Upstream experience and experimental translocation of invasive bigheaded carps results in increased upstream passage success at a navigation lock in a large river

Fish movements in regulated rivers can be challenging to study because anthropogenic modifications, such as locks and dams, can influence animal behavior. Upper Mississippi River Lock and Dam 19 (LD 19), for example, is an invasive carp movement bottleneck due to an impassable dam. Upstream fish passage at LD19 is restricted to the lock chamber, making it an optimal location to test invasive fish deterrents that could limit further range expansion. Evaluating the effectiveness of experimental deterrents requires baseline knowledge of fish movements and suitable sample sizes of fish encountering the deterrents to ensure adequate statistical power. Some evidence indicates fish with prior upstream experience may return upstream or challenge potential deterrents at a higher rate than fish without such experience. To test how previous upstream experience could increase the rate at which fish moved upstream through a navigation lock chamber, we compared upstream passage through LD 19 using bigheaded carp captured below the dam (downstream‐origin) and two groups of bigheaded carp captured upstream from the dam: those that swam downstream on their own volition (upstream‐origin fish) and those that were captured upstream and translocated downstream of LD 19 (translocated upstream‐origin). Translocated upstream‐origin carp demonstrated the highest rate of upstream passage, with 59% of the fish detected downstream from LD 19 passing upstream during our study. In contrast, downstream‐origin carp made no upstream passages over 2 years. Fish origin was shown to influence upstream passage success. This may be an important consideration for fish passage studies and deterrent evaluations.


