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Commercial fisheries are commonly used to manage nuisance fishes in freshwater systems, but such efforts are often unsuccessful. Strategies for successfully controlling a nuisance population of common carp Cyprinus carpio by pulsed commercial harvest were evaluated with a combination of (1) field sampling, (2) population estimation and CPUE indexing, and (3) simulation using an exponential semidiscrete biomass dynamics model (SDBDM). The range of annual fishing mortalities (F) that resulted in successful control (F = 0.244–0.265) was narrow. Common carp biomass dynamics were sensitive to unintentional underharvest due to high rates of surplus production and a biomass doubling time of 2.7 years. Simulations indicated that biomanipulation never achieved successful control unless supplemental fishing mortality was imposed. Harvest of a majority of annual production was required to achieve successful control, as indicated by the ecotrophic coefficient (EC). Readily available biomass data and tools su...

Land use changes and channelization of streams in the deep loess region of western Iowa have led to stream channel incision, altered flow regimes, increased sediment inputs, decreased habitat diversity and reduced lateral connectivity of streams and floodplains. Grade control structures (GCSs) are built in streams to prevent further erosion, protect infrastructure and reduce sediment loads. However, GCS can have a detrimental impact on fisheries and biological communities. We review three complementary biological and hydraulic studies on the effects of GCS in these streams. GCS with steep (≥1:4 rise:run) downstream slopes severely limited fish passage, but GCS with gentle slopes (≤1:15) allowed greater passage. Fish assemblages were dominated by species tolerant of degradation, and Index of Biotic Integrity (IBI) scores were indicative of fair or poor biotic integrity. More than 50% of fish species had truncated distributions. After modification of GCS to reduce slopes and permit increased passage, IBI scores increased and several species were detected further upstream than before modification. Total macroinvertebrate density, biomass and taxonomic diversity and abundance of ecologically sensitive taxa were greater at GCS than in reaches immediately upstream, downstream or ≥1km from GCS. A hydraulic study confirmed results from fish passage studies; minimum depths and maximum current velocities at GCS with gentle slopes (≤1:15) were more likely to meet minimum criteria for catfish passage than GCS with steeper slopes. Multidisciplinary approaches such as ours will increase understanding of GCS-associated factors influencing fish passage, biological assemblage structure and other ecological relationships in streams. Copyright © 2011 John Wiley & Sons, Ltd.

Riparian buffers can improve stream water and habitat quality by reducing non-point-source pollution (e.g., nutrients and sediment), increasing canopy cover and thereby reducing water temperature, and contributing allochthonous organic matter (e.g., leaf litter and woody debris). However, the influence of riparian buffers on biotic assemblages in streams is poorly understood, particularly in the Midwestern United States. In this study, we evaluated the effects of riparian buffers on instream habitat, fish assemblage structure, and population characteristics (i.e., the growth of two small-bodied species) in three streams in central Iowa. The streams were surveyed at two spatial scales; specifically, 41 reaches were sampled and 247 macrohabitat types (i.e., pool, riffle, and run) were subsampled in the summer of 2007. Fish assemblage structure data were summarized into separate data sets by the relative abundance of individual species (i.e., fish per minute of electrofishing) and guilds (e.g., trop...

Grade control structures (GCSs) are commonly used in streams of western Iowa to control bank erosion and channel headcutting but may be barriers to fish passage. From May 2002 to May 2006, we used mark–recapture methods to evaluate fish passage over a total of five GCSs, ranging in slope (run : rise) from 13:1 to 18:1 in Turkey Creek, Cass County, Iowa. Three structures, over which limited fish movement was documented from 2002 to 2004, were modified in the winter of 2004–2005 to facilitate fish passage. Before modification, the majority of recaptured fish were recaptured at the station where they were originally marked; only 1% displayed movement between sites and either upstream or downstream over a GCS. After modification fish passage improved, 14% of recaptured fish displayed movement either upstream or downstream over a GCS. Individuals of four target species—channel catfish Ictalurus punctatus, yellow bullhead Ameiurus natalis, black bullhead A. melas, and creek chub Semotilus atromaculatus...

Nearly 400 rock rip-rap grade control structures (hereafter GCS) were recently placed in streams of western Iowa, USA to reduce streambank erosion and protect bridge infrastructure and farmland. In this region, streams are characterized by channelized reaches, highly incised banks and silt and sand substrates that normally support low macroinvertebrate abundance and diversity. Therefore, GCS composed of rip-rap provide the majority of coarse substrate habitat for benthic macroinvertebrates in these streams. We sampled 20 sites on Walnut Creek, Montgomery County, Iowa to quantify macroinvertebrate assemblage characteristics (1) on GCS rip-rap and at sites located (2) 5–50 m upstream of GCS, (3) 5–50 m downstream of GCS and (4) at least 1 km from any GCS (five sites each). Macroinvertebrate biomass, numerical densities and diversity were greatest at sites with coarse substrates, including GCS sites and one natural riffle site and relatively low at remaining sites with soft substrates. Densities of macroinvertebrates in the orders Ephemeroptera, Trichoptera, Diptera, Coleoptera and Acariformes were abundant on GCS rip-rap. Increases in macroinvertebrate biomass, density and diversity at GCS may improve local efficiency of breakdown of organic matter and nutrient and energy flow, and provide enhanced food resources for aquatic vertebrates. However, lack of positive macroinvertebrate responses immediately upstream and downstream of GCS suggest that positive effects might be restricted to the small areas of streambed covered by GCS. Improved understanding of GCS effects at both local and ecosystem scales is essential for stream management when these structures are present. Copyright © 2007 John Wiley & Sons, Ltd.