Day Versus Night Electrofishing Catches from Near-Shore Waters of the Ohio and Muskingum Rivers1 RANDALL E. SANDERS, Division of Water Quality Planning and Assessment, State of Ohio Environmental Protection Agency, 1685 Westbelt Drive, Columbus, OH 43228 ABSTRACT. Day and night electrofishing catches were compared for sampling effectiveness and diel movements offish to and from near-shore waters of the Ohio and Muskingum rivers. Standardized methods were used to collect same-day paired samples by sampling during the day, displacing the catch, and resampling after twilight. Night catches contained significantly higher numbers of species, individuals (excluding Dorosoma cepedianum), weight, and biological index scores (Modified Index of Well-Being [Mlwb] and Index of Biotic Integrity [IBI]). Night versus day paired samples in the Ohio and Muskingum rivers showed, respectively, mean increases of 7.6 and 4.6 species, 229 and 417 fish per km (excluding D. cepedianum), 18.2 and 30.4 kg/km, 2.3 and 1.5 Mlwb units, and 10.8 and 8.7 IBI units. Total night catches yielded, respectively, 43% and 15% more taxa, 62% and 160% greater numbers (excluding!), cepedianum), and 50% and 70% more weight than total day catches. Catch differences were primarily attributed to diel movements from off-shore to near-shore waters during the evening-twilight period. Taxa which increased the most at night in the Ohio River were: Alosa chrysochloris, Notropis wicklijfi, Ictiobus bubalus, Moxostoma anisurum, M. duquesnei, Ictalurus punctatus, Morone saxatilis x M. chrysops, Ambloplites rupestris, Stizostedion canadense, and Aplodinotus grunniens; and in the Muskingum River: Ictiobus bubalus, Moxostoma anisurum, and Morone chrysops. Standardized night electrofishing is an effective sampling technique for many mainstem species and provides a better, more complete biological assessment than day electrofishing. Therefore, it should be incorporated into long-term monitoring programs for these large, deep rivers. The findings of this study may also be applicable to other large, deep bodies of water elsewhere. OHIO J. SCI. 92 (3): 51-59, 1992 INTRODUCTION the evening-twilight period with movement from deeper Day versus night electrofishing studies have shown off-shore waters (Sanders and Yoder 1989). The difference night sampling, particularly in large bodies of water, can was not surprising, given the results reported in earlier yield more species, greater numbers, and larger individuals studies. However, such studies have primarily compared than day sampling because of a variety of reasons including: catches of sport species (i.e., Micropterus spp. and Lepomis diel movements, reduced gear avoidance, behavioral macrochirus) and have been conducted in lakes and changes, and increased visibility resulting from calmer reservoirs for management purposes. Except for a report waters (Loeb 1957, Witt and Campbell 1959, Sanderson of a similar investigation on the Ohio River (Geo-Marine I960, Frankenberger I960, Kirkland 1962, Baumann and 1986), few studies have been conducted in large, deep, Kitchell 1974, Sonski 1982, Gilliland 1985, Graham 1986, navigable rivers and have compared catches of all species Geo-Marine 1986, Paragamian 1989). Night sampling, for the purpose of biological assessment or diel movements however, can also produce undue fatigue, possible safety of nongame species. risks, or require overtime (Graham 1986), and is preferably The objectives of the present study were to answer the avoided if satisfactory results can be obtained through day following questions about day versus night electrofishing sampling. and diel movements in the Ohio and Muskingum rivers: Day electrofishing has been effectively used by Ohio Environmental Protection Agency (OEPA) personnel to 1. Does night sampling consistently catch more species, monitor and assess shallow (<3 m) inland rivers and individuals, and weight than day sampling? streams. Day catches from near-shore waters of the larger, 2. Do night catches provide a different biological deeper Ohio and Muskingum rivers, however, have been assessment than day catches? disappointing and are characterized by lower than expected 3. Do fish consistently move to shallow near-shore values for species richness, catch per unit effort (CPUE) for waters from deeper off-shore waters during the most species, and two biological indices (Modified Index evening-twilight period? If so, which species move of Well-Being [Mlwb] and Index of Biotic Integrity [IBI]). the most? The need for the present study was identified on 26 September 1986 when day and night electrofishing results Study Area from the Ohio River suggested that the composition of The study area was located in the Western Allegheny near-shore fish assemblages had markedly changed during Plateau and Interior Plateau ecoregions (Omernik 1987) and spanned a total distance of 760 river kilometers of the Ohio and Muskingum rivers (Fig. 1). Samples were 'Manuscript received 26 December 1991 and in revised form 9 March collected at six sites on the Muskingum and seven sites