Paddlefish Polyodon spathula and three sturgeon species are present in the upper Mississippi River; of these four species, two are commercially and recreationally important (Paddlefish and Shovelnose Sturgeon Scaphirhynchus platorynchus), and two are protected under federal or state endangered species laws (Pallid Sturgeon S. albus and Lake Sturgeon Acipenser fulvescens). Before management strategies can be implemented, quantification of movement patterns is necessary to determine the appropriate spatial scale for management. To increase the available relevant information, we investigated broad-scale movement patterns of the above species in the upper Mississippi River by using telemetry. All four species were capable of long-range (>300-km) movements, and these movements were cued by the changing river stages and water temperature. Ultimately, our data suggest that sturgeon and Paddlefish movement patterns are highly variable, with fish moving freely among rivers (e.g., the Mississippi, Missouri, Illinois, Ohio, and Des Moines rivers) across many political boundaries and encompassing multiple regulatory agencies. This migratory nature can lead to portions of the population being subject to harvest in multiple management units, affecting population dynamics, biology, harvest, and management/recovery in both the natal area and in the harvest areas. To effectively manage or recover these highly mobile fish populations, interjurisdictional collaboration will be necessary.

The diet composition was quantified of year-0 Scaphirhynchus sturgeons during sampling years (2004-2008) from the Middle Mississippi River to evaluate trends in diet. River stage height varied among years and seasons. Water temperature differed among seasons but did not differ among years. The presence of empty stomachs was evident across years, seasons, and size classes of sturgeon. The overall Multivariate Analysis of Variance for frequency of occurrence was significant, suggesting that macroinvertebrate taxa (e.g. Ephemeroptera, Diptera pupae, Chironomidae, Other) differed among size classes of sturgeon, but not seasons or years. Furthermore, Tukey's pairwise comparisons indicated Ephemeroptera frequency of occurrence differed between medium and large size classes; Diptera pupae differed between small and medium size classes and small and large size classes; Chironomidae differed between small and large size classes and medium and large size classes; the macroinvertebrate taxa category Other differed between small and large size classes. Ultimately, because of the link between diet and growth of year-0 Scaphirhynchus sturgeon, the early life history may affect eventual recruitment to adult stages.

Length measurements of fishes are commonly used by fishery scientists because of their ease of collection and the profound insight into fish populations that they provide. Specifically, obtaining accurate fish lengths is imperative for obtaining accurate population demographics. Thus, reproducibility and consistency of measuring an individual fish over time can greatly influence population level metrics and ultimately management decisions. To investigate this, we recorded fork lengths of 526 shovelnose sturgeon Scaphirhynchus platorynchus captured, measured, and marked in the field and recaptured within six years. Secondarily, we evaluated 37 shovelnose sturgeon measured in a controlled laboratory setting. We found that in both our field and laboratory evaluation that experienced biologists (between 5 and 20 years experience as fishery biologists) inaccurately measured (greater than 15mm reduction in length) shovelnose sturgeon in approximately 5% of all cases. Of the approximately 5% erroneous measurements, substantial negative growth (greater than 100mm reduction in length) occurred in some situations. This suggests that errors in recorded fish lengths exist and because of this, we believe multiple steps should be taken to minimize measurement error. Individual fishery biologists performing measurements should strive to ensure every fish is measured properly (i.e., fish laid completely flat on measuring board) and is recorded accurately. To this end, fishery biologists must accept that measurement error occurs and perform periodic quality assurance/quality control measures to account for these inaccuracies.

The main stems of large rivers throughout the world have been highly modified with little consideration for effects on fishes that rely on these areas to complete their life histories. Particularly important is the ability of riverine habitats to provide foraging opportunities for young fish. We explored how temperature, flow, and food availability influenced diet content, prey selection (Strauss's linear selectivity index), and energy condition of age-0 shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus in major habitat areas (e.g., islands, channel borders, wing dikes, and side channels) of the middle Mississippi River during spring (March-May) and summer (June-August) 2008. Standardized diet mass (dry mass standardized for fish body mass) of the age-0 sturgeon peaked at about 19 degrees C and at a flow velocity of 0.5 m/s. Although potential prey taxa were diverse, the diets for age-0 sturgeon of all sizes were dominated by mayflies (Ephemeroptera) and midge larvae (Chironomidae) across all habitats. As age-0 sturgeon grew, the relative energy return per habitat appeared to diverge; island tips upstream of the main channel and channel border areas behind wing dikes provided higher gains in standardized diet mass than other habitats. No differences in energy condition (kJ/g) occurred among habitats, although large (51-200 mm total length [TL]) age-0 sturgeon had higher energy densities than their small (<= 50 mm TL) counterparts. Enhancement of areas with flow and substrates that facilitate the production and availability of midges and mayflies (e.g., instream island complexes) is critical for the recruitment of age-0 Scaphirhynchus sturgeon in large rivers.

