Long-Term Data Suggest Potential Interactions of Introduced Walleye and Smallmouth Bass on Native Sauger in Four Missouri River Impoundments

Home , Lake Sharpe, Lewis and Clark Lake

Natural Resource Ecology and Management Publications Natural Resource Ecology and Management

12-2019

Mark J. Fincel South Dakota Department of Game, Fish and Parks

Nicholas B. Kludt South Dakota State University

Hilary A. Meyer South Dakota Department of Game, Fish and Parks

Michael Weber Iowa State University, [email protected]

Christopher M. Longhenry South Dakota Department of Game, Fish and Parks

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This Article is brought to you for free and open access by the Natural Resource Ecology and Management at Iowa State University Digital Repository. It has been accepted for inclusion in Natural Resource Ecology and Management Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Long-Term Data Suggest Potential Interactions of Introduced Walleye and Smallmouth Bass on Native Sauger in Four Missouri River Impoundments

Abstract Sauger Sander canadensis, Walleye Sander vitreus, and Smallmouth Bass Micropterus dolomieu, are important sportfish in the four main stem Missouri River reservoirs in South Dakota: Lakes Oahe, Sharpe, Francis Case, and Lewis and Clark. However, native Sauger populations, once assumed to be stable, may be in decline. To identify temporal trends and potential interspecific mechanisms affecting Sauger populations, we examined their long-term abundance trends in standard gillnet surveys and angler catch and harvest trends in long-term creel surveys. We also used a robust design occupancy model to examine changes in within-lake distribution of this species. There are concerns regarding the effects of Walleye and Smallmouth Bass on Sauger, so we also described the population trends of these potential competitors. Standard gillnet surveys indicated declining abundance of both Sauger and Walleye in Lakes Oahe and Sharpe. Sauger abundance has trended down in Lewis and Clark, but upward in Francis Case. Conversely, Walleye abundance trends declined in Francis Case and increased in Lewis and Clark. Occupancy (ψ̂) of Sauger declined in all four reservoirs, indicating a contracting distribution throughout the reservoirs. Walleye occupancy remained ∼1.0. Smallmouth Bass occupancy increased in the three reservoirs with sufficient data for analysis, cludingex Lewis and Clark Lake. Smallmouth Bass exhibited steady increases in angler catch and harvest, as well as abundance in long-term gillnet surveys, suggesting expanding and increasing populations. Habitat alteration is hypothesized to be a major driver of the Sauger occupancy and abundance declines. However, Walleye and Smallmouth Bass interactions could also be contributing to observed declines of native Sauger.

Keywords Lake Francis Case, Lake Lewis and Clark, Lake Oahe, Lake Sharpe, long-term trend data, occupancy modeling

Disciplines Aquaculture and Fisheries | Ecology and Evolutionary Biology | Natural Resources Management and Policy

Comments This article is published as Fincel, Mark J., Nicholas B. Kludt, Hilary A. Meyer, Michael Weber, and Christopher M. Longhenry. "Long-term data suggest potential interactions of introduced Walleye and Smallmouth Bass on native Sauger in four Missouri River impoundments." Journal of Fish and Wildlife Management 10 (2019). doi: 10.3996/122018-JFWM-115.

This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/nrem_pubs/333 Surveys Long-Term Data Suggest Potential Interactions of Introduced Walleye and Smallmouth Bass on Native Sauger in Four Missouri River Impoundments

Mark J. Fincel,* Nicholas B. Kludt, Hilary A. Meyer, Michael Weber, Christopher M. Longhenry

M.J. Fincel, H.A. Meyer South Dakota Department of Game, Fish and Parks, Ft. Pierre District Office, 20641 SD HWY 1806, Ft. Pierre, South Dakota 57532

N.B. Kludt South Dakota State University, SNP 141c, Box 2140B, Brookings, South Dakota 57007

M. Weber Iowa State University, 207 Science Hall II, Ames, Iowa 50011

C.M. Longhenry South Dakota Department of Game, Fish and Parks, Chamberlain Regional Office, 1550 East King Avenue, Chamberlain, South Dakota 57325

However, native Sauger populations, once assumed to be stable, may be in decline. To identify temporal trends and potential interspecific mechanisms affecting Sauger populations, we examined their long-term abundance trends in standard gillnet surveys and angler catch and harvest trends in long-term creel surveys. We also used a robust design occupancy model to examine changes in within-lake distribution of this species. There are concerns regarding the effects of Walleye and Smallmouth Bass on Sauger, so we also described the population trends of these potential competitors. Standard gillnet surveys indicated declining abundance of both Sauger and Walleye in Lakes Oahe and Sharpe. Sauger abundance has trended down in Lewis and Clark, but upward in Francis Case. Conversely, Walleye abundance trends declined in Francis Case and increased in Lewis and Clark. Occupancy (wˆ ) of Sauger declined in all four reservoirs, indicating a contracting distribution throughout the reservoirs. Walleye occupancy remained ~1.0. Smallmouth Bass occupancy increased in the three reservoirs with sufficient data for analysis, excluding Lewis and Clark Lake. Smallmouth Bass exhibited steady increases in angler catch and harvest, as well as abundance in long-term gillnet surveys, suggesting expanding and increasing populations. Habitat alteration is hypothesized to be a major driver of the Sauger occupancy and abundance declines. However, Walleye and Smallmouth Bass interactions could also be contributing to observed declines of native Sauger.

