Electrofishing Equipment Research Articles

Feeding ecology of a stream fish assemblage in an Atlantic Forest remnant (Serra do Japi, SP, Brazil)

This study aimed to characterize the trophic structure of the fish assemblage in streams of the Serra Japi, an ecotonal area between the Atlantic Forest and inland forests of São Paulo State, Southeastern Brazil. Fish were collected with electrofishing equipment in 15 sites covering different regions, substrate types and riparian vegetation, distributed throughout the Caguaçú River, Caxambú, Piraí and Guapeva River micro-basins, during the rainy (January/February) and dry season (June) of 2007. The 589 specimens analyzed from 22 species, were assigned to different trophic groups, discriminated through a matrix of similarity, based on the food index (IAi). The results show the formation of seven groups with a predominance of insectivorous and omnivorous species, followed by detritivores, piscivores, omnivore-carnivores and herbivores, which consumed mostly items of autochthonous origin, where algae and young insects were dominant. Canonical correspondence analysis (CCA), correlating the biomass of trophic groups to environmental variables, showed that omnivores, insectivores and omnivore-carnivores displayed a wide distribution, while detritivores, herbivores and piscivores were restricted to specific locations, related to different physical and chemical variables as total nitrogen, conductivity and temperature. Despite the increase in total biomass at the most urbanized sites, the results indicate that the streams maintain a diverse community, suggesting that most of them are in preserved conditions.

Understanding Smith‐Root LR‐24 Equipment Specifications

AbstractThis study developed a graphic technique to assist electrofishing personnel in their understanding of the specifications and operational limitations of the Smith‐Root LR‐24 backpack electrofisher. No electrical measurements or complicated calculations were necessary to create this visual analysis; the technical information was simply taken from the advertised specifications for the LR‐24. The resulting graphic was empirically validated by means of comparative data obtained with the electrofisher adjusted to deliver its maximum output voltage, current, and power while it was wired to electrical loads of known resistance. In additional, the results from this study show how the power ratings of the LR‐24 are inherently dependent on the resistance of the electrical load and the duty cycle of the pulsed DC waveform. It was concluded that the area outlined on a four‐parameter graph adequately portrays the operational limits of the LR‐24. This graphic approach can be extended to other types and models of electrofishing equipment.

Trophic structure of a fish community along environmental gradients of a subtropical river (Paraitinga River, Upper Tietê River Basin, Brazil)

This research characterized the feeding ecology of the fish community of the upper-middle course of Paraitinga River, located within the Upper Tiete River Basin, a peculiar Atlantic Forest area, regarded as a hotspot for fish conservation. Considering the several anthropogenic modifications, knowledge of the trophic structure might contribute to a better understanding of the factors that maintain the present fish community. Fish were collected with electrofishing equipment at 16 sites with different riparian vegetation, including native forest, secondary forest, pasture, and Eucalyptus, during the dry and rainy season of 2004/2005. Results obtained for 15 species indicated a predominance of insectivores and herbivore-detritivores along the course and an increase of total biomass, specifically of the herbivores-detritivores at the pasture sites, which seemed to be mediated by specific habitat features, which included open canopy, high water speed, and deeper areas. Strategies of resource use indicated that 47% of total combination pairs showed high overlap, but competition seemed to be minimized through low co-occurrence, spatial segregation, and abundance of food resources. Niche width was broad for all species, with no significant differences occurring among sites, seasons, and upper and lower course. With regard to the ongoing modifications in riparian zone conditions in this area, the implications of these findings for regional biodiversity conservation are discussed.

Smallmouth Bass and Largemouth Bass Predation on Juvenile Chinook Salmon and Other Salmonids in the Lake Washington Basin

