Diets of Invasive Channel Catfish are Subsidized by Invasive Riparian Trees

Russian olive (Elaeagnus angustifolia) is an invasive, fruit- bearing riparian tree that dominates riparian zones of the San Juan River in the southwestern United States. Previous research in this river suggests olive fruit is common in diets of invasive channel catfish (Ictalurus punctatus), but its energetic importance is unknown (i.e. critical for catfish fitness vs. incidental consumption). We assessed Russian olive consumption in channel catfish diets bimonthly for 1 year, hypothesizing that olive consumption would be greatest during periods of high olive availability and low benthic aquatic invertebrate availability. We found that catfish consumed olive fruit throughout the year and that olive comprised up to 44% of total stomach contents by mass, with peaks in spring and fall. Regression models revealed the presence and mass of olive fruit in catfish stomachs were positively associated with catfish total length, with a significant interaction between water temperature and river discharge. Catfish were more likely to consume olive fruit during higher flows, regardless of temperature and at low discharge with higher temperature. Contrary to our hypothesis, neither olive nor benthic invertebrate availability were associated with olive presence in channel catfish diets. Nutrition analysis indicated that olive alone was a low-quality diet item but has the potential to provide a reliable energy source. We used seasonal data to estimate the energetic contribution of olive fruit to catfish populations using a bioen-ergetic model, which estimated that olive fruit accounted for 35.6% of energy (Joules) consumed by catfish populations and satisfied 38% of their metabolic demand. Our results suggest that Russian olive fruit is a significant subsidy to channel catfish in the San Juan River. However, more research is needed to determine the indirect effects of this interaction on native fishes and ecosystem function

Consistency of Mobile and Sedentary Movement Extremes Exhibited by an Invasive Fish, Silver Carp \u3cem\u3eHypophthalmichthys molitrix\u3c/em\u3e

Within many populations, some individuals may be more apt to move, and these individuals can substantially impact population dynamics. Invasive Silver Carp (Hypophthalmichthys molitrix) have spread throughout much of the Mississippi River Basin, and their presence has resulted in multiple negative ecosystem effects. Silver Carp are known to move hundreds of km, which has likely contributed to their rapid spread. Our study examined movement patterns and environmental cues for movement in Silver Carp based on acoustic telemetry of tagged fish that ranged widely (i.e., mobile) and those that did not range far from the site of their original capture and tagging (i.e., sedentary) in the Wabash River, USA. Sedentary and mobile designations were made based on observed extremes of mean annual ranges, and these designations were consistent within seasons and among years. Both movement groups displayed seasonal variation in movements, with mobile Silver Carp consistently moving greater distances within each season and sedentary Silver Carp exhibiting lower variability in distances moved than mobile individuals. Discharge (change in discharge) and temperature were significant predictors of mobile and sedentary individuals’ movements. Additional environmental variables (i.e., cumulative growing degree day, day of year, and change in temperature) also related to movement likelihood of sedentary individuals, whereas total length was the only additional variable that influenced movement likelihood of mobile individuals. Total length was significantly related to movement distance for both groups of Silver Carp, but the relationship was negative for sedentary fish and positive for mobile fish. Results point to differences in behavior that may require targeted management strategies to achieve agency goals to interrupt mobile individual movements that can result in range expansion. Such strategies may also limit introductions and invasions by other aquatic invasive species that exhibit similar behaviors

Short-term exposure to elevated suspended sediment increases oxygen uptake of gilled larval Eastern Hellbender salamanders (Cryptobranchus alleganiensis)

Freshwater ecosystems are increasingly impacted by anthropogenic elevated levels of suspended sediment that may negatively affect aquatic organisms, including salamanders. While increasing fine sediment in streams has been suggested as a reason for population declines, to date no study has empirically assessed the effect of suspended sediment on gilled larval Eastern Hellbenders (Cryptobranchus alleganiensis Daudin, 1803), a critical life history stage and species of conservation concern. We used custom respirometers to elucidate effects of suspended sediments on larval Hellbender oxygen uptake in trials conducted in situ in Georgia streams. Mean oxygen uptake increased and was significantly higher in trials when larval salamanders were exposed to suspended sediment (mean = 5.06 O2 mg/L, 800 mg/L sediment treatment vs 2.25 O2 mg/L, 0.00 mg/L sediment control). This may indicate elevated physiological stress in response to short term exposure to suspended sediments. Qualitatively, individuals in both groups exhibited rocking behavior in response to low oxygen (hypoxia), albeit at different frequencies (sediment exposure = 7.6 rocks per minute and control = 2.1 rocks per minute). Larval salamanders may be able to temporarily compensate for low oxygen through increased rocking behavior when high suspended sediment loads are present, with future respirometry research needed.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Assessing Impacts of Land-Applied Manure from Concentrated Animal Feeding Operations on Fish Populations and Communities

Concentrated animal feeding operation (CAFO) manure is a cost-effective fertilizer. In the Midwest, networks of subsurface tile-drains expedite transport of animal hormones and nutrients from land-applied CAFO manure to adjacent waterways. The objective of this study was to evaluate impacts of land-applied CAFO manure on fish populations and communities. Water chemistry including hormone, pesticide, and nutrient concentrations was characterized from study sites along with fish assemblage structure, growth, and endocrine disruption assessed in selected fish species. Although most CAFO water samples had hormone concentrations <1 ng/L, equivalent concentrations for 17β-E2 and 17α-TB peaked at >30 ng/L each during the period of spawning, hatching, and development for resident fishes. CAFO sites had lower fish species richness, and fishes exhibited faster somatic growth and lower reproductive condition compared to individuals from the reference site. Fathead minnows (<i>Pimephales promelas</i>) exposed to CAFO ditchwater during early developmental stages exhibited significantly skewed sex ratios toward males. Maximum observed hormone concentrations were well above the lowest observable effect concentrations for these hormones; however, complexities at the field scale make it difficult to directly relate hormone concentration and impacts on fish. Complicating factors include the consistent presence of pesticides and nutrients, and the difference in temperature and stream architecture of the CAFO-impacted ditches compared to the reference site (e.g., channelization, bottom substrate, shallow pools, and riparian cover)