Keywords: Lake Francis Case; Lake Lewis and Clark; Lake Oahe; Lake Sharpe; long-term trend data; occupancy modeling Received: December 11, 2018; Accepted: May 17, 2019; Published Online Early: May 2019; Published: December 2019 Citation: Fincel MJ, Kludt NB, Meyer HA, Weber M, Longhenry CM. 2019. Long-term data suggest potential interactions of introduced Walleye and Smallmouth Bass on native Sauger in four Missouri River impoundments. Journal of Fish and Wildlife Management 10(2):xx–xx; e1944-687X. https://doi.org/10.3996/122018-JFWM-115 Copyright: All material appearing in the Journal of Fish and Wildlife Management is in the public domain and may be reproduced or copied without permission unless specifically noted with the copyright symbol &. Citation of the source, as given above, is requested.

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The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service. * Corresponding author: [email protected]

Introduction Sauger abundance was declining using long-term standardized gillnet surveys; 2) determine whether Sauger Sander canadensis is an important sport fish Sauger occupancy was declining, as an indicator of species throughout its native range. A top tier predator, possible within-reservoir range contraction, and 3) use the Sauger is closely associated with turbid lotic systems long-term creel surveys to document potential concur- (Scott and Crossman 1973). As with many native species, rent changes in angler catch and harvest of Sauger. We alterations of habitat and biological communities replicated these analyses with Walleye and Smallmouth through time may have had detrimental effects. The Bass. There is controversy as to the effects of Walleye and impoundment of reservoirs in Sauger native habitat and Smallmouth Bass on Sauger, so describing their popu- the transition from a lotic to lentic system, with lation and occupancy trends may prove useful in attendant sport fish stockings, have the potential to explaining potential changes in Sauger population negatively affect Sauger populations. characteristics. Sauger were once common throughout the Missouri River basin (Bailey and Allum 1962; Jones 1963; Cross Study Site 1967). Human alterations of the Missouri River, starting in the early 1900s and peaking with the construction of The Missouri River is the longest river in North six major main-stem dams, were associated with America, flowing 3,768 km and draining 1,371,017 km2 declines in Sauger abundance and distribution. Pro- through a network of 47 tributaries with drainage basins posed mechanisms driving declining trends include .1000 km2 (Galat et al. 2005). The South Dakota portion habitat alteration, competition and/or hybridization of the Missouri River is impounded, forming Lakes Oahe, with Walleye Sander vitreus, angler harvest, and/or Sharpe, Francis Case, and Lewis and Clark in rural central competition with Smallmouth Bass Micropterus dolo- South Dakota (upstream to downstream; Figure 1). All six mieu (Galat et al. 2005). Declining trends in Sauger of the major Missouri River impoundments can be abundance were readily apparent in free-flowing classified as ‘‘large’’ compared with other North Amer- stretches of the Missouri River, as well as in main stem ican reservoirs. Lake Oahe is the second largest of these Missouri River reservoirs following impoundment (Nel- six impoundments on the Missouri River and extends son and Walburg 1977). However, little research has from Riverdale, North Dakota to Pierre, South Dakota. At focused on the long-term population trends of Sauger normal pool, the South Dakota portion of Lake Oahe has after the initial studies, which finished soon after the a surface area of ~145,000 ha with a mean depth of ~19 closure of the Missouri River impoundments in the mid- m and a maximum depth of 67 m. Lake Sharpe is the to late 1900s. second smallest Missouri River impoundment extending In South Dakota, Sauger are readily harvested by from Oahe Dam to Big Bend Dam. Lake Sharpe has a anglers. When the Missouri River reservoirs were initially surface area of ~24,686 ha with a mean and maximum filled, Sauger were an important sport fish (Nelson and depth of 9.5 and 23.5 m. Lake Francis Case is the fifth Walburg 1977). Below Oahe Dam from July 1959 to most downstream reservoir on the Missouri River and March 1960, .31,000 Sauger were harvested (Bailey and extends from Big Bend Dam to Fort Randall Dam. At Allum 1962). Similarly, nearly 72,000 Sauger were normal pool, Lake Francis Case has a surface area of harvested below Gavins Point Dam in 1958 (Orr 1962). ~41,000 ha, with mean and maximum depths of 15.2 These Sauger sport fisheries soon substantially declined; and 42.6 m, respectively. Lake Lewis and Clark is the however, populations were thought to stabilize soon smallest and furthest downstream reservoir on the thereafter. Now, anecdotal evidence suggests that the Missouri River. Lewis and Clark Lake extends from Fort Sauger sport fishery has continued to decline over the Randall Dam to Gavin’s Point Dam. At normal pool, Lewis past 30 y. Generally, it was noted that fewer Sauger were and Clark Lake has a surface area of 10,500 ha, and is being sampled or caught by anglers in fewer places. considerably shallower than the other three study These anecdotes, along with the lack of recent study, reservoirs with mean and maximum depths of 5.0 and motivated our examination of the long-term trends of 16.7 m, respectively. Sauger in South Dakota’s main stem Missouri River Each of the reservoirs follow the typical productivity reservoirs. Given the diversity of habitats between pattern for reservoirs (Fincel 2011). The upper reaches reservoirs, we were also concerned with both abundance are considered cold, oligotrophic riverine conditions and distribution trends. largely dictated by the cold-water releases of upper To document changes of these important sport reservoirs. As you move downstream in the reservoirs, fisheries through time, we decided to use a multifaceted transition zones appear and local inputs serve to approach. Our objectives were to 1) determine whether increase nutrient inputs and algal and zooplankton

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Figure 1. Current depiction of the Missouri River impoundments in central South Dakota, USA. Black rectangles represent locations of dam structures.