Understanding linkages between natal and nursery habitats is critical for conservation of riverine fishes. Scaphirhynchus sturgeons inhabiting the middle Mississippi River may originate from the Missouri or Mississippi rivers, although relative importance of these recruitment sources is unknown. We characterized the relationship between water and sturgeon fin ray Sr:Ca, verified shifts in water Sr:Ca are recorded in age-0 sturgeon fin rays, and determined whether age-0 sturgeons from the Mississippi and Missouri rivers exhibited distinct fin ray Sr:Ca signatures. Fin ray Sr:Ca of laboratory-reared fish reflected transfer from water with elevated Sr:Ca to ambient water 1 day posthatch, indicating that short-term residency in environments can be detected. Nine of 30 age-0 fish captured in the middle Mississippi River were Missouri River emigrants. Four of these emigrants originated in the upper portion of the lower Missouri River (≥589 km upstream from its mouth), where water Sr:Ca is higher compared with the lowermost section of the Missouri River and the Mississippi River. Twenty-five of 30 fish collected from the lowermost section of the Missouri River originated within this river segment; the remainder originated upriver. Fin ray Sr:Ca enables identification of natal river segment for age-0 sturgeons and contributions of river segments to sturgeon recruitment.

Blue catfish Ictalurus furcatus are a commercially and recreationally important species throughout their range, in which many states have differing management strategies. Before management strategies can be implemented to achieve specific goals, understanding seasonal habitat use and movement patterns is necessary to determine the appropriate spatial scale for management. Therefore, we determined the extent and timing of blue catfish movement in the upper Mississippi River (UMR). During fall 2006 through spring 2010, 92 blue catfish (ranging from 490 to 1,025 mm total length) were captured, implanted with ultrasonic transmitters, and released in the Lock and Dam 26 area. Movement was quantified in the UMR from below Lock and Dam 19 down to the Ohio River confluence, including major tributaries, by examining the average (kilometers moved between detections/number of detections) and maximum (total number of kilometers moved across all detections) movements for each fish throughout the life of each transmitter that was detected multiple times by the stationary receiver array. Of the 82% of fish detected by stationary receivers, movement occurred from Mississippi River kilometer 459 to the Ohio River confluence, with individual blue catfish movement ranging from a maximum of 689 river kilometers to a minimum of 1.3 river kilometers. Fifteen (19%) of the fish tagged in the UMR moved into one or more of major tributaries (the Missouri, Illinois, Meramec, and Ohio rivers) while 31 (41%) of the fish stayed in the Alton area year-round and 30 (40%) blue catfish moved down into the open river to possibly overwinter. When investigating total movement by tagged blue catfish each month, the greatest movement occurred during periods of changing water temperatures and high discharge. This was further supported by the Akaike's information criterion, with the interactive model of temperature and discharge resulting in the most support for triggering blue catfish movement. Understanding these movement patterns and seasonal habitat requirements for spawning, foraging, or refuge of riverine fish is essential for effective management of these highly mobile fish.

Channel catfish Ictalurus punctatus are a major recreational and commercially important large river species. However, anthropogenic activities have heavily degraded the majority of riverine catfish habitats. To maintain catfish populations, an understanding of channel catfish early-life habitat use is necessary. We quantified habitat use of juvenile channel catfish in the middle Mississippi River from 2004 through 2007 by trawling in main channel, channel border, island, and artificial structure habitat (i.e., river training structures or wing dikes) features throughout the sampling reach (N= 878 trawls; N= 538 juvenile channel catfish). Channel catfish occurred most frequently in island and off-channel habitats. Few juvenile channel catfish were trawled in the main channel. All macrohabitat features were used by a broad size range of juvenile channel catfish, with the exception of the main channel, where only larger juvenile channel catfish were captured. Within each habitat, juvenile channel catfish catch rates were highest in sand substrate, low velocity, and shallow depths. Channel catfish in the middle Mississippi River use a variety of habitats during early life. Maintaining existing habitats, creating habitats with these attributes, and coupling this with proper management will foster sustainability of the channel catfish population at current commercial and recreational fishing levels in the middle Mississippi River.

