Boat Electrofishing Research Articles

Assessing Minnesota’s Changing Yellow Perch Populations Using Length‐Based Metrics

AbstractCatch rates of Yellow Perch Perca flavescens in standard gill‐net surveys conducted by the Minnesota Department of Natural Resources have declined since 1970, but it is unclear whether this trend was due to reduced abundance or to changes in size structure affecting catchability. Because the minimum capture length of standard gill nets may limit effective sampling of some populations, the objectives of this study were to determine if length‐based metrics could be used to characterize populations and their susceptibility to standard gill nets, if these metrics were correlated with a suite of abiotic and biotic variables, and if temporal trends in these metrics were evident. Data were collected from a broad size distribution of Yellow Perch sampled with standard gill nets, boat electrofishing, and small‐mesh gill nets in 17 lakes. Estimated length at 50% maturity (L50) for females varied up to 100 mm across lakes, with values as small as 70 mm documented in some populations. Female L50 from supplemental gears was significantly positively correlated with the average length of the 15 largest fish (Lmax) from all gears, and both of these metrics were positively correlated with standard gill‐net catch. Exploratory analysis of female L50 indicated that this metric was positively correlated with latitude and lake size and negatively correlated with water clarity. Additionally, a statewide analysis of Lmax conducted with standard gill‐net data from over 1,000 lakes found significant declines during the past 25 years, indicating that populations in Minnesota have likely shifted towards a smaller size structure, reducing catchability in standard gill nets. These results indicate that standard gill nets were ineffective for sampling some Yellow Perch populations and that length‐based metrics such as L50 and Lmax can be used to infer catchability in standard gear and to monitor populations through time.

Effects of Adult Biomass and Environmental Conditions on Bigheaded Carp Reproductive Output

AbstractBighead Carp Hypothalmichthys nobilis and Silver Carp Hypothalmichthys moltrix (hereafter collectively referred to as Bigheaded Carp) have spread throughout the majority of the Mississippi River since the 1970s. The current northern invasion edge of Bigheaded Carp in the Upper Mississippi River (UMR) spans between Pools 14 and 20 because of limited passage at Lock and Dam (LD) 19. Mechanisms limiting adult Bigheaded Carp abundance above LD19 are unknown but may be due in part to lack of reproductive success influenced by adult abundance and environmental factors. Our objective was to investigate how relative adult biomass and river temperature and discharge affect maximum annual Bigheaded Carp larval production in the UMR using a Ricker stock-recruitment model. Adult Bigheaded Carp relative biomass (kg/h) was estimated annually with boat electrofishing and larvae were collected every 10 d between May and August 2014–2017 in Pools 14–20 in the UMR. Adult relative biomass ranged from 0.0 to 880.9 kg/h, whereas maximum annual larval densities ranged from 0.0 to 2,869.4 larvae/m3. After accounting for variability among pools and years, the most supported linear Ricker stock-recruitment model indicated the number of recruits per spawner decreased with increasing adult relative biomass and increased with mean discharge. Our results highlight the importance of adult biomass and river discharge conditions for reproduction of Bigheaded Carp along leading edges of invasion. Management strategies that aim to maintain low adult abundance where reproduction is not yet occurring could help limit population increases via reproduction, whereas reducing high adult biomass (e.g., commercial harvest, barriers) may result in greater Bigheaded Carp reproductive output in the UMR.

Using mark-recapture techniques to assess factors affecting survival of fall stocked walleye Sander vitreus in two Iowa lakes