production increases. In some cases, productivity can Methods approach mesotrophic or borderline eutropic states in these transition zones (Fincel 2011). Then by the lower Population surveys end of the reservoirs, nutrients are largely used up and The South Dakota Department of Game, Fish, and algal and zooplankton density declines appreciably. Parks (SDGF&P) conducted standard coolwater-fish Lake Oahe experiences a strong thermocline in all years population surveys from 1984 through 2016 on Lakes and Lake Francis Case experiences a thermocline in Francis Case and Lewis and Clark (n ¼ 32 y), 1985 through most years. However, Lake Sharpe and Lewis and Clark 2016 on Lake Oahe (n ¼ 31 y), and 1986 through 2016 on rarely see the development of a thermocline (Fincel Lake Sharpe (n ¼ 30 y). The department conducted 2011). surveysinAugust(LakesOaheandSharpe)and All the reservoirs have similar species assemblages September (Lakes Francis Case and Lewis and Clark) at with Walleye, Smallmouth Bass, and Sauger as primary standard sites (Lake Oahe, n ¼ 9; Lake Sharpe, n ¼ 6; Lake predator species. All reservoirs also contain low Francis Case, n ¼ 9, Lake Lewis and Clark, n ¼ 4). At each abundances of Northern Pike Esox lucius, Crappy spp. site, surveyors deployed three gillnets in a straight line Pomoxis, and White Bass Morone chrysops.Allthe from anchor to anchor, pulled nets taught, and set them reservoirs have also been stocked with Rainbow Trout Oncorhynchus mykiss and/or Brown Trout Salmo trutta overnight (~20 h) and on the bottom within depth in the cold water tailraces in various years. Lake Oahe is zones of 0–10 m and 10–20 m for 3–6 nets/site. unique in that Chinook Salmon O. tshawytscha have Surveyors randomly set nets parallel and transverse to been stocked annually since the late 1980s. Common bottom contour lines. If part or all of the gillnet was prey fish species include Gizzard Shad Dorosoma unfishable due to wind or wave action, surveyors cepedianum, Yellow Perch Perca flavescens, Spottail disregarded the partial catch in that net as not Shiner Notropis hudsonius, Emerald Shiner N. atheri- influencing estimates of catch rates, and they reset the noides, and various age-0 sport fish (Fincel 2011; Fincel gillnet as soon as possible. Gillnets were constructed of et al. 2014). multifilament nylon and were 91 m 3 2 m, had a 0.5

Journal of Fish and Wildlife Management | www.fwspubs.org December 2019 | Volume 10 | Issue 2 | 3 Walleye and Smallmouth Bass Interactions Affect Native Sauger M.J. Fincel et al. hanging ratio, with 15-m panels with sequentially unlikely because surveyors physically removed all fish increasing bar mesh sizes: 13, 19, 25, 32, 38, and 51 from gillnets and identified them to species. mm. Surveyors kept effort constant within each reservoir We transformed our gillnet abundance data to for the study period. Surveyors identified captured fish to presence–absence data. Consequently, a site that was species using common phenotypic characteristics; and sampled with 6 gillnets and caught the desired fish on measured, weighed, and removed otoliths from a subset the first, third, and fourth net would result in a detection of individuals for age and growth analysis. We omitted history (hi) of 101100. A single individual captured in any any potential Sander phenotypic hybrids from this study. of the nets would result in an occupied site. Detection We assumed that standardized use of gillnetting and occupancy probabilities are formulated simulta- throughout the study period would represent temporal neously; hence, the hi ¼ 101100 would report the site as variation of each species’ underlying abundance, and occupied but the species was not detected by the that species-specific differences in catchability did not second, fifth, or sixth net. Thus, the probability of change through time (Fincel et al. 2015). We analyzed occupancy for that site would be 1 and the detection within-reservoir abundance trends with linear regres- probability calculated therein: sions, and examined correlations between annual W P 3 1 P 3 P 3 P 3 1 P 3 1 P abundance. Smallmouth Bass were not caught in i ¼ 1 ð 2Þ 3 4 ð 5Þ ð 6Þ standard surveys until 2011 in Lake Lewis and Clark where W is the site-specific occupancy probability, Pj is and infrequently after that. Thus, we did not analyze the probability of detecting the species in the jth survey trend data for Smallmouth Bass in this reservoir. given it is present. Sites where no fish were caught still Nonetheless, anecdotal evidence suggests an increasing have a probability of occupancy despite no individuals population since the 1980s when Smallmouth Bass were being caught. For this analysis, we combined several stocked but the magnitude is not currently discernible. years of standardized surveys in a robust design similar Variability in species abundance is common in these to that of Pollock’s robust design for mark–recapture types of long-term studies. Thus, reviewing the general studies (Pollock 1982), where each year represents a trends is important because variability around the mean primary sampling period and each sampling site is generally high as strong or weak year-classes emerge. represents secondary periods (MacKenzie et al. 2003). Moreover, yearly sampling conditions such as high winds Thus, 3 y of survey data for a single site could yield a or inclement weather can greatly influence abundance detection history of estimates further increasing yearly variability. Thus, caution must be taken when interpreting year-to-year hi ¼ ‘101100 000000 100100’ variability in long-term gillnet data. where a space was inserted between yearly sampling events. From this, we know that the species was present Occupancy modeling in the first and third year but either not detected or Occupancy modeling has been used to assess habitat absent during the second year. We can then use our use by various species (Moore et al. 2017), estimate parameters of detection–nondetection data through species co-occurrence (Richmond et al. 2010; Peoples probability statements to assign a probability of 1) and Frimpong 2015), or evaluate detection probabilities occupied but not detected, or 2) not occupied during between various sampling gears (Moore et al. 2017). the second year of sampling. Detection probabilities are Occupancy analyses assume 1) closure of the sample unlikely to remain constant between primary sampling population, 2) no false detections at a sampling location, periods (MacKenzie et al. 2003); therefore, we used year- and 3) detection of a species is independent between specific detection probabilities in our occupancy model. sites (MacKenzie et al. 2002). We used a robust design We also assumed colonization and extinction probabil- occupancy model in Program MARK (White and Burnham ities to be time-dependent, so we did not bind these 1999) to estimate extinction probability (e), probability of parameters. Our specific question is to identify trends in detection (P) and lakewide occupancy (w) similar to that occupancy of these three sport fish, so we modeled and/ used in Weber and Brown (2019). Long-term standard- or compared no covariate or co-occurrence trends. Here ized gillnet data were used to construct encounter we assume sampling locations encompass the various histories for occupancy models. Although the standard habitats available within the reservoirs and present the experimental design for occupancy models suggests results as lake-wide occupancy estimates (percent of the multiple site visits over a closed period of time, spatially lake occupied by a particular species) through time. distinct replicates can be substituted for temporal replicates at a reduced cost while performing better Creel surveys than temporally replicated data in some instances (Baker The SDGF&P conducted standardized creel surveys et al. 2017). Hence, we used multiple gillnet sets at each yearly from 1991 through 2016 for Lakes Oahe, Sharpe, sampling location as spatially distinct samples. Surveyors and Francis Case (n ¼ 25 y). The SDGF&P reported catch sacrificed all fish caught in a gillnet so there was no rate and harvest for all years, but reported total catch chance of the same individual being counted at separate only in Lake Sharpe starting in 1992. The SDGF&P sampling locations. Moreover, false detections were conducted creel surveys on Lake Lewis and Clark in 1994,

