We investigated fish assemblage structure in engineered (rip-rap) and natural habitats (log jams and mud banks) in the Kansas River USA to determine if natural structures had higher abundance and diversity of fishes at a local spatial scale. A total of 439 randomly selected sites were boat electrofished from May to August 2005 and 2006. Mean species diversity and richness were significantly higher in rip-rap than log jams and mud banks. Mean relative abundance (CPUE; number of fish collected per hour electrofishing) of six of the 15 most common fishes (>1% of total catch) were most abundant in rip-rap, two were most abundant in log jams, and none in mud banks. Rip-rap had the highest relative abundance of fluvial specialist and macrohabitat generalists, whereas mean CPUE of fluvial dependents was highest in log jams. Although a discriminant function analysis indicated that nine size classes (eight species) discriminated among three habitat types, the high misclassification rate (38%) suggested a high degree of fish assemblage overlap among the habitats. Although previous work has suggested that engineered structures (rip-rap) and urbanization are linked to reduced biotic diversity or reduced growth of fish species, our results suggest that at a local scale rip-rap may not have the same negative impacts on fish assemblages. Published in

Blue sucker, Cycleptus elongatus (Le Sueur), was sampled in the Kansas River, Kansas, USA to determine how relative abundance varies spatially and growth compares to other populations. Electric fishing was conducted at 36 fixed sites during five time periods from March 2005 to January 2006 to determine seasonal distribution. An additional 302 sites were sampled in summer 2005 to determine distribution throughout the river. A total of 101 blue sucker was collected ranging from 242 to 782 mm total length and 1-16 years old. Higher catch rates were observed in upper river segments and below a low-head dam in lower river segments, and catch rates were higher during November in the upriver sites. Kansas River blue sucker exhibited slower growth rates than other populations in the Great Plains including populations as far north as South Dakota.

We used an integrated assessment model to examine effects of flow from Glen Canyon Dam, Arizona, USA, on recruitment of nonnative rainbow trout ( Oncorhynchus mykiss ) in the Colorado River and to estimate downstream migration from Glen Canyon to Marble Canyon, a reach used by endangered native fish. Over a 20-year period, recruitment of rainbow trout in Glen Canyon increased with the annual flow volume and when hourly flow variation was reduced and after two of three controlled floods. The model predicted that approximately 16 000 trout·year–1 emigrated to Marble Canyon and that the majority of trout in this reach originate from Glen Canyon. For most models that were examined, over 70% of the variation in emigration rates was explained by variation in recruitment in Glen Canyon, suggesting that flow from the dam controls in large part the extent of potential negative interactions between rainbow trout and native fish. Controlled floods and steadier flows, which were originally aimed at partially restoring conditions before the dam (greater native fish abundance and larger sand bars), appear to have been more beneficial to nonnative rainbow trout than to native fish.

Populations of flathead catfish Pylodictis olivaris in four reaches of the Kansas River, Kansas, were examined to evaluate the effects of three minimum length limits (305 [the minimum size that anglers are willing to harvest], 610, and 762 mm total length [TL]) on population size structure and number harvested over a 30-year simulation. We used electrofishing and hoopnetting to capture and tag flathead catfish throughout the Kansas River from [2005][2006]. Current exploitation (u) based on tag returns was probably less than 10%, and total annual mortality A ranged from 14% to 28% across all reaches. Increased river access and promotion of this fishery may increase u in the future, so model simulations were conducted with conditional natural mortality (cm) and u ranging from 10% to 40%. Proportional stock density (PSD) and the relative stock density of preferred-length fish (RSD-P) substantially declined (by .25% and .15%, respectively) as u increased with the 305-mm TL limit over the 30-year simulation. The PSD showed similar trends across all reaches, indicating that use of different regulations among reaches was not necessary and that differences in growth among reaches were less influential than u and cm. No substantial differences were observed in size structure under the 610-and 762-mm TL limits among reaches, but under a 762-mm TL limit anglers would have to sacrifice about 42% of the number harvested under the current cm level. Mortality caps revealed that each reach could sustain an A of about 60% and 55% to maintain current PSD and RSD-P levels, respectively; this result suggests that quality flathead catfish size structure can be preserved. Our results show that the effects (or lack thereof) on flathead catfish and other sport fishes should be evaluated before harvest restrictions are implemented.