| INTRODUCTION
A subset of non-indigenous species have become invasive, and some of these invasive species can cause severe ecological and economic disruptions (Mack et al., 2000).Aquatic invasive species are often particularly difficult to control because of their rapid spread (Green & Grosholz, 2021) and may be more likely to become established compared to terrestrial species (García-Berthou et al., 2005).Both the spread and control of invasive species can be affected by anthropogenic barriers and anthropogenic connections (Crook et al., 2015).
Managing invasive species in heavily modified aquatic landscapes involves a balance between maintaining or restoring connectivity to facilitate the migration of native species while selectively using barriers to prevent the unwanted spread of invasive species (Rahel, 2013).Controlling the spread of aquatic invasive species may entail the use of complete barriers to species' movement or involve selective passage or deterrents if totally severing the connection is not feasible or desirable.In both cases, detailed knowledge of movement patterns in native and invasive fish species is necessary for selective deterrents or barriers to be effective.
Bighead Carp (Hypophthalmichthys nobilis) and Silver Carp (Hypophthalmichthys molitrix), collectively referred to as bigheaded carps, escaped from aquaculture facilities in the 1970s and have subsequently invaded the Mississippi River and many of its larger tributaries (Chick & Pegg, 2001;Kolar et al., 2007).A variety of undesirable changes have occurred in areas with high densities of these species.For example, the high efficiency with which bigheaded carp remove phytoplankton and zooplankton can create strong changes in the base of aquatic food webs (DeBoer et al., 2018;Fritts et al., 2018;Sass et al., 2014) and lead to competition with native species (Irons et al., 2007;Pendleton et al., 2017;Sampson et al., 2009), both of which may contribute to shifts in fish assemblages (Chick et al., 2020;Solomon et al., 2016).Resource managers have undertaken efforts to limit further range expansion to mitigate the negative consequences of bigheaded carp invasions in new areas.
Efforts to prevent the further spread of bigheaded carp have varied depending on the local circumstances.Where complete blockage of upstream migration is feasible, dams (e.g., Lakehurst Dam on the Maquoketa River, Iowa; Rahel, 2013) or electric barriers (e.g., Chicago Sanitary and Ship Canal; Parker et al., 2016) have been installed to prevent colonization.In other rivers, severing connectivity is not feasible for a variety of reasons, such as river size, the importance of commercial traffic, or concerns about the effects on the movement of native species.Management strategies for bigheaded carp in those areas have mainly focused on removing carp above barriers and selective deterrents to reduce upstream propagule pressure (Cupp et al., 2021).
The size and importance of the Mississippi River for commercial barge traffic make efforts to prevent upstream migration of bigheaded carps challenging.However, existing navigation locks and dams are one option for deterrents that could balance the economic need to support navigation with the resource management need to block the further spread of bigheaded carp.The upper Mississippi River (UMR, upstream of the confluence with the Missouri River in St. Louis, MO) is divided into 29 navigation pools, each created by a lock and dam structure.Pools are named sequentially moving downstream, and each pool takes its name from the lock and dam at the downstream end of the pool.Many of the locks and dams in the UMR have at least some periods of the year in which open river conditions exist (i.e., defined as the time when the adjustable spillway gates of the dam are raised out of the water, passing unobstructed water through the gates [Wilcox et al., 2004]).Mississippi River Lock and Dam 19 (hereafter,LD 19) is a hydroelectric dam where open river conditions have never occurred (Turney et al., 2022;Vallazza et al., 2021).
The hydraulic head at this dam from 2017 to 2019 averaged 9.2 m (range = 4.7 m-11.4 m; Turney et al., 2022).Consequently, the lock chamber is the only location through which fish can pass upstream and is a bottleneck to the upstream passage of invasive and native fish species.The structure of LD 19, combined with its location as a dividing point between a high-density bigheaded carp population downstream and low-density bigheaded carp upstream (Anderson et al., 2023;Whitledge et al., 2019), makes it an ideal location for testing deterrents to upstream migration (Fritts et al., 2021;Jackson & Runstrom, 2018).
However, upstream passage rates of bigheaded carp originating from locations downstream from LD 19 appear to be so low as to be inadequate for evaluating potential deterrents.For example, a previous study on bigheaded carp found that less than 1% of bigheaded carp captured in Pool 20, downstream from LD 19, passed through the lock structure at LD 19 (Fritts et al., 2021).Bigheaded carp that were originally tagged in locations upstream from LD 19 and which then migrated downstream to Pool 20 on their own volition appear to return upstream through the lock chamber at a higher rate than fish without such upstream experience, although relatively few fish (n = 18 over 2 years) captured upstream from LD 19 passed downstream into Pool 20 (Fritts et al., 2021).A previous analysis of over 150 bigheaded carps captured upstream from LD 19, in pools 16 through 19, found that six fish swam downstream from LD 19 and later passed upstream through LD 19 (Vallazza et al., 2021).
The strategic importance of LD 19 as a bottleneck for bigheaded carp moving upstream has led to strong interest in testing an experimental deterrent, such as those involving underwater sound (Brey et al., 2023;Vetter et al., 2015Vetter et al., , 2017)), that could reduce bigheaded carp passage without impeding the movement of native species.
Effectively testing any such deterrent, though, requires a suitable sample population; if fish encounter a potential deterrent only rarely, it takes much longer to achieve the statistical power necessary to evaluate how well it performs.Reducing the amount of time needed to robustly evaluate an experimental deterrent is important, particularly when invasive species populations may grow exponentially.Therefore, we examined whether bigheaded carp captured upstream from LD 19 and experimentally translocated and released downstream from LD 19 would have higher upstream passage rates through the lock, and could thereby serve as a model population for future evaluation of experimental deterrents.We hypothesized that (1) bigheaded carp that were captured upstream from LD 19 and experimentally translocated, implanted with a transmitter, and released in Pool 20 downstream from LD 19 (i.e., translocated upstream-origin) would exhibit higher upstream passage rates through LD 19 relative to the upstream passage rates of bigheaded carp captured, tagged, and released in Pool 20 (i.e., downstream-origin), (2) bigheaded carp captured and tagged upstream from LD 19 and migrated downstream to Pool 20 of their own volition (i.e., upstream-origin) would exhibit higher upstream passage rates through LD 19 relative to the upstream passage rates of bigheaded carp captured and tagged in Pool 20 (i.e., downstream-origin), and (3) bigheaded carp captured upstream from LD 19 and experimentally translocated (i.e., translocated upstream-origin) would exhibit similar behavior and timing of passage through LD 19 relative to fish that were captured and tagged upstream from LD 19 then migrated downstream to Pool 20 of their own volition (i.e., upstream-origin).Our secondary objectives were to evaluate the roles of season and fish size on successful upstream passage and to evaluate the relation of fish upstream passage to operation of the lock chamber for river vessels.

| Study area
Lock and Dam 19 is located on the Mississippi River between Illinois and Iowa at river km 586 (Figure 1).The structure includes a 366-m long by 33.5-m wide lock chamber on the right descending bank (i.e., Iowa shore; inset map).The Keokuk Power Plant hydroelectric facility is immediately upstream from the lock approach between the dam and the approach channel, and an ice dam extends upstream from the hydroelectric facility to deflect drifting ice or debris.The dam spans the remaining 1400-m width of the river.Of the 29 lock and dam structures on the upper Mississippi River, LD 19 has the highest hydraulic head.The difference in water levels can be as much as 12 m between Pool 20 (downstream from the dam) and Pool 19 (upstream from the dam), with a minimum of 4.7 m difference during 2017-2019 (Turney et al., 2022).Water from the lock chamber discharges into two locations at this lock and dam (i.e., discharge laterals located in the downstream lock approach plus discharge ports on the river side of the river wall).