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1995, 2000, 2001, 2005, 2006, 2009, and 2010 only. Robson and Jones method (Robson and Jones 1989). The Additionally, it reported only harvest (#) and harvest rate SDGF&P applied estimated angling pressure for each (#/angler-h) for Lewis and Clark Lake. zone and month to the angler interviewed–derived catch The SDGF&P patterned angler use and sport-fish and harvest estimates to determine lakewide estimates harvest surveys conducted on Lake Oahe and Lake using Creel Application Software. Sharpe prior to 2003 after a study designed by Schmidt On Lake Lewis and Clark, creel surveys were infrequent (1975). Sampling included aerial boat and shore angler and conducted by South Dakota Game, Fish, and Parks as counts along with angler interviews at lake access sites. well as the Nebraska Game and Parks Commission. They The SDGF&P conducted ~12 flights monthly for the used a random stratified roving creel survey design to open-water angling season (May–October), 6 weekday, gather catch data from anglers described for Lake Oahe and 6 weekend or holiday flights. The SDGF&P selected (Malvetuto 1996). They collected instantaneous pressure interview dates using a stratified random design based counts at both access sites (methods described for Lake on the assumption of differential levels of fishing Francis Case) and using a plane (methods described for pressure for weekdays, weekend days, and holidays with Lake Oahe). Similar to other reservoirs, they applied approximately half of the creel shifts occurring on zone-specific monthly data collected from angler inter- weekends or holidays. Additionally, the SDGF&P sepa- views to pressure counts to determine lake wide rated lakes into three (Lake Oahe) or two (Lake Sharpe) estimates using Creel Application Software. For a more approximately equal-sized zones with equal interview detailed description of Lake Lewis and Clark creel effort captured within each zone. Creel clerks spent surveys, see Bouska and Longhenry (2010). between 12 and 18 d creeling within each zone each Obviously, there is an inherent bias associated with month, routinely capturing between 400 and 600 creel surveys (Pollock et al. 1994; McCormick et al. 2013). interviews lake-wide per month. The SDGF&P assigned In particular, when comparing species-specific harvest specific lake-access areas selected for angler interviews results, care must be taken. For instance, Sullivan (2003) using a stratified random design whereby creelers were found anglers exaggerated Walleye catches as a function given a starting location and roved to adjacent access of catch rates. Additionally, inherent bias in the angler points in an attempt to gather as many interviews as preference for harvest is apparent on the Missouri River possible. The SDGF&P included incomplete trips in this reservoirs, with most anglers frequently harvesting analysis and applied zone and monthly estimates of trip Walleye, fewer anglers preferring to harvest Sauger, length, catch, and harvest estimates to zone and and even fewer harvesting Smallmouth Bass (Fincel et al. monthly estimates of pressure counts to determine 2012a, 2012b). Additionally, angler attitudes regarding lakewide estimates using Creel Application Software. For Smallmouth Bass must be taken into account. In the mid- a more detailed description of aerial count, angler interview, and data expansion techniques, see Stone et 2000s, a protected slot limit was enacted on Smallmouth al. (1994) and Fincel et al. (2012a). Bass but this regulation was generally unaccepted by Beginning in 2003, a bus-route survey design (Jones anglers and the regulation was eventually removed in and Robson 1991) replaced aerial counts on Lake Sharpe 2012 (Fincel et al. 2015). Thus, care must be taken when to increase the statistical reliability of the pressure interpreting estimates of catch and harvest of Small- estimates similar to that used for Lake Francis Case mouth Bass in our long-term creel surveys. (Soupir et al. 2006; Sorenson and Knecht 2010). For Lake Francis Case and Lake Sharpe (2003 through 2016), the Results SDGF&P used a bus route design (count interval method) to estimate angler catch, harvest, and pressure. Here, the Population surveys creel clerk waits for a specified period of time In general, Sauger abundance is declining (negative proportional to the expected pressure at the site, and slope) on Lakes Oahe, Sharpe, and Lewis and Clark but then travels to the next location. Upon arrival to an increasing on Lake Francis Case (positive slope; Table 1, access location, creel clerks would record the initial Figure 2; Table S1, Supplemental Material). Interestingly, number of shore anglers and boat trailers present and Walleye abundance is also declining on Lakes Oahe, departure times of anglers. The creel clerk would also Sharpe, and Francis Case (Figure 3). Smallmouth Bass interview anglers as they left the access site to document abundance is increasing in Lakes Oahe, Sharpe, and catch, harvest, and time spent fishing. Lakes were Francis Case (Figure 4). Sauger and Walleye correlation divided into three (Lake Sharpe) or five (Lake Francis coefficients were negative in Lakes Oahe and Francis Case) logical zones with starting routes, travel direction, Case (Table 2) as a result of inverse population trends and creel shift beginning and ending times randomized (Figures 2 and 3), whereas positive coefficients in Lakes for each creel shift. The SDGF&P included incomplete Sharpe and Lewis and Clark reflected the concurrent trips in this analysis. The SDGF&P calculated pressure decline. Sauger and Smallmouth Bass correlation coeffi- estimates based on day type, access site, route cients were all negative (Table 4). This is likely due to the probability, work shift probability, wait time at the declines in Sauger abundance (Figure 2) and concurrent access site, total route length, and user ratio using the increases in Smallmouth Bass (Figure 4).