Habitat use by wild age-0 shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus was quantified by trawling macrohabitats (i.e., main channel, main-channel border, island, and artificial structures [e. g., wing dams]) in the middle Mississippi River during 1998-2007 (1,702 trawls; n = 1,507 age-0 sturgeon captured). Age-0 sturgeon catch rates were highest around artificial structures and island areas, while main-channel habitat provided the lowest catch rates. Moreover, size-selective macrohabitat analyses indicated that small age-0 sturgeon (i.e., majority < 50 mm total length) were located in channel-border dike and island side-channel macrohabitats, while all other macrohabitats were occupied by small and large age-0 sturgeon. Furthermore, our analyses indicated that age-0 sturgeon mesohabitat use within macrohabitats was influenced by depth, substrate, and bottom velocity. Low velocity (i.e., similar to 0.1 m/s), moderate depths (i.e., 2-5 m), and sand substrate were positively related to age-0 sturgeon relative abundance. As such, instream habitat modifications that provide the correct combination of macrohabitats with suitable mesohabitats may hold high densities of age-0 shovelnose sturgeon and pallid sturgeon and may improve recruitment success.

Several studies have investigated the demographics of shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus in the Mississippi River through assessment of adult populations; however, comparatively few studies have examined the early life history of these species. Here, we describe a comprehensive 4-year study that examined the effects of water temperature and river stage on the mortality, abundance, hatch timing, and growth rates of age-0 Scaphirhynchus spp. sturgeon in the middle Mississippi River. We trawled island areas every 7-10 d from April to August 2004-2007. We captured 1,256 individuals ranging from 10 to 193 mm total length over the 4-year study. Mean age-0 sturgeon growth rates ranged from 1.42 to 1.50 mm/d over the 4 years; however, growth rates did not differ among years. Individuals hatched over a 25-65-d period, and peak hatch dates were between 10 and 20 May in all years. Moreover, hatch timing possibly coincided with optimum spawning temperatures of 17-20 degrees C and an increase in river stage. Abundance appeared to be regulated by river stage; longer durations of high water were related to higher relative abundance. Furthermore, mortality increased with the number of days on which water temperature exceeded 28 degrees C. Based on these data, management strategies may need to ensure sturgeon hatching success and subsequent survival through optimizing hydrologic and thermal regimes that occur during the early life stage.

How paddlefish Polyodon spathula early-life history dynamics affect recruitment is relatively unknown. We quantified factors affecting age-0 paddlefish abundance, hatch time, growth, and survival in an unimpounded reach of the Mississippi River during 2000-2008. We trawled several habitats, collecting 2,074 age-0 paddlefish from 10 to 170 mm total length. Paddlefish hatch timing varied across years (30-60 d), generally commencing in the middle of April and ending in June when a threshold water temperature was reached and river stage variability increased. Correspondingly, an analysis of covariance revealed a strong interaction between year and habitat for catch per unit effort in the small (10-50 mm) (P = 0.025) and medium (51-100 mm) (P = 0.040) size-classes, indicating that habitat preferences were likely influenced by year. However, no relations between these variables in the large size-class (>100 mm) existed (P = 0.88). Age-0 paddlefish growth rates differed among years (i.e., 1.87-3.31 mm/d) and were positively related to water temperature (r = 0.64; P = 0.083). Mortality rates varied by year (range = -0.26 to -0.57) and were positively correlated with the number of days water temperature was below 28 degrees C during April 15 through July 15 (r = 0.67, P = 0.070). Water temperature and river stage variability may regulate early-life dynamics of paddlefish. Early-life history dynamics are likely interrelated with habitat conditions present in the river. The highest catch rates of young paddlefish were on the main channel side and side channel of islands, suggesting that these habitats are important to paddlefish. Within these habitats, paddlefish frequently occupied moderate velocities (i.e., 0.4-0.6 m/s), moderate depths (i.e., 3-5 m), and sand substrate.

Sampling has been conducted in small to large rivers of the Midwest and northeastern United States to determine the usfulness of a modified Missouri trawl designed to increase species detection of small-bodied fish species. We modified the Missouri trawl, which is a 4.8 m standard two-seam slingshot balloon trawl with a small mesh cover, by reducing the size (to a 2.44 m) and cover. The modified Missouri trawl (a.k.a. the mini-Missouri trawl) increased the number of small-bodied aquatic species of concern captured over that of previously used gears. For instance, shoal chub (Macrhybopsis hyostoma) had only been captured in the St. Croix River of Minnesota at three locations since 1960, yet we sampled it at 14 new locations in September, 2004 employing this methodology. Because of our success in these diverse and numerous systems, we believe this is a useful methodology for sampling the benthic fish community in many aquatic systems when other sampling methods are difficult to use because of water depths and/or velocities.

