While invasions of large rivers by exotic fish species are well documented, assessing actual or potential impacts on native species is a challenge. Rapid assessments may be possible through the application of a combination of bioenergetic and population dynamic models. Paddlefish (Polyodon spathula) is a native species in the central USA with a history of population decline due to waterway development and overharvesting for roe. It is not known whether paddlefish are impacted by resource competition from invasive bigheaded carp populations, including silver (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), which have expanded dramatically in the Mississippi River. We used bioenergetic models to project the potential impact of invasive silver and bighead carp on zooplankton density and paddlefish somatic growth in backwater habitat. Bioenergetic outputs were translated to impacts on fecundity, becoming inputs for 50‐year metapopulation simulations of backwater habitat connected to the main‐stem Mississippi River by episodic flood events. Competition with carp reduced growth and increased the risk of population decline for paddlefish. Impacts increased disproportionately with increased carp abundance and were further exacerbated in scenarios with increased diet overlap or decreased zooplankton abundance. We also analysed paddlefish condition data collected at sites near the lower Mississippi River with varying histories of carp invasion. These data give credence to the bioenergetic model output; paddlefish had reduced body condition at sites with long‐established, high‐density carp populations. We conclude that invasive bigheaded carps have great potential to reduce paddlefish growth, fecundity, and abundance. The pairing of bioenergetics and population models is likely to be broadly useful in assessing the risks posed by other invasive species.

The crayfish industry in Louisiana is the largest in the United States (McClain et al. 2007) with a value of more than $209 million (LSUAC 2012). The red swamp crawfish, Procambarus clarkii (Girard), and the southern white river crawfish, Procambarus zonangulus Hobbs and Hobbs, are harvested from managed ponds (farmed) and natural habitats (wild-caught) throughout Louisiana, with P. clarkii comprising the majority of landings. Farmed production of crayfish has increased over the past several decades and extensive research has examined P. clarkii responses to environmental parameters in these controlled aquaculture environments. In contrast, there has been limited research into the ecological influences on Louisiana P. clarkii populations from natural environments, which often exhibit episodic water level fluctuations and extensive variability in biotic and abiotic factors that can affect crayfish harvest and population structure.

Suckermouth catfi shes, native to Central and South America, have been established in US and Mexican waters since the 1950s (Fuller et al. 1999, Hill 2002) and have become problematic since the late 1990s (Hoover et al. 2004, Mendoza-Alfaro et al. 2009). Nuisance populations of these fi shes in three states (Hawaii, Texas, and Florida) have been implicated in a broad range of ecological problems, including erosion of streambanks and imperilment of threatened species, but documented accounts of their impacts are often equivocal and sometimes contradictory. This bulletin presents a conceptual model based on reports by the press and fi ndings by researchers working throughout the non-native range of these animals. The model is intended as a tool for identifying potential impacts of introduced suckermouth catfi shes on local fauna.

: Suckermouth catfishes, native to Central and South America, have been established in US and Mexican waters since the 1950s (Fuller et al. 1999, Hill 2002) and have become problematic since the late 1990s (Hoover et al. 2004, Mendoza-Alfaro et al. 2009). Nuisance populations of these fishes in three states (Hawaii, Texas, and Florida) have been implicated in a broad range of ecological problems, including erosion of streambanks and imperilment of threatened species, but documented accounts of their impacts are often equivocal and sometimes contradictory. This bulletin presents a conceptual model based on reports by the press and indings by researchers working throughout the non-native range of these animals. The model is intended as a tool for identifying potential impacts of introduced suckermouth catfishes on local fauna.

We targeted wadeable streams in six USEPA Level III ecoregions spanning eight major study basins in northern Gulf of Mexico coastal plains and terraces to identify appropriate spatial frameworks for the assessment of stream quality, as well as fish species and macroinvertebrate families that were characteristic of least disturbed conditions. We analyzed previously collected (1990-2006) and recently collected (2005-2010) stream fish and macroinvertebrate data with mean similarity analysis to identify spatial frameworks, either basins or ecoregions, appropriate for the assessment of stream fish and macroinvertebrates. We also conducted partial redundancy analysis of fish and macroinvertebrates separately, controlling for differences in stream size, and variance partitioning to identify the variation attributable to ecoregion or basin as a measure of the importance of spatial influence. Our results indicated that fish distributions were better described by basins, with anticipated strong dissimilarities in fish community composition between river basins west and east of the Mississippi River. In addition, we found unexpected differences in Pearl River and Red River basin fish communities relative to neighboring study basins and unexpected similarities among the geographically distant fish communities in the Western Gulf Coastal Plain and Mississippi Alluvial Plain Ecoregions. Conversely, once we accounted for the expected dissimilarity caused by the Mississippi River, macroinvertebrate data were better explained by ecoregion than basin. Our analyses indicated that the incorporation of both spatial classifications for assessment will be necessary in this region. Received September 8, 2011; accepted January 14, 2013