| Lock operation data
We used data from the U.S. Army Corps of Engineers Lock Performance Management System on the direction (i.e., upstream and downstream) and type (e.g., commercial and recreational) of traffic transiting the lock chamber to examine potential patterns in specific lock operations for river vessels and successful upstream fish passage through the lock chamber.The lock chamber depth ranges from 3.4 m at low levels (downstream) to 14.9 m at high levels (upstream).This lock averages 2400 lockages per year from mid-March through mid-December (Figure S2).Ice cover on the Mississippi River necessitates the closure of the locks during the winter months.The upstream and downstream lock gates remained closed during this period.

| Fish capture, tagging, and detection
Upstream passage rates between bigheaded carp with and without known experience upstream from LD 19 were compared using data from fish tagged with acoustic transmitters and detected on acoustic telemetry receiver arrays (Table 1).We considered all bigheaded carp captured upstream from LD 19 to have prior upstream experience, although we did not have information about when or whether these fish had previously passed through LD 19.The Illinois Natural History Survey and contracted commercial fishers collected Silver Carp and Bighead Carp from Pool 18 and Pool 19 of the UMR for translocation to Pool 20 in May 2019 (N = 72).Fish receiving transmitters were immediately placed into a standard holding tank (375 L) on a boat containing river water adjusted to a 0.5% salt solution (Wurts, 1995) and then transferred to a fish transportation hauling tank (750 or 940 L) at approximately 1 kg of fish/4 L water containing river water also adjusted to a 0.5% salt solution to reduce stress during transport.Somerville, New Jersey) after insertion of the transmitter.All fish were weighed and measured.Implanted transmitters did not exceed 2% of the fish's body weight (Winter, 1996).Fish were generally exhibiting normal swimming behavior 1-5 min after surgery and were typically held in holding tanks with recirculating water for 15-30 min prior to release into slack water areas in Pool 20, 1-2 km downstream from LD 19.All animal procedures were reviewed and approved by the U.S. Geological Survey Upper Midwest Environmental Sciences T A B L E 1 Description of the capture location, release location, and mechanism for arriving in Pool 20 among three groups of bigheaded carp used in the study.

| Acoustic-receiver array
Fish were monitored at LD 19 using two acoustic telemetry receiver arrays.The focal array was a small-scale receiver system to determine behaviors near the lock and upstream passage through the lock chamber that included 14 VR2-Tx acoustic receivers (VEMCO Innovasea, Nova Scotia, Canada) installed within the downstream lock approach, lock chamber, and upstream lock approach (Figure 1).Receivers were installed in ladder wells to prevent damage and collisions with barges and other vessels.The placement of receivers in ladder recesses did cause a reduced field of view, but the receivers were still able to detect test transmitters throughout the downstream lock approach, lock chamber, and upstream lock approach (Figure S1).

| Factors affecting fish passage
Biological characteristics of fish, such as size, can influence the direction and magnitude of their movements, particularly for largerbodied fish that exhibit annual spawning migrations (Lucas & Baras, 2001).For a subset of fish (i.e., Silver Carp tagged in 2019), we examined the role of fish size on fish movement.We chose this subset because relatively few Bighead Carp (n = 13) were tagged in 2019, and we did not want to introduce extra uncertainty by estimating a growth rate for bigheaded carp tagged multiple years prior to this study.Some fish detected during the study period (2019-2020) had been captured and tagged as early as 2016 (Table 2), and we did not have information on their growth in the intervening years.The 2019 cohort of tagged Silver Carp also provided a way to examine fish size in both downstream-origin fish and translocated upstream-origin fish.

