Prairie Naturalist A.E. Gebhard, C.W. Goble, and C.M. Longhenry 2021 53:16–26 16 2021 PRAIRIE NATURALIST 53:16–26 Sampling Efficacy of Channel Catfish Using Tandem Hoop Nets and Trotlines Amy E. Gebhard1*, Cameron W. Goble2, and Christopher M. Longhenry1 Abstract - Channel Catfish (Ictalurus punctatus) is a popular species for anglers to target along the Missouri River system in South Dakota. Even though anglers target Channel Catfish, sampling this species along the Missouri River system in South Dakota has not been a management priority. One of the main reasons for this is a lack of standardized sampling protocols. This study was conducted to determine the relative effectiveness and efficiency of tandem hoop nets and trotlines for sampling Channel Catfish in a flashy, turbid tributary of the Missouri River in South Dakota. Both sampling gears were evaluated for 24-hour sets in June, July, and August 2019 at three sites on the White River, South Dakota. Catch per personnel hour of ef fort (CPPHE) for tandem hoop nets was over 17 times greater than trotlines during this study (W = 79, n = 18, P < 0.01). Tandem hoop nets also provided a much wider range of fish lengths than trotlines (65–644 mm vs. 171–631 mm respectively). No monthly differences were observed in catch rates or fish lengths throughout the three-month timeframe of the study. These results suggest that tandem hoop nets are an effective and efficient gear during summer months for standardized sampling of Channel Catfish in flashy , turbid Great Plains rivers. Introduction Catfish (family Ictaluridae) are one of the most sought-after groups of freshwater fishes in the United States of America with >6 million anglers targeting them annually (USFWS 2016). While catfish are highly sought after overall, there are regional differences in their popularity among anglers. In a 1997–1998 survey of North American fisheries resource agencies, Michaletz and Dillard (1999) found that the popularity of catfish was centered primarily in southern and midwestern United States. South Dakota was not included in the midwestern states that claimed catfish have high or even medium importance to anglers at a statewide level; however, there are areas within the state where catfish are highly popular among anglers. For example, catfish are the third most targeted group of fish for anglers along the Missouri River and its larger tributaries (Longmire 2019). Despite their national (and local) popularity, Ictalurus punctatus Rafinesque (Channel Catfish) are typically not sampled for management purposes in many lotic systems (e.g., the Missouri River system). Like many riverine species, Channel Catfish often use a wide variety of habitats (e.g., main-stem, tributaries, backwaters, reservoirs) throughout their lives. Pracheil et al. (2009) stressed that tributaries are an integral component of a riverine network. They provide complementary habitats that may regulate populations and enhance biodiversity in the large main-stem waters. Similarly, a multi-year study of Channel Catfish in the Missouri and Platte Rivers in Nebraska found that Channel Catfish regularly moved between rivers (Spurgeon 2016, Spurgeon et al. 2018). Their findings suggest that tributaries can contribute a significant number of individuals to river-network metapopulations and emphasize that connectivity and movement between a main-stem river and its tributaries are critical for Channel Catfish. 1South Dakota Department of Game, Fish and Parks, Chamberlain Regional Office, 1550 E. King Avenue, Chamberlain, South Dakota 57325, USA. 2South Dakota Department of Game, Fish and Parks, Ft. Pierre District Office, 20641 SD Highway 1806, Ft. Pierre, South Dakota 57532, USA. *Corresponding author: Amy.Gebhard@state.sd.us. Manuscript Editor: Keith Koupal Prairie Naturalist A.E. Gebhard, C.W. Goble, and C.M. Longhenry 2021 53:16–26 17 The Missouri River in South Dakota is broken up into four main-stem reservoirs: Lake Oahe, Lake Sharpe, Lake Francis Case, and Lewis and Clark Lake. Channel Catfish, while not being specifically targeted, are collected during annual standardized fish community gillnet surveys conducted in each reservoir. Data from these surveys suggest that Channel Catfish abundance may be declining in the Missouri River system in South Dakota (i.e., three out of four reservoirs show a negative trend in gillnet catches over the last 20 years; J. Lott