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Table 1. Linear regression coefficients for mean catch per unit effort (CPUE; #/net) and occupancy (wˆ ) of Sauger, Walleye, and Smallmouth Bass for four Missouri River reservoirs (Lakes Oahe [1985–2016], Sharpe [1986–2016], Francis Case [1984–2016], and Lewis and Clark [1984–2016]) in South Dakota, USA. Bold text represents significant model fit (a 0.2). Sauger Walleye Smallmouth Bass r2 P Intercept Slope r2 P Intercept Slope r2 P Intercept Slope Abundance (CPUE) Lake Lewis and Clark 0.12 0.05 238.8 0.12 0.08 0.11 195.8 0.10 — — — — Lake Francis Case 0.53 ,0.01 312.3 0.16 0.30 ,0.01 766.5 0.38 0.01 0.81 3.5 0.01 Lake Sharpe 0.05 0.22 80.5 0.04 0.22 ,0.01 729.0 0.35 0.43 ,0.01 64.3 0.031 Lake Oahe 0.02 0.46 10.9 0.01 0.01 0.64 117.8 0.05 0.49 ,0.01 129.2 0.07 Occupancy (wˆ ) Lake Lewis and Clark 0.34 ,0.01 12.4 0.01 0.12 0.05 7.6 0.01 —— — — Lake Francis Case 0.05 0.24 7.9 0.01 0.06 0.17 3.0 0.01 0.26 0.01 22.4 0.01 Lake Sharpe 0.40 ,0.01 21.2 0.01 0.04 0.27 3.0 0.01 0.32 ,0.01 38.6 0.02 Lake Oahe 0.30 0.08 15.4 0.01 —— — —0.50 ,0.01 32.0 0.02

Occupancy modeling surveys, Sauger show an increasing trend in catch and Trends in occupancy suggest a long-term decrease in harvest on Lake Francis Case. Both fish population and site occupancy within all four reservoirs for Sauger (Table angler accounts are therefore providing complimentary 1; Table S2, Supplemental Material). However, Lake information. Francis Case exhibited the slightest Sauger decline of Lake Francis Case exhibited the only positive abun- all reservoirs. In general, Walleye site occupancy is dance trends for Sauger in South Dakota Missouri River decreasing on Lakes Sharpe and Francis Case but reservoirs. Looking more finely into the Francis Case data increasing on Lake Lewis and Clark. Walleye occupied set, we found that a single site was showing marked 100% of the sites throughout the duration of the analysis increases in Sauger catches. That site was in close on Lake Oahe; hence, we performed no trend analysis. proximity to the White River, a large, turbid tributary. Lakes Oahe, Sharpe, and Francis Case exhibited increas- Although Sauger are becoming rarer throughout the ing trends in site occupancy for Smallmouth Bass. lake, it appears this area has been promoting the increased abundance of Sauger in Lake Francis Case.

This is unsurprising because Sauger are spatially Creel surveys associated with the turbid, flowing tributaries that Sauger exhibited a decreasing trend in angler harvest approximate their original riverine habitat. The White (#), catch (#), and catch rate (#/angler-h) on Lakes Oahe River flows year round but can have seasonal floods that and Sharpe and a decreasing trend in harvest (#) and pour fine sediments into the lake. This unique feature harvest rate (#/angler-h) on Lake Lewis and Clark (Table could likely aid in the persistence of Sauger in Lake S3, Supplemental Material). Contrary, Lake Francis Case Francis Case. This tributary’s turbid water could be used documented an increase in Sauger harvest, catch, and as a spawning and foraging location. For instance, the catch rate (Table 3, Figure 5). Both Walleye and Small- majority of Sauger spawning was thought to take place mouth Bass exhibited increasing trends in harvest, catch, below the Powder River tributary of the Yellowstone and catch rate in Lakes Oahe, Sharpe, and Francis Case River, which is a major source of fine sediments (Figure 6 and 7), and an increasing trend in harvest and (Rehwinkel et al. 1978). The largest spawning aggrega- harvest rate on Lake Lewis and Clark (Figure 8). tion of Sauger in the Little Wind River system occurred Regression coefficients are presented in Table 3 for just downstream of Beaver Creek, a large source of warm Lakes Francis Case, Sharpe, and Oahe; whereas, Lewis turbid water (Kuhn et al. 2008). The turbid waters and Clark coefficients are in Table 4 to account for entering Lake Francis Case could also be facilitating different temporal range. increased foraging efficiency for Sauger whose eyes are adapted to highly turbid, low-light situations (Ali and Discussion Anctil 1977). Moreover, growth of Sauger in the Missouri River varies among latitudes and subsequent degree It appears Sauger are declining in three of the four growing days, suggesting improved growth in warmer South Dakota Missouri River impoundments over the waters (Braaten and Guy 2002). The warm water past 30 y. Both site occupancy rates and overall discharge could be providing a thermal refuge unique abundance indicate the population is declining and to Lake Francis Case. spatial distribution contracting. The only exception to The overarching concern regarding Sauger declines in these observations was in Francis Case where proba- the Missouri River basin has been habitat alteration. bility of occupancy declined despite increases in Sauger populations in the Montana portion of the basin Sauger abundance. Angler information mirrors that have shown a similar decline to South Dakota popula- from standard surveys, with catch and harvest of tions over a similar time scale (McMahon and Gardner Sauger decreasing through time on Lakes Oahe, 2001). Sauger are native to large rivers and the Sharpe, and Lewis and Clark. Also, like the standard anthropogenic changes found throughout the Missouri