AbstractWe assessed the impact of predation by smallmouth bass Micropterus dolomieu and largemouth bass M. salmoides on juveniles of federally listed Chinook salmon Oncorhynchus tshawytscha and other anadromous salmonid populations in the Lake Washington system. Bass were collected with boat electrofishing equipment in the south end of Lake Washington (February–June) and the Lake Washington Ship Canal (LWSC; April–July), a narrow waterway that smolts must migrate through to reach the marine environment. Genetic analysis was used to identify ingested salmonids to obtain a more precise species‐specific consumption estimate. Overall, we examined the stomachs of 783 smallmouth bass and 310 largemouth bass greater than 100 mm fork length (FL). Rates of predation on salmonids in the south end of Lake Washington were generally low for both black bass species. In the LWSC, juvenile salmonids made up a substantial part of bass diets; consumption of salmonids was lower for largemouth bass than for smallmouth bass. Smallmouth bass predation on juvenile salmonids was greatest in June, when salmonids made up approximately 50% of their diet. In the LWSC, overall black bass consumption of salmonids was approximately 36,000 (bioenergetics model) to 46,000 (meal turnover consumption model) juveniles, of which about one‐third was juvenile Chinook salmon, one‐third was coho salmon O. kisutch, and one‐third was sockeye salmon O. nerka. We estimated that about 2,460,000 juvenile Chinook salmon (hatchery and wild sources combined) were produced in the Lake Washington basin in 1999; thus, the mortality estimates in the LWSC range from 0.5% (bioenergetics) to 0.6% (meal turnover). Black bass prey mostly on subyearlings of each salmonid species. The vulnerability of subyearlings to predation can be attributed to their relatively small size; their tendency to migrate when water temperatures exceed 15°C, coinciding with greater black bass activity; and their use of nearshore areas, where overlap with black bass is greatest. We conclude that under current conditions, predation by smallmouth bass and largemouth bass has a minor impact on Chinook salmon and other salmonid populations in the Lake Washington system.

Refining Boat Electrofishing Equipment to Improve Consistency and Reduce Harm to Fish

AbstractA major concern with electrofishing is the standardization of sampling equipment and methods, particularly when collections are used to monitor spatial and temporal changes in fish communities. Standardization can not only ensure that stock assessment is consistent—that is, the data collected over time and space have equal meaning and are not influenced by differences in gear or gear application—but also reduce injury by constraining power to ranges that are likely to immobilize fish but unlikely to harm them. Standardization of electrofishing equipment requires adjusting power output to keep constant the amount of power transferred to fish in diverse water conditions. In this study, the power level thresholds required to immobilize and injure fish under controlled laboratory conditions were identified for various size–species combinations and applied to establish power minima and maxima suitable for successful and safe boat electrofishing. The target settings identified allowed survival of 99.4% of the fish collected and held for 2–3 h during field trials; all the mortalities were small fish (≤53 mm long). The standardization procedure described herein may be adapted to single boats or fleets and can promote consistency in electrofishing, although it does not completely avoid harm to fish. Because electrofishing is an active capture method applied to changing microenvironments, complete standardization and total avoidance of harm to individual fish are not feasible with present technology, but standardization of controllable variables is advisable.

Golden Loach (Sabanejewia Aurata (De Filippi, 1865)). A New Freshwater Fish Species in Lithuania

Only two loach species – Cobitis taenia and Misgurnus fossilis – have been known until in Lithuania. On 21 August, 2002 a new species of another loach genus, golden loach (Sabanejewia Aurata), was discovered. All these fish individuals were caught in the Venta River basin, one of them being caught in the Venta River near the Kuodžiai mill and three others – in the Serksnė River mouth. The fish were caught with electrofishing equipment and a fish dredge. The golden loach range covers fresh waters of the Baltic, Aegean, Black, Azov, Caspian and Aral Sea basins. Closest to Lithuania this fish has been first recorded quite recently in Poland, the Odra River basin. In 1994, a new subspecies of the Baltic Sea basin (Witkowski 1994) was identified.

Impact of introduced trout on Nesameletus mayfly populations measured using electrofishing

