Use of non-lethal endpoints to establish water quality requirements and optima of the endangered Topeka shiner (Notropis topeka)

Water quality standards based on sub-lethal effects and performance optima for aquatic organisms, rather than onset of mortality, are more ecologically relevant for management of species of conservation concern. We investigated the effects of hypoxia, temperature (with acclimation), nitrogenous chemical compounds, and chloride on Topeka shiners (Notropis topeka) by monitoring behavioral responses to a reduction in oxygen and, using swimming speed, determining thermal optima and onset of effect for concentrations of nitrogenous compounds and chloride. We found ASR50 (i.e., dissolved oxygen concentrations where 50% of fish use aquatic surface respiration) to be 1.65 mg/L and ASR90 to be 1.08 mg/L of dissolved oxygen. Optimum temperatures for the species ranged from 17.7 to 28.0 °C, while predicted 100% mortality ranged from 33.7 to 40.3 °C, depending on the temperature at which fish were acclimated prior to experiments. Ammonia and sodium chloride reduced swimming speed at concentrations below known LC50 values, while nitrite concentrations did not correspond with swimming speed, but rather, post-experiment mortality. This provides insight into where Topeka shiners can not only persist, but also thrive. Although swimming speed may not be a suitable metric for determining the effects of all contaminants, our focus on optima and sub-lethal effects over tolerance allows selections of the most suitable reintroduction site matching the species’ physiological profile.

Comparison of Sampling Methods for Small Oxbow wetland Fish Communities

The value of wetland ecosystems is becoming increasingly recognized, promoting actions needed to preserve and restore them. Post-restoration monitoring is necessary to analyze restoration success or failure, thereby informing subsequent management decisions. Standardized monitoring protocols enable comparison of responses to restoration actions. Within the Midwestern United States, restoration of oxbow wetlands has become the focus of targeted restoration. Management objectives include recovery of biodiversity and sensitive species, and enhanced ecosystem services. The fish communities of oxbows have been the subject of many monitoring studies as endangered Topeka Shiner ( Notropis topeka ) use these habitats for spawning. However, an optimal method for monitoring Topeka Shiner and other fishes in oxbows has not been described, thereby limiting our capacity to effectively manage these ecosystems. With a primary objective of identifying a standardized protocol for sampling fish in oxbow wetlands, we compared efficacy of four sampling methodologies (backpack electrofishing, fyke netting, minnow trapping, and seining) for fish community data collection. Seining and fyke netting were determined to be the most effective methods for sampling oxbow fish communities. Although seining and fyke netting produced similar taxonomic diversity and abundance values, qualitative analysis revealed that seining caused greater habitat disturbance and stress to fish. Therefore, consideration must be given to how species present within the wetland could be impacted by sampling disturbance when choosing between seining and fyke netting.

Return of Topeka Shiner (Notropis topeka) to Restored Oxbows in the White Fox Creek Watershed, Iowa, USA

The Topeka shiner (Notropis topeka), a federally endangered species of minnow endemic to the Great Plains region of the central United States, has experienced widespread population declines resulting from loss of habitat. N. topeka habitat in Iowa, most notably oxbow wetlands, was mostly eliminated from the landscape during European settlement and agriculturalization of the region. Over the last two decades, restoration of oxbow habitats in Iowa has been increasing. Restorations provide critical habitat for N. topeka and regenerate a variety of ecosystem services that benefit many species of flora and fauna. There are signs that restoration of oxbow ecosystems is generating positive impacts on N. topeka recovery. Recent studies revealed that N. topeka populations are recovering within a few Iowa watersheds. In the investigation described here, we report the 2020 discovery of two N. topeka specimens in different restored oxbows within the White Fox Creek HUC10 of north central Iowa. Prior to these collections, the species had been undetected within this basin for 36 years. (It is possible that N. topeka persisted within the basin but remained undetected during sampling efforts.) Multiple oxbows have been restored within the White Fox Creek basin in recent years, and significant source populations of N. topeka can be found in nearby watersheds. These collections suggest that as oxbow restorations continue and land stewardship practices improve, N. topeka populations might recover and become reestablished within the historical range.

The Development of a GIS Methodology to Identify Oxbows and Former Stream Meanders from LiDAR-Derived Digital Elevation Models

Anthropogenic development of floodplains and alteration to natural hydrological regimes have resulted in extensive loss of off-channel habitat. Interest has grown in restoring these habitats as an effective conservation strategy for numerous aquatic species. This study developed a process to reproducibly identify areas of former stream meanders to assist future off-channel restoration site selections. Three watersheds in Iowa and Minnesota where off-channel restorations are currently being conducted to aid the conservation of the Topeka Shiner (Notropis topeka) were selected as the study area. Floodplain depressions were identified with LiDAR-derived digital elevation models, and their morphologic and topographic characteristics were described. Classification tree models were developed to distinguish relic streams and oxbows from other landscape features. All models demonstrated a strong ability to distinguish between target and non-target features with area under the receiver operator curve (AUC) values ≥ 0.82 and correct classification rates ≥ 0.88. Solidity, concavity, and mean height above channel metrics were among the first splits in all trees. To compensate for the noise associated with the final model designation, features were ranked by their conditional probability. The results of this study will provide conservation managers with an improved process to identify candidate restoration sites.

Use of non-lethal endpoints to establish water quality requirements and optima of the Topeka Shiner (notropis topeka)

Water quality influences growth, development, and physiology of aquatic vertebrates. Current criteria on water quality assessments are primarily based on lethal level experiments (e.g. LC50 tests), which are poorly suited for assessing optimal water quality conditions or sub-lethal effects of common stressors. Measurements below threshold values may still impede organismal growth and development, especially considering the complex nature of compounding, low-level stressors. This is particularly important to consider for management of an endangered species that is actively cultured for reintroduction to extirpated locations. The endangered Topeka Shiner (Notropis topeka) is an ideal example for which this information is needed, as its remaining, stable populations display broad water quality optima and tolerance to naturally occurring stressors. We investigated the effects of dissolved oxygen, temperature (including acclimation), ammonia, nitrite, and chloride on Topeka Shiner using non-lethal endpoints by: (1) examining N. topeka's behavioral responses to a gradual reduction in oxygen, (2) determining thermal optima at different acclimation temperatures using swimming speed, and (3) determining the onset of effect of sub-lethal levels of nitrogenous compounds and chloride concentrations on swimming speed. We determined ASR50 and ASR90 (i.e. dissolved oxygen concentrations where 50 percent and 90 percent of fish use aquatic surface respiration) to occur at 1.65mg/L and 1.08 mg/L of dissolved oxygen, respectively. At 5.52 mg/L of dissolved oxygen, fish vertical position was significantly higher in the water column, presumably in preparation or aquatic surface respiration (ASR). With our thermal swimming tests, the optimum temperature range was etermined to be 17.7 to 28.0 degrees C, while the predicted incipient mortality to high temperature ranged from 33.7 to 40.3 degrees C, depending on acclimation temperature. Ammonia and sodium chloride significantly reduced swimming speed at concentrations below known LC50 values. Other than an initial drop from 0- concentration, nitrite did not reduce swimming speed, even at concentrations higher than known LC50 measurements. Although not all stressors were suitable to test with this methodology, emphasis on determining optimal conditions over tolerances, and sub-lethal effects over mortality, assists in selection of sites that have water quality suited for N. topeka to thrive after reintroduction.