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Figure 2. Estimated abundance (catch per unit effort; filled circles) and lake occupancy (wˆ , open circles) of Sauger Sander canadensis collected from standard gillnet surveys in four South Dakota Missouri River impoundments from 1984 to 2016. Long dashes and short dashes represent trend lines for Sauger abundance and lake occupancy, respectively.

River are extensive. Large dams, changes in hydrological stream migrations, are largely limited when systems are regimes, decreased sediment loads and turbidity, chang- impounded like the Missouri River reservoirs. es to water temperature patterns, etc., all pose concerns Sauger hybridization with Walleye may also be to native Sauger. The highly migratory nature of the contributing to the declining trends. In Lake Lewis and Sauger is thought to be severely affected by barriers. In Clark, hybridization rates rose from 10% to 21% of Sander the unimpounded Yellowstone River, Sauger migrations spp. between 1995 and 2002 (Van Zee et al. 1996; Graeb between spawning and home areas were the longest et al. 2010). If hybridization is increasing between the documented (Jaeger et al. 2005), with downstream two similar species, it is likely cumulative hybridization migrations common. These behaviors, especially up- effects may be limiting Sauger populations. For instance,

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Figure 3. Estimated abundance (catch per unit effort; filled circles) and lake occupancy (wˆ open circles) of Walleye collected from standard gillnet surveys in four South Dakota Missouri River impoundments from 1984 to 2016. Long dashes and short dashes represent trend lines for Sauger Sander canadensis abundance and lake occupancy, respectively.

Arnold and Hodges (1995) and Utter (2003), both tion varies spatially and temporally across the Missouri suggest reduced fitness of introgressed populations. River (Bingham et al. 2012). South Dakota rates were all Other Sander populations within the Missouri River basin documented .15 y ago, so hybridization between the have shown high hybridization rates, including 22% in two species may have changed since that time. the Missouri River below Ft. Peck reservoir, 20% in Lake Reviewing current trends in hybridization between Sakakawea in North Dakota, and 20% in the upper reach Sauger and Walleye may prove beneficial in explaining of the Missouri River in Montana (Billington et al. 2006); current Sauger declines. however, a more recent study showed 1.9% hybridiza- We documented mixed Walleye abundance trends in tion in Montana reaches, demonstrating that hybridiza- the Missouri River reservoirs. Lakewide occupancy has

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Figure 4. Estimated abundance (catch per unit effort; filled circles) and lake occupancy (wˆ open circles) of Smallmouth Bass Micropterus dolomieu collected from standard gillnet surveys in four South Dakota Missouri River impoundments from 1984 to 2016. Long dashes and short dashes represent trend lines for Sauger Sander canadensis abundance and lake occupancy, respectively. remained high in all reservoirs, with Walleye present in Walleye have readily been blamed for widespread nearly 100% of the sites annually. This may be a function declines of Sauger throughout its range. Although of intermittent yet adequate recruitment as originally animosity exists, little direct evidence has been pub- noted by Nelson and Walburg (1977), who described the lished solidifying this mechanism. Diet overlap has been establishment of the Walleye fishery in the years following shown in some sympatric populations but can differ reservoir closures. The overall trend is similar to Ivan et al. depending on prey composition and availability. In the (2011), who attributed the long term increase in Lake middle Missouri River, diet overlap between Walleye and Huron Walleye abundance during 1980–2008 to stockings Sauger was high in spring and summer, but declined in and then successful natural reproduction. autumn when benthic fish were more abundant in

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Table 2. Linear regression coefficients of species-specific harvest, catch, and catch rates for Lakes Francis Case, Sharpe, and Oahe in South Dakota, USA, during 1991–2016. Bold text represents significant model fit (a 0.2). Harvest (#) Catch (#) Catch rate (#/angler/h) r2 P Intercept Slope r2 P Intercept Slope r2 P Intercept Slope Sauger Sander canadensis Lake Francis Case 0.50 ,0.01 886,894 445.0 0.34 ,0.01 2,981,641 1,495.6 0.41 ,0.01 5.3 0.00 Lake Sharpe 0.03 0.42 104,470 50.7 0.01 0.59 140,263 673,096.0 0.01 0.99 0.1 0.00 Lake Oahe 0.17 0.03 103,252 51.0 0.22 0.02 164,514 81.4 0.07 0.20 0.2 0.00 Walleye Sander vitreus Lake Francis Case 0.01 0.85 793,134 320.3 0.04 0.35 9,144,723 4,827.2 0.06 0.22 16.1 0.01 Lake Sharpe 0.01 0.74 57,490 342.1 0.01 0.92 391,554 343.0 0.01 0.56 10.3 0.01 Lake Oahe 0.17 0.04 15,847,582 8,054.0 0.14 0.06 50,814,559 25,682.0 0.11 0.11 102.5 0.05 Smallmouth Bass Micropterus dolomieu Lake Francis Case 0.00 0.82 22967 15.1 0.22 0.02 2,007,111 1,020.0 0.27 ,0.01 4.1 0.00 Lake Sharpe 0.16 0.04 548,900 278.5 0.31 ,0.01 6,179,454 3,110.5 0.23 0.01 23.2 0.01 Lake Oahe 0.59 ,0.01 1508,040 756.8 0.38 ,0.01 8,557,525 4,296.0 0.24 0.01 15.2 0.01

