Robert E. Colombo

Movement and Habitat Selection by Invasive Asian Carps in a Large River

Abstract 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 f...

Use of Ultrasound Imaging to Determine Sex of Shovelnose Sturgeon

Abstract 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.

Maturation and Reproduction of Shovelnose Sturgeon in the Middle Mississippi River

Abstract 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...

Declining Recruitment and Growth of Shovelnose Sturgeon in the Middle Mississippi River: Implications for Conservation

Abstract To determine how populations of shovelnose sturgeon Scaphirhynchus platorynchus are changing and may respond to poor environmental conditions, current commercial harvest of black-egg (sexually mature) females, and incidental mortality of males, we require annual information about sex-specific age structure as it relates to the recruitment of new cohorts. We sampled shovelnose sturgeon by use of gill nets (5-cm bar mesh) monthly during 2002-2006 in the Middle Mississippi River between Cairo, Illinois, and St. Louis, Missouri. We compared patterns of size and age structure over time and projected age structure and population size into the future. Sex ratio in 2005-2006 was 1.14:1.00 (416 males and 363 females; P = 0.06), deviating from the 1:1 ratio that occurred in 2002-2003. Annual mortality increased from 37% in 2002-2003 to 44% by 2005-2006. Female shovelnose sturgeon were larger than males. Across years, the population shifted toward longer, older fish, and growth in length declined. Recruitme...

Habitat Selection and Movement of Naturally Occurring Pallid Sturgeon in the Mississippi River

Abstract 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 populations 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 dike...

Metal accumulation and evaluation of effects in a freshwater turtle

A variety of contaminants have been detected in aquatic and terrestrial environments around the Paducah Gaseous Diffusion Plant (PGDP), Kentucky. The presence of these contaminants at the PGDP may pose a risk to biota, yet little is known about the bioaccumulation of contaminants and associated effects in wildlife, especially in aquatic turtles. The current study was initiated to evaluate: (1) the accumulation of heavy metals (Cd, Cr, Cu, Pb, and Hg) in aquatic ecosystems associated with the PGDP using red-eared slider turtle (Trachemys scripta elegans) as biomonitors; (2) maternal transfer of heavy metals; and (3) potential hematological and immunological effects resulting from metal accumulation. A total of 26 turtles were collected from 7 ponds located south, adjacent, and north of the PGDP. Liver Cu concentrations were significantly different among ponds and Cu concentrations in eggs were positively correlated with female Cu concentrations in kidney. The concentrations of heavy metals measured in turtle tissues and eggs were low and, based on previous studies of reptiles and established avian threshold levels of heavy metals, did not appear to have adverse effects on aquatic turtles inhabiting ponds near the PGDP. However, total white blood cell counts, heterophil to lymphocyte ratio, and phytohemagglutinin stimulation index were correlated with metal concentrations. Because other factors may affect the hematological and immunological indices, further investigation is needed to determine if these effects are associated with metal exposure, other contaminants, or disease.

Comparison of Channel Catfish Age Estimates and Resulting Population Demographics Using Two Common Structures

Abstract Sagittal otoliths and the articulating process of the pectoral spine have both been validated as accurate techniques for estimating the age of channel catfish Ictalurus punctatus (≤age 4). However, there is limited information on the relative precision of estimates from these two structures. Thus, we analyzed the precision of age estimates derived from otoliths and the articulating process of the pectoral spine and compared the dynamic processes (recruitment, growth, and mortality) resulting from those estimates. Aging structures were removed from 110 channel catfish captured from the Wabash River (river kilometers 550–9.6) via day–time electrofishing. The age estimation methodologies were similar to those described in previous studies. Agreement between the ages derived from the two structures was high; the average percent error was 8.4%, the coefficient of variation was 11.4, and the slope of the age bias plots did not differ from 1, indicating similar age assignments between structures. The co...

Seasonal Comparison of Catch Rates and Size Structure Using Three Gear Types to Sample Sturgeon in the Middle Mississippi River

Abstract 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...

Contrasting Population Demographics of Invasive Silver Carp between an Impounded and Free-Flowing River

AbstractExtensive research has been conducted on Silver Carp Hypopthalmicthys molitrix in the heavily modified Illinois River in the midwestern United States due to the potential for populations to enter the Great Lakes; however, little research has been conducted on populations in unimpounded rivers. The Wabash River is an unimpounded large river in the U.S. Midwest that may be a good model for studying Silver Carp in unregulated river ecosystems that could potentially be invaded if reproducing populations in the Great Lakes are established. In this study we compared population demographics of Silver Carp in the Wabash and Illinois rivers. Abundance was over three times greater in the Illinois than in the Wabash River, although Wabash River Silver Carp had significantly greater mean length, age, and condition and a higher growth rate than did Illinois River Silver Carp. Although the heavily modified and degraded environment in the Illinois River may have aided in the rapid expansion of Silver Carp, intra...

Gear-Specific Population Demographics of Channel Catfish in a Large Midwestern River

Abstract 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....