Catfish are popular with anglers fishing southeastern South Dakota rivers, and a group of anglers has expressed concern about the perceived overharvest of trophy‐size catfish. However, existing data are insufficient for determining whether Flathead Catfish Pylodictis olivaris and Channel Catfish Ictalurus punctatus are being overharvested. Our objective was to determine the population dynamics of Flathead and Channel catfish and model potential outcomes of length‐based trophy regulations (one fish and no fish harvested over 610 mm) in the lower James River, South Dakota. Multiple gears were used to collect Flathead Catfish (low‐frequency electrofishing and trotlines) and Channel Catfish (baited hoop nets and low‐frequency electrofishing) during 2018, and samples were augmented with angler‐caught catfish collected from three angling tournaments. Pectoral spines were removed from a subsample of fish for age estimation; 305‐mm and larger fish received a Carlin dangler tag with a reward value of US$0, $10, or $100. Growth rates were slow to moderate for Flathead Catfish and moderate for Channel Catfish. Trophy‐size Flathead Catfish (TL ≥ 1,020 mm) were sampled, but few of the collected Channel Catfish exceeded preferred length (TL ≥ 610 mm). Total annual mortality was estimated at 25.7% for Flathead Catfish and 25.2% for Channel Catfish. Exploitation estimated from angler reward tag returns was less than 1% for each species. Yield‐per‐recruit models indicated that a regulation specifying one fish over 610 mm would slightly reduce yield for both species but would only increase the number of memorable‐length Flathead Catfish (860 mm) and Channel Catfish (710 mm) by less than 1%. A no‐harvest regulation would substantially reduce yield of Flathead Catfish and would increase the number of memorable‐length Flathead Catfish by approximately 2% and Channel Catfish by less than 1%. Information obtained during this study suggests that current Flathead and Channel Catfish populations have limited trophy potential and that length‐based trophy regulations would have limited impact on the abundance of large catfish in the lower James River.

Sampling is often standardized with regard to time and space to monitor population characteristics. Effective sampling of large reservoirs can be complicated by the inherit bias of habitat variability along the reservoir gradient. Our objective was to assess spatial and seasonal distribution patterns of target and nontarget fish species in a large reservoir to identify potential sources of bias. A multitude of fish community and habitat characteristics were measured during seasonal (spring, summer, and fall) gill‐net surveys in 2015 and 2016 at Lake McConaughy, Nebraska. Spatial assessments along the longitudinal gradient (up‐reservoir to down‐reservoir) and between opposing shorelines were made for fish metrics from the seven most common species, and associations between species‐specific relative abundance and habitat data were examined. Spatial differences in relative abundance and size structure occurred for nearly all species, with the greatest spatial variability occurring between the upper and lower reservoir zones, but few strong correlations were observed between species‐specific relative abundances and habitat data. Seasonal differences occurred in relative abundance and size structure for most species, and size structure was lowest in the fall for most species. To reduce the impact of spatial variability, we determined the minimum required sampling effort to achieve precise estimates of mean catch per net‐night using two resampling strategies, with 16 or fewer gill‐net sets required for five of seven species and 14 or fewer required if a stratified random approach is utilized. This research quantifies the extent of spatial and temporal variability in standardized sampling on a large reservoir and provides novel insight for managers of similar systems considering a stratified random approach to reduce sampling effort while maintaining desired levels of precision.

Background One of the most important considerations for acoustic telemetry study designs is detection probability between the transmitter and the receiver. Variation in environmental (i.e., wind and flow) and abiotic (i.e., bathymetry) conditions among aquatic systems can lead to differences in detection probability temporally or between systems. In this study we evaluate the effect of distance, receiver mount design, transmitter depth, and wind speed on detection probabilities of two models of acoustic transmitters in a mid-sized river. InnovaSea V16-6H (hereafter V16) and V13-1L (hereafter V13) tags were deployed in the James River, SD at 0.36 m (deep) and 2.29 m (V16 tag) or 1.98 m (V13 tag; shallow) above the benthic surface downstream of InnovaSea VR2W stationary receivers at distances of 100, 200, or 300 m. We used two receiver mount designs that included a fixed position within a PVC pipe on the downstream side of a bridge piling or a metal frame deployed in the middle of the river channel. Tags were deployed for 72 h at each location, and hourly detections were summarized. We evaluated downstream distance, receiver mount design, tag depth, and wind effects on tag detection using Bayesian logistic regression. Results Detection probability decreased as distance increased for all combinations of tag types and mount designs and varied from nearly 100% at 100 m to less than 10% at 300 m. The V16 transmitter had greater detection probability by the receiver mounted in the pipe than in the midriver frame. For both mounts, the deep V16 transmitter had greater detection probability than the V16 shallow transmitter. Detection probability of the V13 transmitter was similar between receiver mounts or transmitter depths. Wind speed had a negative impact on detection probabilities of both transmitter types and depths, except the deep V16 transmitter. Conclusions Deploying acoustic receivers in PVC pipes rather than midriver frames provided greater downstream detection probabilities for V16 transmitters under conditions evaluated in this study. In addition, V16 transmitters had greater detection probabilities when positioned deep within the water column rather than near the surface. We also demonstrated that wind speed can have a negative impact on detection probabilities.