and co-workers, South Dakota Game, Fish, and Parks, 2019 unpubl. data). While standardized survey data is available for the main-stem reservoirs, there is a lack of consistent and standardized fish population data collection for most tributaries. Because of this, little is known about Channel Catfish populations in the tributaries, and fisheries managers concerned with declining catches might be missing important data on potential changes in source habitats (e.g., Spurgeon 2016). However, gill net surveys would not be feasible in most of South Dakota’s Missouri River tributaries due to shifting sediment, floating and submerged debris, and current. Common sampling issues for assessing Channel Catfish include low catches and biased age and size distributions (Arterburn and Berry 2002, Long et al. 2017, Michaletz and Sullivan 2002, Vokoun and Rabeni 2001). A literature review on catfishes by Bodine et al. (2013) evaluated sampling efficiencies, precision, and accuracy of sampling gears and determined that baited tandem hoop nets were superior to gill nets, slat-traps, low or high frequency electrofishing, single un-baited hoop nets, and hook and line for sampling Channel Catfish in lotic systems. However, data collected during standard trotline sampling from Scaphirhynchus platorynchus Rafinesque (Shovelnose Sturgeon) in Lewis and Clark Lake during the spring of 2019 yielded 0.2 Channel Catfish per hook-set (Amy E. Gebhard and Christopher M. Longhenry, South Dakota Game, Fish, and Parks, 2019 unpubl. data). This catch per unit effort (CPUE) was 26.5 times greater than the mean trotline CPUE (0.0092 fish per hook-set) reported by Steffensen et al. (2011) and Steffensen et al. (2013) from sampling conducted in the channelized Missouri River. Higher than expected trotline CPUE of Channel Catfish bycatch in Lewis and Clark Lake, the la ck of tributary surveys, and negative trends in Channel Catfish data on three of the four Missouri River reservoirs provided the impetus for conducting an evaluation of gear efficiency to help establish a standardized sampling protocol for South Dakota’s flashy turbid rivers. Therefore, the objectives of this study were to: (1) determine if catch per personnel hour effort (CPPHE), length distribution, and age frequency distributions differ between tandem hoop nets and trotlines and (2) determine if there are gear specific differences in standard population indices (i.e., CPPHE , CPUE, and length distributions) across t he temporal scale. Methods Study Area The White River is the largest tributary in the portion of the Missouri River between Big Bend Dam and Ft. Randall Dam. It flows roughly ~930 km from the headwaters near the town of Harrison in northwestern Nebraska before discharging into Lake Francis Case Reservoir just south of Chamberlain, South Dakota. The White River was selected as the site for this study due to its proximity to the Chamberlain fisheries office, popularity as a catfish angling location, and knowledge that other species [e.g., Polyodon spathula Walbaum (Paddlefish)] leave the reservoir and inhabit the river on a seasonal basis (Pierce et al. 2011). The White River has a sandy shifting bottom typical of many Missouri River tributaries in central South Dakota and gets its name from the milky appearance caused by Prairie Naturalist A.E. Gebhard, C.W. Goble, and C.M. Longhenry 2021 53:16–26 18 a high sediment load. From 1972 to 2019, suspended sediment concentrations ranged from 3,339 to 8,728 milligrams per liter and average discharge ranged from 180.2 to 3,149 cubic feet per second (USGS 2021). Fish Sampling Our sampling was conducted monthly during June, July, and August 2019 using a fixedsite/ access-point survey design (Noble et al. 2007; Fig. 1). We placed 5 tandem hoop nets (THN) and 5 trotlines at each of the 3 sample sites (1–2 miles stretch of the river; Fig. 1). We randomly selected the downstream gear type (i.e., trotline or THN), and all other gear sets alternated throughout each site. Prior to each gear deployment, we made sure dissolved oxygen was >5 ppm near the bottom at each set location to reduce fatalities. A three-person crew was used throughout the duration of the study to set, bait, and work up gears. The total sample size per gear per month was 15 trotlines and 15 tandem hoop nets. However, in July, one of each gear type was buried in the sediment and lost, so only 14 of each