Stocking walleye Sander virteus is a common management technique to supplement populations where natural reproduction is limited. However, numerous factors can influence the survival of fall stocked walleye including environmental conditions, predation, and stocked walleye total length (TL), condition, and foraging ability. The relative effects of these factors on survival of stocked walleye are challenging to evaluate and rarely assessed simultaneously. Our objective was to determine factors that influence survival rates of stocked fingerling walleye (98−287 mm TL) from stocking until ice cover in two Iowa systems (East Okoboji and West Okoboji) during fall 2015, 2016, and 2017 using mark-recapture techniques. Each fall, roughly 4000 stocked walleye were implanted with passive integrated transponder tags, stocked across both systems, and recaptured via boat electrofishing. Cormack-Jolly-Seber recapture models estimated walleye weekly apparent survival was negatively related to the weekly average proportion of walleye recovered from predator diets (β = −0.89; 95 % credibility interval = −1.74 to −0.03) and positively related to weekly average water temperatures (β = 2.62; 95 % credibility interval = 1.04–4.21). At an average fall water temperature (13.2 ℃), mean walleye apparent survival was 0.83 (95 % credibility interval = 0.75–0.91) when no walleye were recovered from predator diets and declined to 0.54 (95 % credibility interval = 0.28–0.84) when walleye comprised 60 % of predator diets. Between 41–97 % of stocked walleye were lost to apparent mortality from stocking through ice-up and survival was influenced by post-stocking predation rather than walleye body size or condition. Thus, strategies that minimize predation following stocking may result in the greatest improvements in walleye stocking success.

Evaluating the Role of Boat Electrofishing in Fish Monitoring of the Sacramento–San Joaquin Delta

The San Francisco Estuary is an incredibly diverse ecosystem with a mosaic of aquatic habitats inhabited by a number of economically, culturally, and ecologically important fish species. To monitor the temporal and spatial trends of this rich fish community, long-term fish monitoring programs within the estuary use a variety of gear types to capture fish species across life stages and habitats. However, concerns have been raised that current sampling gears may fail to detect certain species—or life stages—that inhabit areas that are not accessible by current gear types (e.g., riprap banks, shallow vegetated areas). Boat electrofishing is one sampling method that has been proposed to supplement current long-term fish monitoring in the upper estuary. In this study, we used fish catch data from past boat electrofishing studies, a long-term beach seine survey, and a couple of long-running trawl surveys to compare the relative probability of detecting various fishes across these sampling gears. Overall, we found that boat electrofishing led to notable improvements in the detection rates for many native and non-native fishes we examined. Boat electrofishing gear was better at detecting the majority of species in the spring (20 out of 38 species, 53%) and fall-winter (24 out of 34 species, 70%) sampling periods. Based on these findings, we recommend that resource managers consider the implementation of a long-term boat electrofishing survey to help them in their long-term conservation planning for fishes within the upper estuary.

Evaluating the Role of Boat Electrofishing in Fish Monitoring of the Sacramento–San Joaquin Delta

The San Francisco Estuary is an incredibly diverse ecosystem with a mosaic of aquatic habitats inhabited by a number of economically, culturally, and ecologically important fish species. To monitor the temporal and spatial trends of this rich fish community, long-term fish monitoring programs within the estuary use a variety of gear types to capture fish species across life stages and habitats. However, concerns have been raised that current sampling gears may fail to detect certain species—or life stages—that inhabit areas that are not accessible by current gear types (e.g., riprap banks, shallow vegetated areas). Boat electrofishing is one sampling method that has been proposed to supplement current long-term fish monitoring in the upper estuary. In this study, we used fish catch data from past boat electrofishing studies, a long-term beach seine survey, and a couple of long-running trawl surveys to compare the relative probability of detecting various fishes across these sampling gears. Overall, we found that boat electrofishing led to notable improvements in the detection rates for many native and non-native fishes we examined. Boat electrofishing gear was better at detecting the majority of species in the spring (20 out of 38 species, 53%) and fall-winter (24 out of 34 species, 70%) sampling periods. Based on these findings, we recommend that resource managers consider the implementation of a long-term boat electrofishing survey to help them in their long-term conservation planning for fishes within the upper estuary.