Sauger diets (Bellgraph et al. 2008). In lakes and Smallmouth Bass were stocked throughout the reservoirs, diet similarity between Walleye and Sauger Missouri River reservoirs in the 1980s. These populations appears to be more variable. Lake Erie Sauger consumed appear to be increasing, and may be influencing Sauger primarily Freshwater Drum Aplodinotus grunniens and abundance and distribution. In the three reservoirs other demersal prey fishes with macroinvertebrates experiencing Sauger declines, Smallmouth Bass are composing ,1% of the diet by weight (Rawson and becoming more abundant and more widespread. More- Scholl 1978). In contrast, diets of similar-sized Walleye over, a weak negative correlation exists between the contained approximately 30% macroinvertebrates (Raw- species in all three reservoirs examined. Although son and Scholl 1978). A comparative study of Walleye research focusing on direct competition between the and Sauger diets in Lake of the Woods, Minnesota, two species is lacking, there is some evidence that showed that Sauger consumed more demersal fish such Smallmouth Bass competition may be negatively influ- as trout–perch Percopsis omiscomaycus and fewer encing Sauger populations (Galat et al. 2005). To our knowledge, no study has directly measured diet or invertebrates than Walleye (Swenson and Smith 1976). In contrast, Walleye consumed more pelagic prey that resource overlap of the two species. In lieu of Sauger– included Yellow Perch, Cisco Coregonus artedi, and Smallmouth Bass diet comparisons, Walleye and Small- mouth Bass diet studies suggest Smallmouth Bass diets Rainbow Smelt Osmerus mordax (Swenson and Smith tend to include more benthic invertebrates from wider 1976; Swenson 1977). In three of the South Dakota taxa compared with Walleye. In Spirit Lake, Iowa, Liao et Missouri River impoundments, diet breadth and variabil- al. (2002) found Yellow Perch were consistently the ity varied for Walleye and Sauger, with potential overlap dominant component of Walleye diets, whereas Small- in Lake Lewis and Clark but less so in Lake Francis Case or mouth Bass diets included substantial percentages of Lake Oahe (Fincel et al. 2016). However, in most studies, littoral invertebrates, mainly crayfish (Cambarus spp). It diet items of Walleye and Sauger were not limiting and, appears Smallmouth Bass exhibit a more littoral–benthic thus, direct competition is rarely confirmed. Moreover, diet compared with Walleye, and this littoral–benthic Haxton (2015) documented separation of Sauger and diet is more similar to the Sauger diets discussed Walleye by depth strata while foraging. This may be due previously. Thus, it is plausible that Sauger and Small- to eye morphology differences (Ali and Anctil 1977), and mouth Bass may show more diet overlap than either subsequent habitat partitioning based on ambient light species does with Walleye. Although this is not direct levels from either depth or water clarity (Ali and Anctil evidence of diet overlap, it at least gives us a reason to 1968). Ickes et al. (1999) documented strong habitat question the extent of diet overlap of Sauger and partitioning both by depth but also spatially between Smallmouth Bass. the two species. This habitat partitioning between the Additionally, direct consumption of Sander spp. by two species could explain the apparent diet overlap but Smallmouth Bass has been documented in many studies. lack of direct competition. Johnson and Hale (1977), Bacula (2009), and Wuellner et

Table 3. Linear regression coefficients of species-specific harvest, catch, and catch rates for Lake Lewis and Clark, South Dakota, USA, from years 1994, 1995, 2000, 2001, 2005, 2006, 2009 and 2010. Bold text represents significant model fit (a 0.2). Harvest (#) Harvest rate (#/angler/h) r2 P Intercept Slope r2 P Intercept Slope Sauger Sander Canadensis 0.09 0.43 99,188.0 49.0 0.54 0.02 2.7 0.01 Walleye Sander vitreus 0.04 0.60 382,408.0 196.3 0.03 0.64 2.2 0.00 Smallmouth Bass Micropterus dolomieu 0.00 0.90 2,769.7 1.6 0.00 0.99 0.0 0.00

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Table 4. Correlation matrices of Sauger Sander canadensis (SAR), Walleye Sander vitreus (WAE), and Smallmouth Bass Micropterus dolomieu (SMB) gillnet abundance (catch per unit effort) for four Missouri River reservoirs (Lakes Oahe [1985–2016], Sharpe [1986– 2016], Francis Case [1984–2016], and Lewis and Clark [1984–2016]) in South Dakota, USA. Values represent correlation coefficients (r).

Lake Oahe Lake Sharpe Lake Francis Case Lake Lewis and Clark SMB WAE SAR SMB WAE SAR SMB WAE SAR SMB WAE SAR SMB 1.000 — — 1.000 — — 1.000 — — — — — WAE 0.064 1.000 — 0.089 1.000 — 0.451 1.000 — — 1.000 — SAR 0.139 0.107 1.000 0.085 0.523 1.000 0.212 0.258 1.000 — 0.565 1.000

Figure 5. Harvest (#), catch (#), and catch rate (#/angler/h) of Sauger Sander canadensis by anglers in Lakes Oahe, Sharpe, and Francis Case, South Dakota, from 1991 through 2016.