gear type was reported for that month. Our tandem hoop net configuration was as follows: one 35-mm bar mesh hoop net set inline between two 21-mm bar mesh hoop nets with a 1-m rope bridle separating each hoop net in the series (Fig. 2). Each individual hoop net had four 0.5-m diameter hoops, one throat, and an overall length of 1.6 meters. We baited tandem hoop nets with one 0.45 kg nylon mesh sack of waste cheese per hoop net (Flammang and Schultz 2007, Michaletz and Sullivan 2002). We placed tandem hoop nets parallel to the bank near complex habitats (e.g., woody debris and rooted vegetation), thalweg, and cut banks (Arterburn and Berry 2002, Dickinson et al. 2018, Vokoun and Rabeni 2001), and fished them for approximately 24 hou rs. Our trotlines contained 20, 3/0 circle hooks baited with night crawlers on a 32-m mainline (Welker and Drobish 2012). We placed trotlines parallel to the bank near complex habitats (e.g., woody debris and rooted vegetation), thalweg, and cut banks (Arterburn and Berry 2002, Dickinson et al. 2018, Vokoun and Rabeni 2001) and fished them for approxi- Figure 1. Map showing the three sampling locations along the lower end of the White River, South Dakota. Prairie Naturalist A.E. Gebhard, C.W. Goble, and C.M. Longhenry 2021 53:16–26 19 mately 24 hours. A 4.5-kg navy anchor was attached to the upstream end while a 2.25–4.5 kg window sash weight was attached to the downstream end of the trotline. When we retrieved the gear, all Channel Catfish were counted, measured for total length (mm) and weighed (g). Channel Catfish were considered caught even if an individual fell out of the gear onto the boat deck. We removed otoliths from 10 individuals per 25-mm length bin at each site over the 3 months for each gear type following methods described by Harty (2017). We removed and processed lapilli otolith following the methods of Buckmeier et al. (2002). Two individuals independently aged the otoliths and a third individual was used to settle aging disagreements. Total personnel time required per set (i.e., baiting, setting, pulling, and removing fish but not fish work up time) for each THN and trotline were recorded to the nearest sec (Sullivan and Gale 1999). We later used this data to determine Channel Catfish CPPHE of each gear type. CPPHE equation: CPPHE = F / (T • C) where F is the number of Channel Catfish caught for one gear set, T is the time it took personnel to bait, set, pull, and empty one gear set (time in hours), and C is how many personnel it took to run that gear. Analysis Due to non-normality of the data, all analyses were performed with non-parametric tests. For our first objective, we conducted a Mann Whitney U test to test for a significant difference of CPPHE between gear types. The study design required CPPHE for each gear to be calculated as the mean of monthly site means. We used Kolmogorov-Smirnov (KS) tests Figure 2. Tandem hoop net configuration. Photo taken by Amy Gebhard. Prairie Naturalist A.E. Gebhard, C.W. Goble, and C.M. Longhenry 2021 53:16–26 20 to determine if there were significant differences in length distribution and age frequency distribution between gear types. For the second objective, we analyzed the data to determine if temporal differences occur between standard catch metrics (i.e., CPUE [gear-specific], CPPHE [gear-specific], and length distribution). Comparisons between monthly differences for CPUE, CPPHE, and mean length within gear types were performed with Kruskal-Wallis tests. All our analyses were conducted using Program R version 3.5.1 (R Core Team 2018) with an α level of 0.05. Results A total of 932 Channel Catfish were collected during this study. Tandem hoop nets (n = 887) caught more Channel Catfish than trotlines (n = 45; Table 1). Bycatch of non-target species during this study was low with Channel Catfish comprising ~ 98% of the trotline and THN catches. Aplodinotus grunniens Rafineque (Freshwater Drum) were the second most commonly captured species (~ 1%; trotline n = 1, THN n = 9) followed by Cyprinus carpio Smith (Common Carp) (~ 0.4%; THN n = 4), Ameiurus melas Rafineque (Black Bullhead) (~ 0.1%; THN n = 1) and Hiodon alosoides Rafineque (Goldeye) (~ 0.1%; THN n = 1). Tandem hoop nets CPPHE was over 17 times greater than trotlines during this study (W = 79, n = 18, P < 0.01; Table 1). The study design required CPPHE for each gear to be calculated as monthly site mean and