Long-term fish monitoring in the Colorado River below Glen Canyon Dam is an essential component of the Glen Canyon Dam Adaptive Management Program (GCDAMP). The GCDAMP is a federally authorized initiative to ensure that the primary mandate of the Grand Canyon Protection Act of 1992 to protect resources downstream from Glen Canyon Dam is met. The U.S. Geological Survey's Grand Canyon Monitoring and Research Center is responsible for the program's long-term fish monitoring, which is implemented in cooperation with the Arizona Game and Fish Department, U.S. Fish and Wildlife Service, SWCA Environmental Consultants, and others. Electrofishing and tagging protocols have been developed and implemented for standardized annual monitoring of Colorado River fishes since 2000. In 2009, sampling occurred throughout the river between Lees Ferry and Lake Mead for 38 nights over two trips. During the two trips, scientists captured 6,826 fish representing 11 species. Based on catch-per-unit-effort, salmonids (for example, rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta)) increased eightfold between 2006 and 2009. Flannelmouth sucker (Catostomus latipinnis) catch rates were twice as high in 2009 as in 2006. Humpback chub (Gila cypha) catches were low throughout the 10-year sampling period.

[1] Nutrient dynamics in rivers are central to global biogeochemistry. We measured ammonium (NH 4 + ) uptake, metabolism, nitrification, and denitrification in the thalweg, the river region of greatest flow, of the Kansas River (discharge = 14,360 L/s). We estimated gross and net uptake with a depleted 15 N-NH 4 + release, metabolism with diel O 2 measurements, and denitrification with dissolved N 2 measurements. Net ecosystem production was negative. Net NH 4 + uptake length was 2.1 km when concentrations were elevated, and gross uptake length was 1.9 km at ambient concentrations. Gross uptake rate measurements were comparable to estimates made using extrapolations from data obtained from streams (systems with 1/10th or less the discharge). Calculated lengths were maximal because the isotope pulse was primarily confined to the thalweg and not the shallow side channels or backwaters. Denitrification and nitrification rates were below detection. In the Kansas River, rates of N cycling are driven by heterotrophic processes, and considerable processing of N, particularly NH 4 + uptake, occurred over a few kilometers of river length, with net uptake rates of NH 4 + increasing with greater NH 4 + concentrations.

We investigated the spatial variation of flathead catfish (Pylodictis olivaris) relative abundance and growth in the 274 km long Kansas River to determine if population dynamics of catfish are related to urbanization. Electrofishing was conducted at 462 random sites throughout the river in summer, [2005][2006] to collect fish. Relative abundance of age 1 fish ( 200 mm), subadult (>200-400 mm) and adult fish (>400 mm) ranged from 0.34 to 14.67 fish h À1, mean length at age 1 was 165 (range: 128-195) mm total length (TL) and mean length at age 3 was 376 mm TL (range: 293-419 mm TL). The proportion of land use within 200 m of the river edge was between 0 and 0.54 urban. River reaches with high relative abundance of age 1 flathead catfish had high relative abundance of subadult and adult catfish. River reaches with fast flathead catfish growth to age 1 had fast growth to age 3. High urban land use and riprap in the riparian area were evident in river reaches near the heavily populated Kansas City and Topeka, Kansas, USA. Reaches with increased number of log jams and islands had decreased riparian agriculture. Areas of low urbanization had faster flathead catfish growth (r ¼ 0.67, p ¼ 0.005). Relative abundance of flathead catfish was higher in more agricultural areas (r ¼ À0.57, p ¼ 0.02). Changes in land use in riverine environments may alter population dynamics of a fish species within a river. Spatial differences in population dynamics need to be considered when evaluating riverine fish populations. Published in

The Lees Ferry reach of the Colorado River, a 25-kilometer segment of river located immediately downstream from Glen Canyon Dam, has contained a nonnative rainbow trout (Oncorhynchus mykiss) sport fishery since it was first stocked in 1964. The fishery has evolved over time in response to changes in dam operations and fish management. Long-term monitoring of the rainbow trout population downstream of Glen Canyon Dam is an essential component of the Glen Canyon Dam Adaptive Management Program. A standardized sampling design was implemented in 1991 and has changed several times in response to independent, external scientific-review recommendations and budget constraints. Population metrics (catch per unit effort, proportional stock density, and relative condition) were estimated from 1991 to 2009 by combining data collected at fixed sampling sites during this time period and at random sampling sites from 2002 to 2009. The validity of combining population metrics for data collected at fixed and random sites was confirmed by a one-way analysis of variance by fish-length class size. Analysis of the rainbow trout population metrics from 1991 to 2009 showed that the abundance of rainbow trout increased from 1991 to 1997, following implementation of a more steady flow regime, but declined from about 2000 to 2007. Abundance in 2008 and 2009 was high compared to previous years, which was likely the result of increased early survival caused by improved habitat conditions following the 2008 high-flow experiment at Glen Canyon Dam. Proportional stock density declined between 1991 and 2006, reflecting increased natural reproduction and large numbers of small fish in samples. Since 2001, the proportional stock density has been relatively stable. Relative condition varied with size class of rainbow trout but has been relatively stable since 1991 for fish smaller than 152 millimeters (mm), except for a substantial decrease in 2009. Relative condition was more variable for larger size classes, and substantial decreases were observed for the 152-304-mm size class in 2009 and 305-405-mm size class in 2008 that persisted into 2009.