We evaluated the efficacy of three gears commonly used to sample shovelnose sturgeon Scaphirhynchus platorynchus, pallid sturgeon S. albus, and lake sturgeon Acipenser fulvescens in large rivers. We stratified habitats and randomly sampled sites with trawls, gill nets, and trotlines, in the middle Mississippi River from June 2003 through May 2005 (N = 3,476 samples). A total of 3,523 shovelnose sturgeon, 31 pallid sturgeon, and 13 lake sturgeon were captured. When sample sizes were adequate (based on power analysis), we used a mixed analysis of variance (ANOVA), procedure to determine the relative impact of season and gear type on sturgeon catch per unit effort (CPUE). Kolmogorov-Smirnov tests were used to determine whether the length frequency distributions for each species differed among gears. Overall, the power analyses indicated that there were adequate sample sizes for comparing standardized CPUE for shovelnose sturgeon among seasons; however, too few pallid or lake sturgeon were collected to make statistical comparisons. Shovelnose sturgeon catch rates varied among gears and seasons: season and gear type interacted in the ANOVA model. Among gear types, 5.08-cm gill nets produced the highest standardized CPUE, and catch rates were highest during spring. The length frequency distributions of shovelnose sturgeon depended on gear type. Shovelnose sturgeon can be sampled in large rivers using stratified random sampling with this combination of gear. However, pallid sturgeon and lake sturgeon may be too rare to sample with this approach.

The pallid sturgeon (Scaphirhynchus albus) was not described until 1905, when it was commonly caught by commercial fishers. This species began to decline in the early 1900s presumably because of overbarvest and habitat degradation. The U.S. Fish and Wildlife Service listed S. albus as an endangered species in 1990. Because S. albus live. in deep, turbid rivers that are difficult to sample, very little is known about its reproductive timing and spawning habitat. The act of spawning has never been observed in nature. Captures of wild young S. albus verifying natural reproduction are rare, the last being a 4-year-old fish taken in 1978. In this paper, we describe the first collection of a larval S. albus from the wild and subsequent larval collections in the Mississippi River from 1998 to 2000 using a modified slingshot balloon trawl (the Missouri Trawl) designed to capture small fishes in deep, turbulent rivers. We captured larval Scaphirhynchus spp., including verified S. albus, in association with island habitats often in heavy detritus, especially at downstream tips. We postulate that Scaphirhynchus spp. spawned at the heads of islands upstream from where we collected larvae, but we cannot be certain. The capture of larval S. albus verifies reproduction possibly from the lower Missouri River to the upper and lower Mississippi River. However, we found no evidence of recruitment of S. albus from 1998 to 2000 as we were unable to capture juveniles after 374 trawl hauls that captured over 21 735 fish.

We conducted a study from 1998 to 2001 to determine the efficacy of a benthic trawl designed to increase species detection and reduce the incidence of zero catches of small-bodied fishes. We modified a standard two-seam slingshot balloon trawl by covering the entire trawl with a small-mesh cover. After completing 281 hauls with the modified (Missouri) trawl, we discovered that most fish passed through the body of the standard trawl and were captured in the cover. Logistic regression indicated no noticeable effect of the cover on the catch entering the standard portion of the modified trawl. However, some fishes (e.g., larval sturgeons Scaphirhynchus spp. and pallid sturgeon S. albus) were exclusively captured in the small-mesh cover, while the catch of small-bodied adult fish (e.g., chubs Macrhybopsis spp.) was significantly improved by use of the small-mesh cover design. The Missouri trawl significantly increased the number and species of small-bodied fishes captured over previously used designs and is a useful method for sampling the benthic fish community in moderate- to large-size river systems.

We investigated variation of incidentally captured turtle mortality in response to environmental factors and passive fishing techniques. We used Long Term Resource Monitoring Program (LTRMP) data collected from 1996 to 2001 in the unimpounded upper Mississippi River (UMR) adjacent to Missouri and Illinois, USA. We used a principle components analysis (PCA) and a stepwise discriminant function analysis to identify factors correlated with mortality of captured turtles. Furthermore, we were interested in what percentage of turtles died from passive fishing techniques and what techniques caused the most turtle mortality. The main factors influencing captured turtle mortality were water temperature and depth at net deployment. Fyke nets captured the most turtles and caused the most turtle mortality. Almost 90% of mortalities occurred in offshore aquatic areas (i.e., side channel or tributary). Our results provide information on causes of turtle mortality (as bycatch) in a riverine system and implications for river turtle conservation by suggesting management strategies to reduce turtle bycatch and decrease mortality of captured turtles.