Despite the widespread introduction of salmonid fishes for sports fisheries their effects on recipient invertebrate communities are not well understood. This lack of knowledge is associated with the methodological difficulties involved in assessing the effects of predatory fish on stream invertebrate populations. A sampling technique, involving the use of backpack electrofishing equipment, was used to compare the abundance of Nesameletus mayflies in 15 streams varying in the presence of introduced brown trout (Salmo trutta) and native Canterbury galaxias (Galaxias vulgaris). Nesameletus were induced to drift into a downstream net by applying electric current to 2m 2 of stream bed using a small (12 cm diameter) anode. Density estimates for Nesameletus from electrofishing were on average five times higher than those obtained from Surber sampling. Fishless streams and streams with only Canterbury galaxias contained a biomass and density of Nesameletus that were two to three orders of magnitude higher than streams with only brown trout. When Canterbury galaxias and trout were both present, however, densities of Nesameletus were intermediate to those found in trout versus troutless streams. This could be because 'trout only' streams contained larger trout which were more effective predators. Streams with trout were wider, but were otherwise not consistently different from those without trout so comparisons were unlikely to be confounded by physical conditions. The average size of nymphs in fishless streams was significantly smaller because a new generation of nymphs had hatched in fishless streams, but was absent from streams containing fish. The effects of the introduced fish on Nesameletus populations indicate that troutless streams are important habitats for maintaining regional Nesameletus spp. populations and that further range expansions of brown trout could decrease populations of vulnerable invertebrates.

Assessment of Outputs from Smith-Root Model-5.0 GPP and Model-7.5 GPP Electrofishers

Abstract We evaluated the outputs from eight Smith-Root electrofishers (two factory-rigged model-5.0 GPP boats, four biologist-rigged model-5.0 GPP boats, and two biologist-rigged model-7.5 GPP boats), using an oscilloscope to determine the actual waveforms (voltage as a function of time), current, and power produced for various settings. Differences were found in average power outputs among the six model-5.0 GPP electrofishing boats. In terms of average power output, biologist-rigged electrofishing boats using generators and control boxes purchased from Smith-Root were as or more effective than those rigged by Smith-Root. However, factory-rigged boats generally contained additional safety features that should be considered when purchasing electrofishing equipment. Outputs were similar between the two model-7.5 GPP boats. We were unable, with information obtained solely from the control boxes, to calculate power output produced by the Smith-Root electrofishers. Thus, additional meters (e.g., a voltage met...

Sampling stream invertebrates using electroshocking techniques: implications for basic and applied research

We present a new technique using electrofishing equipment to collect and quantitatively sample stream invertebrates. We used an electrofishing machine with a small anode to produce a localized field of pulsed direct current to induce invertebrate drift. We quickly obtained large numbers of live invertebrates for experiments by passing the anode over the stream bottom upstream of sampling nets. We compared the results of five techniques: (i) electroshocking inside a modified Hess sampler, (ii) repeated electroshocking over a large area to estimate population size by depletion, (iii) traditional Surber, (iv) Hess, and (v) individual stone sampling. Electroshocking techniques provided estimates of invertebrate density comparable with those of traditional sampling techniques. The electroshocking depletion method that sampled a large area provided higher measures of Ephemeroptera, Plecoptera, and Trichoptera richness. Hess and area-restricted electrobug methods had similar density and diversity estimates, whereas the Surber sampler provided low density estimates, especially for mobile taxa. Density estimates from individual stones were inflated, were biased for mayflies, and had low richness. Samples taken with the electroshocking method were processed 40% faster because these samples contained little detritus. Electroshocking techniques can provide accurate estimates of population size and diversity, minimize disturbance to benthic habitats, and reduce processing time.

Vulnerability of Spotted Bass to Angling in Kansas Streams

ABSTRACT In 1996 and 1998, standardized angling was conducted on four streams to determine the vulnerability of stock-length (≥ 180 mm) spotted bass (Micropterus puntulatus) to angling. Block nets were used to prevent movement of fish into or out of the reach. Two anglers fished the entire reach from the bank. After angling was completed, spotted bass were sampled using pulsed-DC backpack electrofishing equipment. A three-pass depletion method was used to estimate density. Population estimates varied from three to five stock-length spotted bass per 100 m of stream reach, and density varied from 21 to 63 spotted bass/ha. Mean angler catch per effort was 0.39 fish/h and potential harvest was 5.1 fish/ha. Percent of the spotted bass population that was captured by angling varied from 0% to 26%.