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Figure 6. Harvest (#), catch (#), and catch rate (#/angler/h) of Walleye Sander vitreus by anglers in Lakes Oahe, Sharpe, and Francis Case, South Dakota, from 1991 through 2016. al. (2010), all found low levels of predation on Sander spp. individuals. The exact mechanism for Sauger decline is by Smallmouth Bass. In Spirit Lake Iowa though, young unknown but many questions arise as to the effects of Walleye comprised 24% of Smallmouth Bass diets (Liao et further habitat degradation and interactions with other al. 2004). However, in most cases it was assumed that the sport fish in these systems. Currently, no protective low abundance of Smallmouth Bass at the time meant regulations have been placed on Sauger in South Dakota that population-level effects would be minimal. Nonethe- water bodies. less, with Smallmouth Bass populations increasing in three of the four reservoirs, potential interactions between Smallmouth Bass and Sauger should be further studied. Supplemental Material In conclusion, it appears that Sauger are continuing to decline in the Missouri River impoundments; however, Please note: The Journal of Fish and Wildlife Management small areas are continuing to produce numerous is not responsible for the content or functionality of any

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Figure 7. Harvest (#), catch (#), and catch rate (#/angler/h) Smallmouth Bass Micropterus dolomieu by anglers in Lakes Oahe, Sharpe, and Francis Case, South Dakota, from 1991 through 2016. supplemental material. Queries should be directed to the Table S2. Yearly occupancy (wˆ ) derived from standard corresponding author for the article. gillnet surveys for Sauger Sander canadensis, Walleye Sander vitreus, and Smallmouth Bass Micropterus dolo- Table S1. Yearly abundance (CPUE; #/net) derived mieu from Lakes Lewis and Clark (1984–2016), Francis from standard gillnet surveys for Sauger Sander cana- Case (1984–2016), Sharpe (1986–2016), and Oahe (1985– 2016), South Dakota. densis, Walleye Sander vitreus, and Smallmouth Bass Found at DOI: https://doi.org/10.3996/122018-JFWM- Micropterus dolomieu from Lakes Lewis and Clark (1984– 115.S2 (23 KB DOCX). 2016), Francis Case (1984–2016), Sharpe (1986–2016), and Oahe (1985–2016), South Dakota. Table S3. Yearly estimated harvest (#), catch (#), and Found at DOI: https://doi.org/10.3996/122018-JFWM- catch rate (#/angler/h) derived from standard creel 115.S1 (17 KB DOCX). surveys for Sauger Sander canadensis, Walleye Sander

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Figure 8. Harvest (#) and harvest rate (#/angler/h) of Sauger Sander canadensis, Walleye Sander vitreus, and Smallmouth Bass Micropterus dolomieu by anglers in Lake Lewis and Clark, South Dakota, in 1994, 1995, 2000, 2001, 2005, 2006, 2009, 2010.

Journal of Fish and Wildlife Management | www.fwspubs.org December 2019 | Volume 10 | Issue 2 | 14 Walleye and Smallmouth Bass Interactions Affect Native Sauger M.J. Fincel et al. vitreus, and Smallmouth Bass Micropterus dolomieu from References Lakes Lewis and Clark (years 1994, 1995, 2000, 2001, 2005, 2006, 2009, and 2010), Francis Case (1991–2016), Ali AM, Anctil M. 1968. Correlation between retinal Sharpe (1991–2016), and Oahe (1991–2016), South structure and habitat among Stizostedion v. vitreum Dakota. and S. canadense. Journal of the Fisheries Research Found at DOI: https://doi.org/10.3996/122018-JFWM- Board of Canada 25:2001–2003. 115.S3 (27 KB DOCX). Ali AM, Anctil M. 1977. Retinal structure and function in the Walleye (Stizostedion vitreum vitreum) and Sauger Reference S1. Bouska W, Longhenry C. 2010. Annual (S. canadense). Journal of the Fisheries Research Board fish population and angler use and sportfish harvest of Canada 34:1467–1474. surveys on Lewis and Clark Lake and the lower Missouri Arnold ML, Hodges SA. 1995. Are natural hybrids fit or River, South Dakota, 2009. Pierre: South Dakota Depart- unfit relative to their parents? Trends in Ecology and ment of Game, Fish and Parks. Annual Report No. 10-07. Evolution 2:67–71. Found at DOI: https://doi.org/10.3996/122018-JFWM- Bacula TD. 2009. Smallmouth bass seasonal dynamics in 115.S4 (792 KB PDF). northeastern South Dakota glacial lakes. Master’s thesis. Brookings: South Dakota State University. Reference S2. Fincel MJ, Edwards K, Hanten R, Smith Archived by Webcite at: http://www.webcitation.org/ M, Potter K. 2012a. Annual fish population and angler 78lNoIJPv use, harvest and preference surveys on Lake Oahe, South Bailey RM, Allum MO. 1962. Fishes of South Dakota. Ann Dakota, 2011. Pierre: South Dakota Department of Game, Arbor, Michigan: University of Michigan. Museum of Fish and Parks. Annual Report No. 12-06. Zoology Publication No. 119. Found at DOI: https://doi.org/10.3996/122018-JFWM- Baker LF, Artym KJ, Swanson HK. 2017. Optimal sampling 115.S5 (1.92 MB PDF). methods for modelling the occupancy of arctic Reference S3. Fincel MJ, Potter K, Edwards K, Hanten grayling (Thymallus arcticus) in the Canadian Barren- R, Smith M. 2012b. Annual fish population and angler lands. Canadian Journal of Fisheries and Aquatic use, harvest and preference surveys on Lake Sharpe, Sciences 74:1564–1574. South Dakota, 2011. Pierre: South Dakota Department of Bellgraph BJ, Guy CS, Gardner WM, Leathe SA. 2008. Game, Fish and Parks. Annual Report No. 12-04. Competition potential between saugers and walleyes in nonnative sympatry. Transactions of the American

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