Operational Impacts of a Water Management Structure on the Surrounding Fish Assemblages in a Restored Backwater and a Large Floodplain River

Water management structures (WMS) are used to regulate water levels between large floodplain river backwaters and their adjacent river systems offering a balance between maintaining quality backwater habitat and providing benefits to the river systems. The design and operation of these WMS is dependent on unique management goals, and their impacts on the surrounding ecosystem are understudied. From 2016–2018 we quantified the response of the surrounding fish assemblages (i.e., backwater and river abundance and composition) to the WMS operation at the Emiquon Preserve, a 2723 ha restored floodplain lake located adjacent to the main channel of the Illinois River, U.S.A. Environmental conditions were recorded, and fish were collected using boat electrofishing on both sides of the WMS under three operational levels: closed and no flow, gravity flowing water, and mechanically pumping water to the river. Multivariate analyses determined that there was no difference in fish community composition within the Emiquon Preserve among operation levels. Within the river there were differences in community composition when the WMS was closed and mechanically pumping water. Environmental parameters varied seasonally and WMS operation level varied but indicated an increase in chlorophyll-a in the river when the WMS was mechanically pumping water, although the chlorophyll-a decreased within 200 m downstream of the WMS in the Illinois River. This study suggests that managed connections between restored backwater and habitats operated like this WMS have variable, spatially isolated impacts on fish communities despite supplying chlorophyll-a to large river ecosystems.

Fish assemblages of the St. Joseph River Watershed, Indiana: Effects of mainstem dams

AbstractWe tested for effects of two dams on fish assemblages in the St. Joseph River, Indiana. Fishes were collected by boat electrofisher twice annually, at 23 sites from 1998 to 2018. Fish collection data were aggregated into CPUE counts of species per 500 m, and CPUE were pooled across sites above and below the dams. We used multivariate analyses to test for spatial and temporal variation for assemblages above and below dams. Assemblages above and downstream of the dams differed significantly when examined by collection year. The effects (abundances of fish species) of the dams on fish assemblages were different at the South Bend dam from those at the Elkhart dam. Trajectories of temporal change in fish assemblages above and below dams were all gradual and directional. Temporal variation in fish abundance categorised into trophic traits (guilds) differed by location. We suggest that moderate to high stress from anthropogenic impacts on the St. Joseph River appears to result in high assemblage variation above and below dams. The St. Joseph River fish community appears to be unstable, likely from multiple anthropogenic impacts to water quality, habitat degradation and hydrologic alteration. We found that 25 of 33 hydrologic variables in four of five Indicators of Hydrological Alteration groups were significantly altered from 1931 to 2019. However, hydrology variation as potential disturbance events did not visually match observed temporal assemblage variation.

Freshwater fish functional and taxonomic diversity above and below Niagara Falls

The Niagara River, which connects two Great Lakes (Erie and Ontario) and forms a border between Canada and the United States, has experienced decades of abiotic and biotic disturbance as well as long-term restoration efforts. Given the iconic riverscape and importance as a binational fisheries resource, a biodiversity assessment of the mainstem Niagara River fish assemblage is overdue. Here, fish assemblage and habitat data from a standardized boat electrofishing program of the Niagara River were combined with species trait data related to substrate associations, diet preferences, reproductive strategies, and body size to quantify biodiversity patterns among river sections (sites above and below Niagara Falls), seasons (spring, summer, fall), and years (2015–2017). Sixty-five species were captured representing a variety of trait combinations. Significant differences in functional dispersion and divergence (i.e., functional diversity) were observed between river sections, seasons, and (or) years. The fish community captured in the lower river in spring 2015 had both the highest average functional dispersion (2.08 ± 0.32 SD) and divergence (0.88 ± 0.04 SD) compared to the other seasonal sampling efforts, but relatively few fishes were captured (n = 686). Although non-native fishes represented a small portion of the catch over the 3 years (8.6% of catch), the seasonal presence (spring and fall) of mostly introduced large-bodied salmonids expanded functional trait space in the lower river during these periods. The importance of rare species on functional diversity metrics suggests further insight on local species detection probabilities is needed to understand if differences in functional diversity reflect ecological patterns or are driven by sampling design.