A specially designed net was used to study fish entrainment and injury through towboat propellers in 13 pools of the Upper Mississippi and Illinois rivers. The net was attached to the stern of a 48.8-m-long towboat with twin propellers (in Kort propulsion nozzles), and sampling typically took place while the towboat pushed 15 loaded barges upstream at a time. In total, 254 entrainment samples over 894 km of the 13 study pools were collected. The sampling efforts produced 16,005 fish representing 15 families and at least 44 species; fish ranged in total length from 3 to 123 cm, but only 12.5-cm or longer fish were analyzed because smaller fish could escape through the mesh of the trawl. Clupeidae (68% of total catch) and Sciaenidae (21%) were the dominant families. We detected no effects of towboat operation variables (speed and engine [i.e., propeller] revolutions per minute [RPM]) on entrainment rate (i.e., fish/km), but entrainment rate showed a wedge-shaped distribution relative to hydraulic and geomorphic characteristics of the channel. Entrainment rate was low (< 1 fish/km) in wide sections of the river, deep water, and swift current (or time periods characterized by faster flow); however, entrainment in narrow sections with shallow, slow water was highly variable and occasionally reached high levels (> 30 fish/km). Although total entrainment rate was not related to engine RPM, the probability of being struck by a propeller increased with fish length and engine RPM. Limits on engine RPM in narrow, shallow, and sluggish reaches could reduce entrainment impact, particularly for large-bodied fish.

Juvenile paddlefish Polyodon spat hula exhibit conspicuous variation in the shape of their rostra and caudal fins. We quantified morphological variation for a composite collection of young-of-year paddlefish (N = 55; 61.9-403.7 mm total length) using nine measurements of the rostrum, body, and caudal fin. Sheared principal component analysis of morphological data resulted in three distinct groups of fish corresponding to three different localities: hatchery-reared fish from the Mermentau River, Louisiana; hatchery-reared fish from the Tombigbee River, Alabama; and field-collected fish from the Mississippi River, Mississippi. Series were segregated from each other based on size of caudal lobes and width of rostrum. With increased body size of fish, relative length of rostrum increased, and mesal expansion of rostrum increased for all three series. For Tombigbee and Mississippi River series, with increased size of fish, caudal asymmetry decreased. Overall, smaller fish had shorter, narrower rostra and highly asymmetrical caudal lobes; larger fish had longer, broader rostra and more symmetrical caudal lobes. Morphological differences among series were most conspicuous for fish greater than 85 mm eye-to-fork length. Fish from Mermentau River had shorter, narrower (leaf-shaped) rostra and asymmetrical (conspicuously heterocercal) caudal lobes. Those from the Tombigbee River had longer, broader (spoon-shaped) rostra and more symmetrical caudal lobes. Those from the Mississippi River had the longest, broadest (paddle-shaped) rostra and symmetrical (superficially "homocercal") caudal lobes. Locality-based gradient in paddlefish morphology corresponds to a gradient in river hydrology: longer, broader rostra and symmetrical caudal lobes were associated with larger basins, higher gradients, and greater discharge.

Abstract : Habitat models are used to evaluate impacts of water resource development activities such as flood control and navigation projects, and environmental benefits of restoration or mitigation projects. These models generally take the form of an index ranging from 0.0 (poor habitat) to 1.0 (optimum habitat), referred to as a Habitat Suitability Index (HSI). HSI's are used to weight acres of affected habitat, a method compatible with the commonly used Habitat Evaluation Procedure (www.fws.gov/policy/hbindex.cfm) or Instream Flow Incremental Methodology (www.fort.usgs.gov/Products/Software/IFIM/). Both of these methods multiply quality (i.e., HSI) and quantity (e.g., acres) to determine habitat conditions. HSI s represent the biological components of the evaluation (e.g., number of species, relative abundance) and their responses to changes in habitat conditions. The multiplicative product of HSI and acres of habitat is a unit (e.g., Habitat Unit, Weighted Usable Area) that can be compared among project alternatives and averaged over the life of the project (e.g., Average Annual Habitat Unit). The U.S. Army Engineer Research and Development Center (ERDC) continues to evaluate consequences of flood control, water supply, and navigation projects on fish assemblages, as well as benefits of aquatic restoration. Many of these projects have been completed through leveraged funds from Corps of Engineers Districts (primarily Vicksburg and Memphis Districts) and the Ecosystem Management and Restoration Research Program at ERDC. HSI models are based on field-derived correlations between biotic-abiotic variables, resulting in a library of regression equations developed over the past 10 years. The purpose of this technical note is to summarize the HSI models and describe their development and applicability as assessment tools in similar aquatic systems.