then the mean of the monthly sites. Mean length of Channel Catfish was significantly greater in trotlines (X̅ = 377, SE = 24) with lengths ranging from Table 1. Catch standard metrics of channel catfish for trotline (TL) and THN across June, July, August, and months combined in the White River, SD. Descriptive statistics for numeric variables include sample size (n), mean length, mean length range, mean catch per unit effort (CPUE), mean catch per personnel hour effort (CPPHE), time (minute and second) it took to bait, set and pull gear, and standard error (SE). Month Gear N Mean length (range) Mean CPUE (SE) Mean CPPHE (SE) Mean time to bait, set, and pull gear (SE) June THN 366 318 (192–575) 24.4 (8.34) 34.46 (11.01) 16m 32s (2m 2s) TL 21 355 (171–495) 1.47 (0.43) 2.51 (0.76) 15m 44s (1m 51s) July THN 321 327 (179–644) 21.4 (6.15) 38.31 (10.86) 14m 50s (1m 32s) TL 15 392 (250–631) 1.00 (0.28) 1.61 (0.46) 13m 18s (1m 5s) August THN 200 267 (65–642) 13.33 (2.78) 21.58 (4.04) 12m 16s (0m 42s) TL 9 405 (255–585) 0.6 (0.29) 1.16 (0.60) 12m 24s (0m 48s) Total THN 887 310 (65–644) 20.16 (3.10) 35.03 (5.28) 14m 32s (0m 54s) TL 45 377 (171–631) 1.04 (0.20) 1.72 (0.36) 13m 49s (0m 47s) Prairie Naturalist A.E. Gebhard, C.W. Goble, and C.M. Longhenry 2021 53:16–26 21 171 to 631 mm than THNs (X̅ = 310, SE = 12, D = 0.43, P < 0.01; Fig. 3) that had a range in lengths from 65 to 644 mm. Age frequency distributions between gear types were similar (D = 0.157, P = 0.97; Fig. 4). Channel Catfish caught by THN ranged from 0 to 16 years old and were fully recruited at 3 years old with this age class contributing 20% (n = 237) of the catch (Fig. 4), while Channel Catfish captured on trotlines ranged from 1 to 18 years old and were fully recruited at 4 years old with this age class contributing 21% (n = 9) of the catch (Fig. 4). Across months, mean trotline CPPHE was 1.7 fish per personnel hour (SE = 0.4; Table 1), while mean THN CPPHE was 35.0 fish per personnel hour (SE = 5.3; Table 1). Trotline Figure 3. Length frequency distributions and total catch of channel catfish collected from trotlines and tandem hoop net across the study duration (June, July, and August) in the White River, South Dakota. Figure 4. Percent frequency by age of channel catfish for trotlines and tandem hoop nets in the White River, South Dakota. Tandem hoop nets channel catfish percent frequency by age denoted by black bars. Trotline channel catfish percent frequency by age denoted by gray bars. Prairie Naturalist A.E. Gebhard, C.W. Goble, and C.M. Longhenry 2021 53:16–26 22 CPPHE declined from 2.5 fish per personnel hour (SE = 0.8; Table 1) in June to 1.2 fish per personnel hour (SE = 0.6; Table 1) in August; none of the monthly differences were statistically significant (H2 = 0.36, df = 2, P = 0.84). Mean THN CPPHE across all months was not significantly different (H2 = 0.09, df = 2, P = 0.96), ranging from 38.3 fish per personnel hour (SE = 1086) in June to 21.6 fish per personnel hour (SE = 4.0) in August. On average, it took a three-person crew 13 minutes and 49 seconds (SE = 47 seconds) to perform each unit of trotline effort, while a THN three-person crew took 14 minutes and 32 seconds (SE = 54 seconds) to perform each unit of THN effort. Trotline catches across months ranged from 0 to 5 Channel Catfish (mean CPUE = 1.0 fish per hook set; SE = 0.2) with no significant monthly differences (H2 = 2.51, df = 2, P = 0.29; Table 1). Tandem hoop net catches ranged from 0 to 118 Channel Catfish (mean CPUE = 20.1 fish per set; SE = 3.1), but did not statistically differ (H2 = 0.09, df = 2, P = 0.96) across months. Trotline mean and minimum lengths generally increased across months; however, the length distribution differences were not statistically different (H2 = 2.49, df = 2, P = 0.29). Tandem hoop nets mean length was also not significantly different across the temporal scale (H2 = 4.36, df = 2, P = 0.12). Discussion Based on the findings of this study and others (e.g., Arterburn 2001, Bodine et al. 2013, Pugh and Schramm 1998, Vokoun and Rabini 2001), hoop nets seem to provide superior results compared to other common Channel Catfish sampling gears (i.e., trotlines, electrofishing) across a variety of lotic systems. However, even among these studies, hoop net configurations are not universal. Hoop diameters (i.e., 0.6 m, 0.8 m, 1 m, 1.22 m), number of hoops (i.e., 3, 6, 7), bar mesh size (i.e., 