on 1992 (#91-26). the Ohio. Sites were 430-650 m long and contained a 52 DAY VERSUS NIGHT ELECTROFISHING VOL. 92 direction. Visual observations were also made on the relative effectiveness of the gear and netters (primary and assist). Turbidity levels were determined using a secchi disk. The Mlwb and IBI, two indices which measure environmental disturbances (higher scores usually reflect less impairment), were used to quantify day and night catches for the purpose of biological assessment. The Mlwb (modified version of the Index of Well-Being [Gammon 1976]) is a measure of the fish community based on a IND. calculation using relative number, biomass, and the Shannon Diversity Index (based on numbers and weight) from which highly tolerant and exotic fishes are removed from numbers and biomass calculations. The IBI (first introduced by Karr [1981]) consists of 12 metrics which assess fish assemblages based on species richness and composition, trophic composition, abundance, and health. The boat method IBI KENTUCKY metrics and scoring of the OEPA were used in the present study as an interim assessment tool until specific modifications FIGURE 1. Map of the Ohio and Muskingum rivers showing sampling sites for large, navigable rivers are developed. (black circles), paired sample number(s), upstream and downstream Statistical significance in the present study was set at river kilometers (RK), and dam locations (black rectangles). P <0.05 and determined only for differences between paired samples (Wilcoxon signed-ranks test) and turbidity scatter plots (simple curve fit). variety of habitats including narrow, steep-sloped margins with rocky or hardpan substrates and wide, gentle-sloped Study Design Considerations margins with silt, sand, or gravel substrates. A general Captured fish were released in good physical condition description of the Ohio River has been reported by immediately after data collection >100 m from the site Pearson and Krumholz (1984). (release locations included the same shore, opposite shore, and middle of the river). The mean time between MATERIALS AND METHODS release and the beginning of a night sample was 6.8 h Standardized field, laboratory, and data processing (range 3.5-11.0 h). It is unknown how many of the methods and procedures were used in this study (OEPA previously captured fish may have returned to the sampling 1987, 1989). Field collections were made using OEPA's sites prior to night sampling or what affect the disruption boat method between 19 July and 27 September 1988. A of local territories might have had on night catches. total of 18 same-day paired samples (Fig. 1) were collected by sampling first during the day (1115-1749 h), displacing RESULTS the catch, and resampling no sooner than 40 min after Throughout the survey, the total composite catch (day sunset (2012-0037 h). Multiple samples were collected and night) combined from both rivers weighed 1038.4 kg from three Marietta, OH, sites at monthly intervals. and consisted of 17,495 fish comprised of 59 species and Cumulative shoreline distances of 5.9 and 4.1 km, three hybrids (Table 1). The total composite catch from the respectively, in the Ohio and Muskingum rivers were Ohio River weighed 547.6 kg and consisted of 10,337 fish electrofished during the day and resampled at night. comprised of 48 species and two hybrids. The total Samples were collected using a 4.9 m flat-bottom composite catch from the Muskingum River weighed aluminum boat equipped with a straight electrode 490.8 kg and consisted of 7,158 fish comprised of 42 configuration consisting of four anodes suspended 2.6 m species and one hybrid. in front of the bow on a retractable boom, and four cathodes suspended from the bow. Smith-Root Type Species Richness and Frequency of Occurrence VI-A and GPP-3.5 electrofishers and 3500-watt gasoline Despite thorough day sampling and the displacement generators were used to produce pulsed direct current. of catches, the numbers of species collected in night Pulse width was set at 60 or 120 pulses per second and samples were significantly greater than all corresponding voltage was varied between 500-1000 VDC to produce an day samples from both rivers (Fig. 2a). Night samples output of 8-9 amperes. Two pairs of 75-watt floodlamps showed mean increases of 7.6 species (range 1 -12) in the (powered by a separate gasoline generator) mounted on Ohio River and 4.6 species (1 - 9) in the Muskingum River. the bow railing and six-volt headlamps provided light for Night electrofishing in the Ohio River yielded all 50 taxa night collections. The boat was operated by the same collected, while only 35 taxa were captured during the day individual during all samples and the same electrofishing (Table 1). Thirty-four of the 50 total taxa were captured gear and principal netter were used for each paired more frequently at night (15 exclusively), five taxa more sample. Sites were fished consistently and time fished often during the day, and 11 taxa equally during day and averaged 40.5 and 45.7 min, respectively, for day and night night samples.