BACKGROUND AND PURPOSE: Delta streams, forming in the floodplains of large river systems, are widespread throughout the United States. Delta streams are most prevalent in the Mississippi Embayment, also referred to as the lower Mississippi River Basin. The alluvial flood- plain deposits are typically rich in organic material. Consequently, most delta streams have been altered through intense agricultural activities and flood control measures. Low water, excessive sedi- mentation in smaller delta streams, and the accumulation of pesticides such as DDT are the consequences of these anthropogenic disturbances resulting in dominance of tolerant fish species. Characteristics of tolerant fish assemblages include adaptations to low dissolved oxygen and high pulses of suspended solids, no direct requirements for clean, firm substrates for spawning, and ability to live in shallow, slackwater pools for extended periods. Although degraded delta streams are prevalent in the United States, attempts have been made to restore habitat conditions as part of ecosystem restoration or mitigation of flood control projects. One such project occurred in the Upper Steele Bayou System (USBS) in west central Mississippi. The USBS encompasses 282 square miles in the Yazoo Delta of the lower Mississippi River basin. All of the streams in the USBS lie within a predominately agricultural landscape and were highly degraded from low water and sedimentation. Fishes were sampled in 1990, and again in 1994, to establish baseline conditions and evaluate potential impacts and mitigation requirements of a pro- posed flood control project (Killgore and Hoover 1991). However, restoration measures were also incorporated into the plan. Between 1995 and 2001, seven weirs were constructed; 66 drop pipes were placed in surrounding agricultural lands next to the streambank to reduce erosion; and approxi- mately 63 miles of channel enlargement, cleanout, and selective snagging were completed that removed soft, unconsolidated substrates and improved flow conveyance (Figure 1). These were recognized as watershed-level benefits to aquatic communities. Consequently, habitat and fishes of the USBS were re-sampled repeatedly from 2000 to 2005 to document the current status of the fish assemblage and compare these data to collections made in the early 1990s. On September 24, 2005, Hurricane Rita caused major flooding in the Yazoo Delta during a period of low water conditions. Water levels were elevated with a concomitant increase in biological oxygen demand caused by influx of organic debris, which resulted in widespread hypoxia throughout the delta. Fish kills were reported, low

: This study summarizes recent observations of silver carp, Hypopthalmichthys molitrix, in small wetlands of the Lower Mississippi River and suggests management actions for their control based on wetland hydrology and pattern of fish movements.

Abstract : Delta streams, forming in the floodplains of large river systems, are widespread throughout the United States. Delta streams are most prevalent in the Mississippi Embayment, also referred to as the lower Mississippi River Basin. The alluvial flood-plain deposits are typically rich in organic material. Consequently, most delta streams have been altered through intense agricultural activities and flood control measures. Low water, excessive sedimentation in smaller delta streams, and the accumulation of pesticides such as DDT are the consequences of these anthropogenic disturbances resulting in dominance of tolerant fish species. Characteristics of tolerant fish assemblages include adaptations to low dissolved oxygen and high pulses of suspended solids, no direct requirements for clean, firm substrates for spawning, and ability to live in shallow, slackwater pools for extended periods. Although degraded delta streams are prevalent in the United States, attempts have been made to restore habitat conditions as part of ecosystem restoration or mitigation of flood control projects.

The Fort Worth District Corps of Engineers and the San Antonio River Authority (SARA) are formulating and evaluating plans for habitat restoration of the San Antonio River. Four alternatives (Design Conditions 1-3B) are being considered that include re-establishment of forested riparian zone, creation of meanders, channel excavation, and increasing complexity of substrate and flow patterns. Field data of fish and aquatic habitat were collected and used to determine baseline conditions and develop habitat models to predict benefits of restoration alternatives. Thirty-two species of fish were collected and the community was dominated taxonomically by minnows, sunfishes, cichlids and livebearers . Thirteen of the fish are not indigenous to the system. Biomass was dominated by suckermouth catfishes. Degraded habitat conditions prevailed in the study area primarily due to the lack of slackwater and instream/riparian strucuture except for large rubble. HEP analyses demonstrate that all four Design Conditions will result in substantial gains in HUs. Total HUs was greatest for DC3B. Smaller erosional sediments and littoral vegetation will increase enhancing spawning and rearing of most native fishes. Leaves, small woody debris, and detritus will be transported into the channel by wind from adjacent riparian zones. Overall, the restoration project will contribute to a sustainable ecosystem by providing physical habitat complexity and stability, food resources to invertebrates and fishes, and nursery resources to fishes.