decreased with increasing latitude. Although model selection indicated silver carp length at age 3 was associated with mean daily discharge (m3/s) coefficient of variation, mean May‐June temperatures, and ordinal date of maximum discharge, parameter coefficients and effect sizes were small and not biologically meaningful. Our results suggest that silver carp populations are governed by intraspecific mechanisms, but time‐dependent changes in populations may partially underpin heterogeneity across populations. Our study helped further disentangle silver carp population ecology in the UMR by understanding carp ecology as a function of their invasion. [ABSTRACT FROM AUTHOR]

Despite the longstanding presence of grass carp Ctenopharyngodon idella in the Upper Mississippi River (UMR) watershed, information regarding their populations remains largely unknown, in part because capture is difficult. Occupancy models are a popular wildlife assessment tool to account for imperfect detections but have been slow to be adopted in fisheries. Herein, we used occupancy modelling to evaluate the influence of two environmental covariates (river discharge and water temperature) on grass carp occupancy, extinction, colonization, and detection at nine sites within south‐eastern Iowa rivers from April to October 2014 and 2015. Grass carp were detected at least once at all but one site. The most parsimonious model indicated that grass carp colonization probability increased from 0.15 to 0.67 with increases in river discharge. In contrast, occupancy (0.20), extinction (0.29), and detection (0.50) probabilities were temporally constant. Models indicated that water temperatures did not influence grass carp extinction or colonization probabilities relative to river discharge. Cumulative grass carp detection probability approached 1.0, whereas conditional occupancy estimates were less than 0.1 when using five or more sampling transects. The use of a robust design occupancy model allowed us to estimate site occupancy rates of grass carp corrected for imperfect detections, while demonstrating the importance of river discharge for site colonization. These results can be used to assess the distribution of a cryptic fish while helping to guide grass carp sampling and removal efforts. [ABSTRACT FROM AUTHOR]