13 mm, 25.4 mm, 32 mm, 35 mm), and bait selection (i.e., un-baited, cheese, soy-cake) differ depending on study location and objectives. Seemingly minor differences in net configuration can introduce sampling bias that potentially affects inferences made in monitoring or research studies. Nets with smaller mesh captured smaller Channel Catfish than larger mesh (Holland and Peters 1992, Tillman et al. 1997) and smaller hoop diameter and mesh had greater catch rates (Pugh and Schramm 1998). We sought to alleviate some of these issues by including nets with two different mesh sizes (i.e., 21 mm and 35 mm) in our tandem net configuration. Gear standardization for indexing lotic Channel Catfish populations is a relatively recent occurrence when compared to survey methods for other popular sportfishes, such as Sander vitreus Mitchill (Walleye) or Micropterus salmoides Lacépède (Largemouth bass) (Bonar et al. 2009, Fisheries Techniques Standardization Committee 1992). Methodological differences stem in part from variation in lotic system attributes (e.g., velocity, substrate, order of river, water depth, turbidity, habitat availability) meaning that a “one-size-fits-all” sampling approach may not be appropriate or feasible. However, without some level (e.g., local, regional) of standardization in survey protocols, it is impossible to make rigorous spatial or temporal comparisons in population monitoring programs (Bonar et al. 2009). Like many resource management agencies, the South Dakota Game, Fish and Parks Commission has used a wide variety of sampling gears to capture Channel Catfish over the years. Despite previous gear comparison research (Arterburn 2001), the agency has not adopted standardized protocols for monitoring the species in flashy, turbid, mid-sized rivers that are characteristic throughout much of the state. Multiple criteria have been established for assessing standardized sampling gear including the following: catch rates, fish mortality, representative length distributions, fish mortality, and efficiency (i.e. time required to collect samples [Miller et al. 2018]). Prairie Naturalist A.E. Gebhard, C.W. Goble, and C.M. Longhenry 2021 53:16–26 23 Another issue with gear standardization is how to make comparisons between different gear types, each with their own potential sampling biases. While methods for incorporating and standardizing data from multiple survey methods exist (e.g., Gibson-Reinemer et al. 2017), we elected not to statistically compare THN and trotline CPUEs due to unknown differences in gear saturation and escapement rates. Trotline catches are limited by the number of hooks, which in this study allowed a maximum catch of 20 Channel Catfish per trotline. While THNs are also subject to gear saturation (Ricker 1975), maximum potential catches are much greater than those for standard trotline configurations as evidenced by mean THN CPUEs exceeding 20 fish per net night for two of the three months during our study. To address this issue, we looked at sampling efficiency not just as CPUE but CPPHE. By standardizing catch based on the time required to run each gear trotlines had the potential of being a more efficient gear than THNs. However, baiting, setting, and pulling times were similar for both gears indicating that any efficiency benefits of one gear versus the other would have to come from increased numerical catch (CPUE) rather than reductions in time. Based upon our findings and the suggested criteria for evaluating sampling gears (Miller et al. 2018), the catch rates of the trotlines we used were too low to be an effective sampling gear for Channel Catfish in the White River when compared to THN without significant improvements in ef ficiency. Sampling Channel Catfish in the White River did present some challenges. Retrieval concerns included gear being covered up by sand or floating/submergent debris. We chose to do 24-hour sets to minimize the chances of our gear to become buried by sand and debris. Recommendations from Michaletz and Sullivan (2002) and Neely and Dumont (2011) suggest net sets of 2–3 days for lower sampling variability and higher catch/hour. Our catch rates (CPUE 20.2) were similar for only 24-hour sets compared to Bodine et al. (2013) who found the commonly used THNs had a median 20.7 CPUE for 48–72 hour sets. We did end up losing 1 trotline and 1 THN during the July sampling period due to gear