We evaluated the habitat use and movements of 50 adult bighead carp Hypophthalmichthys nobilis and 50 silver carp H. molitrix by means of ultrasonic telemetry during spring‐summer 2004 and 2005 to gain insight into the conditions that facilitate their establishment, persistence, and dispersal in the lower Illinois River (river kilometer 0‐130). Movement and habitat use were monitored with stationary receivers and boat‐mounted tracking. The relative availability of four macrohabitat categories (main channel, island side channel, channel border, and connected backwater) was quantified to determine selection; discriminant function analysis was used to evaluate changes in physical characteristics within each category. A flood pulse occurred in spring through early summer of 2004 but not 2005. Movement rates (km/week) of both species were positively correlated with flow but not with temperature. Including data from stationary receivers greatly increased estimates of daily movement. During low summer flow, both species typically selected channel borders and avoided the main channel and backwaters. Both species rarely occupied depths over 4 m, regardless of abiotic conditions. Flood pulses appear to trigger dispersal, while habitat use is only specific during low summer flow. Thus, movement prevention efforts (e.g., dispersal barriers) will require particular vigilance during late‐winter or spring flooding, and controlled removal (e.g., harvest) should be directed toward selected habitats during summer.

Within harvested populations, relationships between harvest intensity and reproductive responses are typically unclear, rendering regulatory decisions difficult. Harvest of the commercially important shovelnose sturgeon (Scaphirhynchus platorynchus) is increasing in the upper Mississippi River; standardized seasonal sampling revealed that adult abundance is declining. Relative density of annual cohorts varied negatively with historical harvest intensity (r 2 ¼ 0.84), suggesting that removal of mature adults is reducing the contribution of cohorts to population density. The results of simulation modeling suggest that this currently unregulated fishery is experiencing both growth and recruitment overfishing. Further, the current proposed multi-state minimum length regulation was insufficient to maintain a sustainable stock. Only a more conservative minimum length limit (685 mm) produced yields that were sustainable at the current level of mortality and provided room for the fishery to grow. The annual mortality rate of the sympatric, federally endangered pallid sturgeon (S. albus) was similar to that of the shovelnose sturgeon population, raising concerns that harvest-induced mortality is affecting this congener's vital rates.

Harvest of the shovelnose sturgeon, Scaphirhynchus platorynchus for caviar has increased. To determine whether populations can withstand increased harvest, detailed information regarding sexual demographics is needed. We describe gender and reproductive development of 306 shovelnose sturgeon from the Middle Mississippi River (River km 0-322) during September 2001 through December 2003. Using dissection and histology, we identified three of the four gonadal stages described previously for male lake sturgeon and all seven stages for females. Males reached maturity at a smaller size than did females. Gonads can be rapidly inspected for sex and stage of development for the shovelnose sturgeon. The sex ratio was not different from 1 : 1. Seven intersexual fish occurred. Female fecundity was positively related to body weight (number of eggs ¼ 30.24 · body weight ) 8392; P ¼ 0.013; r 2 ¼ 0.45) and weakly related to fork length (number of eggs ¼ 146.37 · fork length ) 66 176, P ¼ 0.053, r 2 ¼ 0.23).

Shovelnose sturgeon Scaphirhynchus platorynchus in the middle Mississippi River provide one of the last commercially viable sturgeon fisheries in the world, yet their maturation and reproduction have not been linked. During 2005 and 2006, we sampled adult and age‐0 shovelnose sturgeon to link age at maturation, the timing and periodicity of spawning, age‐0 sturgeon production, and the resulting age‐0 growth rates. Age at maturity was later than previous estimates, the minimum age of first maturation being 8 years for males and 9 years for females. Total egg count was slightly lower than previously reported (mean = 29,573 per female; SE = 2,472). Males and females typically spawned every 2 and 3 years, respectively. Peaks in mature fish coincided with rising river stages and water temperatures at which shovelnose sturgeon probably spawn. Peaks in spent adults followed. Age‐0 shovelnose sturgeon occurred during June and July 2005 and May and June 2006, confirming successful spawning. Age‐0 sturgeon grew between 0.69 and 1.69 mm total length/d; four distinct weekly cohorts occurred each year. During fall 2006, females contained ripe eggs, males were milting, and a single age‐0 sturgeon (total length = 55 mm) was captured, suggesting that shovelnose sturgeon spawn during fall as well as spring. Management must consider the protracted nature of spawning within seasons as well as differences in spawning activity between seasons.