Variation in Reproductive Investment among Ohio Reservoir Largemouth Bass Populations

AbstractReproductive investment, expressed in terms of fecundity and egg quality produced by individual female fish, varies among populations for many species, reflecting plasticity in life history strategies related to intraspecific density dependence or environmental variability. Fisheries scientists and managers have long sought to understand differences in Largemouth Bass Micropterus salmoides population dynamics, yet basic life history traits, such as variation in reproductive investment, remain largely unknown. We determined the fecundity–weight and ovary energy density–weight relationships (where fecundity indexes egg quantity and ovary energy density indexes egg quality) for Largemouth Bass populations from 19 Ohio reservoirs and examined factors that were correlated with population‐specific differences. We found that both relationships varied among reservoir populations, with some interannual variation in reservoirs sampled in multiple years. We then related fecundity and ovary energy density to (1) population characteristics, including population density (as indexed by standard shoreline boat electrofishing CPUE, fish/h) and growth (as indexed by the growth coefficient k from the von Bertalanffy growth function); and (2) reservoir characteristics, including reservoir size (as surface area) and productivity (as Secchi transparency depth). We found that populations with greater fecundity also exhibited greater ovary energy density, indicating that the quantity and quality of reproductive output were greater in some populations than in others. Populations with high reproductive investment were associated with low Largemouth Bass density, fast growth, large reservoir size, and high productivity (i.e., low Secchi transparency). The among‐population variation in reproductive investment provides evidence of density‐dependent control of fecundity and egg quality.

Validation of the model-predicted spawning area of grass carp Ctenopharyngodon idella in the Sandusky River

Spawning of grass carp, Ctenopharyngodon idella, in the Great Lakes basin was verified when eight fertilized eggs were collected in the Sandusky River, a tributary to Lake Erie, in 2015. Using a fluvial drift model (FluEgg) and simulation modeling, researchers predicted the fertilization location for those eggs was 3.8 ± 1 km (95% credible interval, CI) downstream of Ballville Dam. In June 2018, simultaneous collection of fertilized eggs and adults within the model-predicted spawning area provided the opportunity to verify the fertilization location. We used estimated developmental time (Dt) of eggs calculated from developmental stages, water temperature, and an equation that predicts Dt from cumulative thermal units experienced by developing eggs, in two analyses. First, we regressed Dt versus location of capture and solved that equation for developmental time of 0 hrs (Dt0) to estimate fertilization location. Second, we used Dt in the Fluvial Drift Simulator (FluEgg) to simulate 23 scenarios representative of drift conditions throughout the spawning event using the model-predicted spawning area and the site of Ballville Dam as potential spawning locations. Regression analysis placed the mean fertilization location 3.36 km (95% CI 2.27, 4.24) downstream of the site of Ballville Dam, within the model-predicted spawning area. Drift models demonstrated the model-predicted spawning area was best supported. Histograms of fertilization times overlapped with capture times by boat electrofishing of diploid adult grass carp in the model-predicted spawning area. This suite of analyses confirms the model-predicted spawning area and validates the methodology used to locate it.

Abundance, distribution, and habitat use of fishes in a large river (Danube, Austria): mobile, horizontal hydroacoustic surveys vs. a standard fishing method

Abstract We tested a novel approach for fish abundance and size estimates along a 3.6-km reach in the main stem of a free-flowing section of the Danube River east of Vienna. We deployed an adaptive resolution imaging sonar (ARIS) with horizontal beam orientation from a moving boat in order to assess spatial and temporal fish abundance distributions in different mesohabitats. To validate the results obtained from imaging sonar, hydroacoustic abundance and fish length estimates were compared with those received from boat electrofishing surveys conducted at the same time and place. Furthermore, fish occurrence was related to hydraulic conditions based on a three-dimensional hydrodynamic model in order to reveal patterns of habitat use. Hydroacoustic abundance expressed as catch per unit effort estimates deviated significantly from fish abundances assessed by boat electrofishing, but when comparing relative abundances both methods yielded a similar spatial and temporal pattern. Total fish length estimates obtained from the two methods did not differ significantly. The mobile application of the non-invasive ARIS technology offers the opportunity to quickly gain detailed information on fish abundance and position of individuals. This yields more specific information on temporal and spatial distribution patterns, habitat use and fish size distributions in large rivers.