becoming completely covered by sand. However, we did not observe substantial mortality in any of our gear deployments regardless of month. Timing of Channel Catfish sampling may affect standard catch metrics. Vokoun and Rabeni (2001) found in Missouri that October hoop net sampling in three streams of the Grand River basin resulted in higher CPUEs and level of sampling precision than June and August sampling. However, seasonal differences in sampling efficiency and precision do not appear to be universal. For example, Schall et al. (2020) determined that gill net sampling demonstrated similar population dynamics during spring and fall surveys in Lake McConaughey in western Nebraska. The time frame of this study was limited to the summer months (June, July and August), but our results indicated no significant differences in length distribution or CPUE across the temporal scale. However, future research should be conducted to determine if early spring (April or May) or fall (October) would be a better time to sample using THN. Management Implications While fisheries managers have a wide range of gears (e.g., gill nets, electrofishing, trotlines) available to sample lotic Channel Catfish populations, there is no universally accepted “best” method and gear choice often remains a system-specific decision. This short study suggests that THN is the superior gear choice to assess Channel Catfish growth, age structure for individuals three years and older, and relative populations trends in the White River in South Dakota and possibly other Missouri River tributaries. Tandem hoop net sampling would help managers make more informed management decisions regarding populations in these larger tributaries of the Missouri River and the Missouri River itself in South Dakota. Prairie Naturalist A.E. Gebhard, C.W. Goble, and C.M. Longhenry 2021 53:16–26 24 This approach of testing various gears before deciding on a standard gear is critical to making sure managers are selecting the proper sampling gear for specifi c types of systems. In terms of sampling efficiency, THNs dramatically outperformed another commonly used Channel Catfish sampling gear, baited trotlines, with regards to overall numbers, sizes of fish collected, and personnel effort (i.e., time) required. Due to the seasonally migratory nature of Channel Catfish in lotic systems (Butler and Wahl 2011, Dames et al. 1989), survey timing likely plays an important role in the estimation of population indices. While the temporal differences in Channel Catfish catch-rates and size-structure observed in this study were not significant, care should be taken when designing studies to estimate population parameters. It appears that tandem hoop net sampling conducted during the summer months (June, July, and August) will likely produce similar results in South Dakota’s White River. However, due to the limited time frame and lack of repetition of this study, we are unable to determine how those results might compare to sampling conducted during the spring or fall. Tandem hoop net configurations (e.g., net lengths, mesh size combinations), sample timing, set duration, and bait selection can and should be modified to reflect differences between specific study systems, and we recommend managers perform preliminary assessments such as this prior to implementing sampling programs for making management decisions. Acknowledgments This pilot project could not have been completed without the assistances from the South Dakota Game, Fish, and Parks Fisheries and Habitat staff out of the Chamberlain office helping with field work and the assistances from the South Dakota Game, Fish, and Parks Ft. Pierre Fisheries staff with lab work. We would like to thank L. DeHaai for the donation of the waste cheese used during this pilot study. A special thanks to G. Adams and M. Barnes for constructive comments regarding this pilot project and manuscript construction. This project was made possible from funding by the South Dakota Game, Fish, and Parks. Literature Cited Arterburn, J.E., 2001. Population characteristics and sampling methods of catfish for the James and Big Sioux Rivers. Thesis. South Dakota State University, Brookings, SD, USA. 88 pp. Arterburn J.E., and C.R. Berry, Jr. 2002. Effect of hook style, bait type, and river location on trotline catches of flathead and channel catfish. 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