Food Habits of Walleye in Shadehill Reservoir, South Dakota

ABSTRACT The growth rate of walleye (Stizostedion vitreum) in Shadehill Reservoir, a 1,900-ha impoundment in Northwestern South Dakota, is much slower than the statewide average. We investigated the food habits of walleye in Shadehill Reservoir from 1994 to 1995 to determine if the slow growth is prey-related. Walleye were collected at night using electrofishing equipment and experimental gill nets. Of the 201 stomachs examined, 114 contained food. We calculated the relative importance (RI) index to evaluate the contribution of each prey item to the diet. Due to a relatively small sample size and inherent gear biases, data from all seasons were combined and analyzed by length group. The RI analysis indicated that Daphnia spp. was the most important prey for sub-stock length (<25 cm total length) walleye. White bass (Morone chrysops) became increasingly important for longer walleye and was the most important prey for quality- to preferred-length walleyes (38–50 cm TL). Aquatic dipteran larvae were the second most important prey in the diets of quality- to preferred-length walleye, which may indicate limited prey fishes for walleye in Shadehill Reservoir.

Improving Electrofishing Catch Consistency by Standardizing Power

Abstract The electrical output of electrofishing equipment is commonly standardized by using either constant voltage or constant amperage, However, simplified circuit and wave theories of electricity suggest that standardization of power (wattage) available for transfer from water to fish may be critical for effective standardization of electrofishing. Electrofishing with standardized power ensures that constant power is transferable to fish regardless of water conditions. The in situ performance of standardized power output is poorly known. We used data collected by the interagency Long Term Resource Monitoring Program (LTRMP) in the upper Mississippi River system to assess the effectiveness of standardizing power output. The data consisted of 278 electrofishing collections, comprising 9,282 fishes in eight species groups, obtained during 1990 from main channel border, backwater, and tailwater aquatic areas in four reaches of the upper Mississippi River and one reach of the Illinois River. Variation in p...

New Technique for Sampling Sea Lamprey Larvae in Deepwater Habitats

We describe an effective device for sampling for the larvae of sea lampreys Petromyzon marinus in waters too deep to wade and sample with backpack electrofishing equipment (> 1 m). The sampler uses electricity to stimulate emergence of larvae from the substrate and a pump to move them to the surface for collection. Capture efficiency was negatively related to larval length, but it seems possible to correct population density estimates to account for this factor if length data are collected from the catch.

Estimating population densities of salmonids in deep water in streams

Densities of salmon, trout and grayling were assessed in Scottish streams by systematic counting by underwater observers, where the water was greater than 1 m deep, and by using electrofishing equipment in adjacent shallower areas. Tests of the efficiencies of the two methods are described. Applications have included the estimation of production of trout, grayling and young salmon at a site on the River Tay and predicting the salmon smolt run of the River Tilt, and these applications are briefly described. The most suitable period for visual counting was summer, as at water temperatures of less than 15° C fish were hiding among stones in the stream bed. Wet weather hampered both electrofishing and visual counting.

Standing Crops of Brook Trout Concurrent with Removal of Rainbow Trout from Selected Streams in Great Smoky Mountains National Park

Abstract Stream surveys since the 1930's have shown a decline in the distribution of native brook trout (Salvelinus fontinalis) in Great Smoky Mountains National Park. Exotic rainbow trout (Salmo gairdneri) have been implicated as the major reason for the decline. Assuming that this hypothesis is correct, attempts were made to eradicate exotic trout from selected streams from 1976 to 1979 using backpack electrofishing equipment. Because this was the only sampling method allowed to capture fish, expenditures of field time were analyzed. Based upon the 4 years of work, an average of 0.68 man-days was required to electrofish each 100 m of stream section three times. Population estimates using the Zippin method were found to be low. Re-sampling of one stream during 1978 showed that the brook trout population was underestimated on the first sample by about 25%. Although rainbow trout were not eradicated from any study stream, major reductions in their numbers were observed. Brook trout standing crops increased...

Nonmetallic Electrofishing Booms and Accessory Tackle

Abstract The original strength and flexibility of nonmetallic (nonconducting) electrofishing booms were maintained by building special tackle from which to hang the electrodes and to suspend the booms above the water. The booms and tackle functioned well in field operations, and since the booms are nonconducting, they reduce the potential hazards associated with electrofishing equipment. Epoxy resin poles filled with poly-urethane foam were used instead of dimensional lumber, wooden dowels, hollow fiber glass poles, or aluminum tubing wrapped in fiber glass.