Electrofishing Encounter Probability, Survival, and Dispersal of Stocked Age‐0 Muskellunge in Wisconsin Lakes

AbstractBoat electrofishing is often used to sample age‐0 Muskellunge Esox masquinongy for indexing recruitment or evaluating stocking success. However, electrofishing samples typically result in low CPUE, prompting concerns regarding whether catch rates reflect actual abundance or whether boat electrofishing is generally ineffective for capturing age‐0 Muskellunge (i.e., if fish are not being encountered by the gear). To address these concerns, we used radiotelemetry to evaluate the probability of encountering stocked age‐0 Muskellunge (230–350 mm TL) during standardized fall electrofishing surveys in three Wisconsin lakes. Our approach also allowed us to evaluate short‐term survival and dispersal from stocking locations. Despite limited dispersal (<2.5 km) from the stocking locations and relatively high short‐term survival (75–94%) of radio‐tagged fish, few age‐0 Muskellunge were located within the path of the electrofishing boat (7–30%). Furthermore, the probability of encounter by boat electrofishing varied by as much as 6.3 times among lakes. Differences in encounter probability among lakes appeared to be related to lake basin and habitat characteristics. Overlays of electrofishing sampling effort and fish locations revealed that traditional shoreline electrofishing may not be an effective way of estimating age‐0 Muskellunge CPUE. Modifications to electrofishing protocols, including increased effort in offshore areas and consideration of basin characteristics and habitat, may be needed to increase encounter probabilities and the utility of boat electrofishing for sampling age‐0 Muskellunge.

Diel patterns in spatial distribution of fish assemblages in lentic and lotic habitat in a regulated river

AbstractFish assemblages in large rivers are governed by spatio‐temporal changes in habitat conditions, which must be accounted for when designing effective monitoring programmes. Using boat electrofishing surveys, this study contrasts species richness, catch per unit effort (CPUE), total biomass, and spatial distribution of fish species in the Saint John River, New Brunswick, Canada, sampled during different diel periods (day and night) and macrohabitats (hydropower regulated river and its reservoir) in the vicinity of the Mactaquac (hydropower) Generating Station. Taxa richness, total CPUE, and total biomass were significantly higher during night surveys, resulting in marked differences in community composition between the two diel periods. Furthermore, the magnitude of diel differences in catch rate was more pronounced in lentic than in lotic macrohabitats. The required sampling effort (i.e., number of sites) to increase accuracy and precision of CPUE estimates varied widely between fish species, diel periods, and macrohabitats and ranged from 15 to 185 electrofishing sites. Determining a correction factor to contrast accuracy and precision of day‐ with night‐time surveys provide useful insights to improve the design of long‐term monitoring programmes for fish communities in large rivers. The study also shows the importance of multihabitat surveys to detect differences in the magnitude of diel changes in fish community metrics.

A Comparison of Grass Carp Population Characteristics Upstream and Downstream of Lock and Dam 19 of the Upper Mississippi River

Abstract Grass Carp Ctenopharyngodon idella have been intentionally stocked for aquatic vegetation control across the Midwestern United States for several decades. During the 1970s, escapement of Grass Carp into the Missouri River facilitated their naturalization into much of the Mississippi River basin, including the Upper Mississippi River. Lock and Dam 19 (LD19) in Keokuk, Iowa, is a high-head dam that represents a focal point for naturalized Grass Carp management where populations may differ between upstream and downstream pools as result of limited upstream migration, but potential differences between populations have yet to be evaluated to the best of our knowledge. The objective of this study was to compare the relative abundance, size structure, condition, growth, and recruitment variability of Grass Carp collected upstream and downstream of LD19. We sampled Grass Carp monthly (April–October) during 2014 and 2015 from four locations in the Des Moines River (downstream of LD19) and five locations throughout the Skunk, Iowa, and Cedar rivers (upstream of LD19) using boat electrofishing and trammel net sets. We captured 29 Grass Carp upstream of LD19 compared with 179 individuals captured downstream. Trammel nets only captured Grass Carp downstream of LD19; trammel net catch per unit effort upstream of LD19 was low and ranged from 0.0 to 8.0 fish/net lift (mean ± SE = 0.39 ± 0.13). Electrofishing catch per unit effort ranged from 0.0 to 22.7 fish/h (1.49 ± 0.30) and was higher downstream (2.42 ± 0.30) of LD19 than upstream (0.57 ± 0.07). Grass Carp downstream of LD19 tended to be smaller, younger, of lower body condition, had higher mortality rates, and were slower growing compared with those collected upstream and to populations documented in other systems. Understanding and monitoring adult Grass Carp population characteristics upstream and downstream of LD19 is necessary to determine how they may change in response to ongoing harvest efforts for invasive carps in these river reaches.