Blue Sucker Cycleptus elongatus is a species of concern across much of its native range due to population fragmentation and habitat loss. A primary component of managing this species is monitoring various population characteristics, including size structure. A common way to quickly index population size structure is to calculate the proportional size distribution (PSD). However, no standard length categories have been established for Blue Suckers, precluding the use of this index. We used databases, literature searches, field guides, and sampling records to find the largest recorded Blue Sucker. The maximum size Blue Sucker on record was 93 cm, so we propose the following standardized length categories: stock = 23 cm, quality = 38 cm, preferred = 51 cm, memorable = 59 cm, and trophy = 74 cm. We estimated mean values for PSDs using a Bayesian generalized linear mixed model, with a multinomial likelihood for populations of Blue Suckers from six rivers: the James, Big Sioux, Colorado, Red, Wabash, and Missouri. Most of these populations exhibited large size structures except for the James River. The length categories that we derived from the values for PSD should provide an additional tool for evaluating spatial and temporal changes in the size structure of Blue Sucker populations when monitoring the status of this species of concern.

Invasive species represent a substantial threat to aquatic systems, and aquaculture operations provide a vector for their transportation between waters. Moving large volumes of water during fish spawning or trap‐and‐transfer operations increases the risk of transporting invasive bivalve larvae, particularly from sources experiencing nondetection error. This study evaluated the effectiveness of two portable filter systems at reducing or eliminating zebra mussel Dreissena polymorpha and Asian clam Corbicula fluminea veligers from an infested water source. A small setup was assessed at intervals to 1,420 L using combinations of 20‐ and 5‐μm filters arranged in tandem, whereas a large setup was tested at intervals to 7,041 L with combinations of 30‐ and 5‐μm tandem filters operating at two pressure ranges. Zero veligers were observed in 36 small‐setup filtered water samples. Four zebra mussel veligers and zero Asian clam veligers were observed in 60 large‐setup samples. Total zebra mussel and Asian clam counts from 31 unfiltered control samples were 27,846 and 1,095, respectively. Overall, both filter systems were highly effective at removing zebra mussel and Asian clam veligers and represent simple, cost‐effective safeguards against nondetection error of aquatic invasive species in waters used for aquaculture practices.

Spawning habitat assessments often focus on substrate composition, but few studies have predicted shoal substrates by using environmental factors. We developed a model for predicting shoal substrates in Belle Lake, Minnesota, using wind fetch and shoreline relief characteristics. Percent composition of four substrate classes (silt, sand, gravel, and rock), water depth estimated at 1 m from shore (shoal slope), effective wind fetch measured using a GIS model, and riparian bank height derived from LIDAR imaging were determined at 50 transects. Classification and regression tree (CART) analysis grouped substrates into categories, and general additive modeling described the effects of three predictor variables on the percent composition of substrate classes. The CART analysis correctly grouped 39 of 50 transects into four categories, and misclassifications primarily resulted from the movement of sand. Effective fetch most influenced silt (low fetch) and rock (high fetch) substrate classes, shoal slope was predictive of rock, and riparian height was useful in distinguishing sand from gravel. These results demonstrate the utility of a single empirical model for determining shoal substrate composition. Fisheries managers can use this technique to determine potential fish spawning locations and identify potential areas for habitat restoration or protection projects. Received December 5, 2016; accepted May 5, 2017 Published online July 19, 2017

The ratio of female to male Walleye Sander vitreus across the spatial scale of large reservoirs and during non-spawning times receives little attention, even though standardized sampling occurs during this time. This study evaluated whether the proportion of female Walleye collected from seasonal sampling at different spatial areas within a large reservoir fell within the 0.450-0.550 range, which would closely reflect a 1:1 female-to-male sex ratio. We used a Bayesian generalized linear mixed effects model with a binomial likelihood to assess the proportion of Walleye using season (spring and fall) and reservoir zone (riverine, transitional, and lacustrine) as fixed effects and year (2015 and 2016) as random effects. We collected a total of 2,163 Walleye using standardized Nebraska Game and Parks Commission gill netting methodology, and sex was determined on a random subsample of fish (n = 989) collected throughout each reservoir zone. There was no meaningful deviation from the 0.450-0.550 range in the mean posterior estimate of the proportion of female Walleye caught in the riverine and transitional zones during either spring or fall. The mean (SD) posterior estimate of the proportion of female Walleye in the lacustrine zone was 0.182 (0.024) in the spring and 0.621 (0.032) in the fall. These results are consistent with previous observations of increased male presence near spawning locations in the spring and demonstrate that increased fall female catch in the lacustrine zone could potentially bias sampling results. This study provides further insight into the distribution of sexes across the spatial gradient of a large Great Plains reservoir and demonstrates a need to sex Walleye during standardized fall surveys.

Fish samples collected during different times of the year can be subject to various biases, but the influence of sampling during different seasons on population dynamics and yield metrics in large reservoirs is not well reported. This study compared the age structure, growth, mortality, and yield estimates of Channel Catfish Ictalurus punctatus and Walleye Sander vitreus collected during spring and fall with standardized gill netting in a large Nebraska reservoir. Fish were sampled using the Nebraska Game and Parks Commission standardized gill net survey methodology. Ages were estimated from pectoral spines of Channel Catfish and sagittal otoliths of Walleye, age-length keys were derived, and mean spring and fall ages were compared with t -tests. Spring and fall von Bertalanffy growth curves were compared with likelihood-ratio tests, and mortality estimates from weighted catch curves were compared with an analysis of variance. Spring and fall yield estimates derived from yield-per-recruit models were visually compared to assess the impact of variable population dynamics estimates. Estimates of mean age, growth coefficient ( K ), mean asymptotic length ( L ∞ ), total annual mortality ( A ), and yield of Channel Catfish did not differ between spring and fall. Conversely, older age structure of Walleye in spring resulted in lower estimates of A and higher yield than in fall. Estimates of L ∞ and K differed between spring and fall for female Walleye, and L ∞ , K , and t 0 estimates varied between spring and fall for male Walleye. Fall yield estimates were substantially lower than spring estimates for both male and female Walleye. These results demonstrate that the season when samples are collected can impact population dynamics estimates for certain species while others remain relatively unaffected.