During November 2002, 51 shovelnose sturgeon Scaphirhynchus platorynchus were sexed by ultrasound imaging using a portable ultrasonograph. We identified males with 96% accuracy (N = 25) and females with 80% accuracy (N = 25); one hermaphroditic individual was misidentified as a male. Overall, ultrasound imaging was 86% accurate. Sex in postspawned females was difficult to determine, 60% being misidentified as males (N = 5). Ultrasonography is an effective noninvasive method for sex determination that can be applied to other species of Acipenseriformes. Modern portable equipment expands its utility to field studies.

Various gear types have been used to sample populations of channel catfish Ictalurus punctatus in lotic systems. However, these gears produce different population characteristics (i.e., recruitment, growth, and mortality). We compared the population demographics of channel catfish in the Wabash River, Indiana, sampled with baited 25‐ and 32‐mm‐bar mesh hoop nets and three‐phase alternating current (AC) electrofishing. Based on catch per unit effort, the relative abundance of channel catfish sampled with 32‐mm hoop nets was lower than that of fish sampled with 25‐mm hoop nets and AC electrofishing. Each gear type also resulted in a different length frequency, mean length increasing progressively in sampling with 25‐mm hoop nets, 32‐mm hoop nets, and AC electrofishing. Similarly, age‐frequency distributions differed among gears. The 25‐mm hoop nets biased the age structure toward younger individuals (mean age = 2.5), whereas both 32‐mm hoop nets (mean age = 4.0) and AC electrofishing (mean age = 5.8) included older fish. Catch‐curve analysis generated different mortality rates for the three gear types, the mortality rate being highest (50%) in fish sampled with 25‐mm hoop nets. Gear‐specific size and age structures led to differences in von Bertalanffy statistics among the 25‐mm hoop nets and AC electrofishing, while the results for 32‐mm hoop nets were uninterpretable. Because the different gears led to conflicting parameter estimates, management practices based on sampling with single gears may be contradictory. Given the differences in gear selectivity, biologists need to approach management cautiously until calibration to the true size and age structure is conducted.

The pallid sturgeon Scaphirhynchus albus is a U.S. federally endangered species that occurs in the 320‐km middle Mississippi River (MMR). Historic in‐channel island habitat has vanished, and the extent of the population's range within the MMR is unknown. We surgically implanted ultrasonic transmitters in 88 adult pallid sturgeon (>600 mm fork length; mean = 791 mm) during 2002–2005 and used boat‐mounted hydrophones to quantify their seasonal use of major MMR habitat features (wing dikes, side channels, island side channel tips, tributaries, and main channel; total of 8,629 river kilometers monitored). Distance from habitat features (gravel bars, wing dikes, and island side channels) was quantified during spring, a period considered to be critical for many fish species. We quantified maximum seasonal movement of each fish in the entire MMR with stationary data‐logging hydrophones during 2004–2006. Combining data across years and seasons, we found that pallid sturgeon selected the tips of wing dikes over other habitat features. However, during spring pallid sturgeon moved from the tips of wing dikes to within about 100 m of known gravel bars. Maximum distance moved by pallid sturgeon varied the most in spring relative to other seasons. One pallid sturgeon moved through the entire study reach, and a few individuals left the MMR for the Missouri River or the lower Mississippi River. Unique flow and substrate characteristics of wing dikes probably emulated missing habitat complexity (i.e., in‐channel islands, deep scour holes, and sand bars). Other habitats such as gravel bars may be important during spring, although their contributions to reproduction, foraging, and survival of pallid sturgeon are unknown. The range of this pallid sturgeon population extends beyond the entire stretch of the MMR into other river basins; thus, the population requires rangewide management.

The natural flow regime of many rivers in the USA has been impacted by anthropogenic structures. This loss of connectivity plays a role in shaping river ecosystems by altering physical habitat characteristics and shaping fish assemblages. Although the impacts of large dams on river systems are well documented, studies on the effects of low‐head dams using a functional guild approach have been fewer. We assessed river habitat quality and fish community structure at 12 sites on two rivers; the study sites included two sites below each dam, two sites in the pool above each dam and two sites upstream of the pool extent. Fish communities were sampled from 2012 to 2015 using a multi‐gear approach in spring and fall seasons. We aggregated fishes into habitat and reproductive guilds in order to ascertain dams' effects on groups of fishes that respond similarly to environmental variation. We found that habitat quality was significantly poorer in the artificial pools created above the dams than all other sampling sites. Fast riffle specialist taxa were most abundant in high‐quality riffle habitats farthest from the dams, while fast generalists and pelagophils were largely restricted to areas below the downstream‐most impoundment. Overall, these dams play a substantial role in shaping habitat, which impacts fish community composition on a functional level. Utilizing this functional approach enables us to mechanistically link the effects of impoundments to the structure of fish communities and form generalizations that can be applied to other systems. Copyright © 2017 John Wiley & Sons, Ltd.