Time versus Space: Choice of Effort Metric Can Avoid Bias in Boat Electrofishing Catch per Unit Effort

AbstractWhile catch per unit effort (CPUE) is the most widely used metric for expressing and comparing boat electrofishing catch data, “effort” has been inconsistently defined. Boat electrofishing guidelines refer to both time‐ and distance‐based metrics, with little consensus about the appropriateness of one over the other. Catch rate metrics that use time‐based effort may potentially be biased by gear saturation due to handling time. We evaluated the potential for bias resulting from effort metric choice by comparing catch rates based on one temporal and two spatial effort metrics—time, shoreline length, and a GPS‐based areal measurement—using 3 years of data from 288 sampling occasions when all three metrics were recorded simultaneously. We used pairwise comparisons to isolate the effect of effort metric choice and fit six candidate models to each potential pair of CPUE metrics: a simple linear model, four models with separate slopes for survey variables (lake, season, night or day, and habitat), and an asymptotic model. The best‐fit model was asymptotic when the time‐based CPUE metric was compared with both space‐based metrics, and the linear model accounting for habitat was the best‐fit model for the comparison between both spatial methods. These results indicate that using a time‐based measure of effort resulted in hyperstable CPUE when fish densities were high due to gear saturation. By comparison, spatial measures of effort were robust to changes in fish density. Observed habitat‐based variation in the relationship between the two spatial metrics suggests that a CPUE measurement based on shoreline distance is adequate for assessing trends in abundance within waters or areas with homogenous habitat but not locations with contrasting conditions. We recommend the use of an areal‐based effort metric due to its robustness to gear saturation, comparability between waters, and potential for incorporating other variables that influence the performance of CPUE.

The fate of 0+ asp (Leuciscus aspius) after being stocked in a reservoir

Artificial enhancement of fish populations by stocking is widespread practice. Yet, very little is known about short-term dispersal, capture efficiency and the effect of fish size and habitat suitability. Asp (Leuciscus aspius Linnaeus, 1758) was chosen as a model species, because of its protection in the Svihov Reservoir and common stocking to increase predator fish abundance in many biomanipulated waters. 0+ fluorescent-marked asp were stocked in dam, middle and tributary sites of Svihov Reservoir and subsequently monitored weekly for three weeks intervals by boat electrofishing for two consecutive years. Despite similar numbers of asp stocked, the recapture was six-times lower in a year with low water level and high macrophyte density. All captured asp were identified as of hatchery origin. In the dam site most asp were recaptured in or close to the semi-closed bay with shallow water, where they were stocked. In the middle site asp spread from the unsuitable site of stocking in all directions and only very few individuals were recaptured. In the tributary site, asp dispersion was the most evident in 2017 in the direction towards the dam in the littoral zone opposite the bank that was the bank of stocking. In comparison the highest recapture was found at the site of stocking in 2018. The recaptured asp were of similar or larger size than the average stocked asp, which may suggest size-dependent mortality. The mortality of stocked asp may be affected by failure in foraging and antipredator behaviour. This research highlights the importance of post-release monitoring.

Borrowing external information to estimate angler size selectivity: model development and application to Murray cod

Estimating the size selectivity of fishery users and sampling methods can be difficult to achieve due to data limitations. However, these limitations can be moderated by borrowed information from other sources such as other systems, times, and species. Here we develop a model that integrates an externally sourced boat electrofishing length–vulnerability model with internally sourced boat electrofishing and angling catch data to estimate length-dependent vulnerability of fish to angling in a data-limited situation. We apply the model to Murray cod (Maccullochella peelii) as an example and show that angling for Murray cod selectively captures a narrow range of sizes that includes medium to large size fish. Although boat electrofishing also followed a similar pattern, the range of fish sizes vulnerable to capture was much broader, including a more uniform vulnerability of all size classes evaluated. Understanding the length selectivity to capture has key implications for effective determination of fisheries regulations, as well as interpreting monitoring data. Thus, we see this modelling approach as a good option when more informative data are not available to support the estimation process.

Variation in Bluegill Catch Rates and Total Length Distributions among Four Sampling Gears Used in Two Wisconsin Lakes Dominated by Small Fish

AbstractMany Bluegill Lepomis macrochirus populations are dominated by fish ≤125 mm total length (TL) that may be underrepresented when using standard sampling gears. To identify efficient sampling methods for these populations, we compared catch per unit effort (CPUE) and TL frequency distributions of Bluegill captured in cloverleaf traps, boat electrofishing, mini‐fyke nets, and beach seine hauls from two northern Wisconsin lakes supporting populations dominated by fish ≤125 mm TL. Mean Bluegill CPUE ranged from 41 (SE = 11) fish per cloverleaf trap lift to 16 (SE = 8) fish per beach seine haul. Cloverleaf traps generally captured smaller Bluegill relative to other gears and were the only gear to consistently capture Bluegill ≤80 mm TL. Conversely, boat electrofishing captured the widest TL range of Bluegill, and fish ≥80 mm TL composed a greater proportion of catch (37%) relative to other gears. With few exceptions, the effort required to detect 10% or 25% changes in Bluegill CPUE was >100 units of effort regardless of lake, sampling gear, or month. Furthermore, there was no consistency between lakes or months in terms of which sampling gear required the fewest number of samples to detect a 50% change in CPUE. Estimated units of effort needed to detect 10% or 25% changes in mean Bluegill TL were ≤16 for all sampling gears on the lake with consistently higher CPUE (i.e., more fish to measure per unit). In the lake with lower CPUE, cloverleaf traps consistently required less effort to detect changes in mean TL. We note that comparing sample size requirements among gears is not straightforward because gears are sampling differing segments of the Bluegill population. Our study emphasizes the importance of evaluating gear biases and sampling efficiency so that fisheries managers can develop suitable sampling protocols.

Host Usage and Evidence of Chestnut Lamprey Distribution in Selected Arkansas Streams

We documented distributional evidence of the parasitic fish Ichthyomyzon castaneus (Chestnut Lamprey) in selected Arkansas streams to provide information on host usage and selection of attachment sites. The species was at one point considered common in Arkansas streams, yet our sampling using boat electrofishing during late summer and fall collected Chestnut Lampreys in only 3 of the 12 streams for a total of just 8 individuals. We found evidence of Chestnut Lamprey parasitism in 7 of the 12 streams. Of the 2166 non-lamprey fishes collected, 11 individuals (0.5%) from 4 species bore evidence of Chestnut Lamprey parasitism. The most frequently parasitized host was the large-bodied, non-native Cyprinus carpio (Common Carp). There were no obvious patterns in the attachment/wound site location of parasitized fish. Further surveys of Arkansas streams are needed to evaluate trends in Chestnut Lamprey abundance and distribution.

A Comparison between Conventional Boat Electrofishing and the Electrified Dozer Trawl for Capturing Silver Carp in Tributaries of the Missouri River, Missouri

AbstractSilver Carp Hypophthalmichthys molitrix are elusive fish that can be difficult to capture with conventional management tools. New tools must be developed to help increase the capture of Silver Carp, thereby improving the understanding and management of the species. An electrified dozer trawl was developed in an attempt to increase the capture of Silver Carp while reducing the amount of sampling effort needed to successfully assess a population and inform management actions. We compared Silver Carp catch rates, sample run time, and Silver Carp length frequency distributions from the electrified dozer trawl with those from conventional boat electrofishing. Silver Carp capture was greater and sample time was shorter for the electrified dozer trawl compared to conventional boat electrofishing. Length frequency distributions were similar between gears. The electrified dozer trawl can shorten sample run times and potentially improve Silver Carp capture, thus facilitating management. Use of the electrified dozer trawl should be expanded beyond Missouri River tributaries to further understand the gear's potential for sampling Silver Carp in a diverse array of environments.