| Statistical analyses
All analyses were performed in R (R Core Team, 2018).We compared the total length of translocated upstream-origin Silver Carp and downstream-origin Silver Carp tagged in 2019 using a Welch twosample t-test (t.test function in R).We used a binomial logistic regression (glm function in R) to evaluate the effect of total length on upstream passage.We were interested only in whether a fish passed upstream during the study period or not, so we classified individuals as having passed upstream or not, regardless of whether they made multiple passages.We evaluated whether the proportion of bigheaded carp passing upstream differed between fish originating upstream from LD 19 and fish originating downstream from LD 19 using a chi-square test (chisq.testfunction in R).We also evaluated whether the proportion of bigheaded carp passing upstream differed between upstream-origin individuals and translocated upstream-origin individuals using a chi-square test.For both analyses involving the proportion of bigheaded carp passing upstream, we used the number of fish making upstream passage to avoid counting multiple passages by the same fish.The statistical significance threshold criterion was α = 0.05.

| RESULTS
In 2019 and 2020, 106 tagged bigheaded carp were detected by acoustic receivers in and around the downstream lock approach of LD 19 (Figure 2).Ping conversion ratios for receivers in the downstream lock approach ranged from 50% ± 4% to 66% ± 4% SE.These data indicate that there was minimal data loss from transmitter signal collisions during our study.Of the 106 individuals, 76 were identified as  headed carp had higher rates of upstream passage (59%, 17/29) than did upstream-origin bigheaded carp that migrated downstream on their own volition (48%, 12/25), but this difference was not statistically significant (χ 2 = 0.6, p = 0.74 df = 1).All upstream fish passages occurred from June through September and most (61%, 19/31) occurred in July (Figure 3).There were many lock openings in months without bigheaded carp passages (i.e., April, May, October, and November; Figure S2).Most (74%, 23/31) upstream passages were initiated when an upstream-bound commercial tow (i.e., the combination of barges and the vessel pushing the barges) entered the lock chamber, and most (58%, 18/31) upstream fish passages were completed when a downstream-bound tow entered the lock chamber.
There was weak evidence that size was positively correlated with an increased likelihood of upstream passage through the lock chamber.Among all Silver Carp tagged in 2019 and detected downstream from LD 19 from 2019 to 2020, the mean total length was 811 mm (range 650-970 mm; n = 32; Figure 4).Total length was not a significant predictor of upstream passage (glm; p = 0.061) for all Silver Carp tagged in 2019, but the total length was a significant predictor of upstream passage among translocated upstream-origin Silver Carp (glm; p = 0.043).Although the test statistics were on opposite sides of the significance threshold (α = 0.05), the magnitude of the effect of total length on fish passage was large.For example, the probability of making a full upstream passage for a fish in the 75th percentile for

| DISCUSSION
In this study, we observed two groups of upstream-experienced bigheaded carp: a group that was experimentally translocated downstream from LD 19 in 2019 (translocated upstream-origin) and a group of fish captured and released upstream from LD 19 that migrated downstream to Pool 20 on their own volition (upstream-origin).Both groups originating upstream from LD 19 displayed higher rates of upstream passage than fish captured downstream from LD 19.Together with the results of an earlier study in the same area from 2017 to 2018 (Fritts et al., 2021), there are four consecutive years (2017-2020) of monitoring data for tagged bigheaded carp from Pool 20.Across these 4 years, bigheaded carp without known upstream experience were documented making full upstream passage through the lock chamber only once (<1%, 1/112).In contrast, more than 30% of upstream-experienced bigheaded carp detected downstream from LD 19 have passed upstream through the lock chamber.The rate of passage by upstream-experienced fish has remained consistently higher than that of downstream-origin fish across the combined 4 years of observations with several individuals completing multiple upstream passages at LD 19.The 4 years of observations provide strong evidence that bigheaded carp with experience upstream from LD 19 pass at a substantially higher rate than do bigheaded carps without known upstream experience.As a result, using bigheaded carp with known experience upstream from LD 19 as a test population for deterrents is likely to increase the sample size of fish that will encounter the deterrents in a shorter time and allow for robust inferences of deterrent effectiveness.
The results we observed indicate upstream movement is consistently associated with season and vessel traffic.We observed strong evidence of a seasonal pattern in upstream fish migration at LD 19 that is consistent with other research on bigheaded carp movements in the UMR (Fritts et al., 2021;Vallazza et al., 2021).Every instance of upstream passage at LD 19 from 2019 to 2020 occurred from June through September in both translocated upstream-origin and upstream-origin bigheaded carp.The same seasonal pattern also held in observations made from 2017 to 2018 (Fritts et al., 2021).Previous research from bigheaded carps surgically implanted with acoustic transmitters from 2014 to 2017 displayed low passage rates at navigation locks and dams in winter months but cautioned that this pattern may be an artifact of removing receivers from the water to avoid ice damage (Vallazza et al., 2021).From 2017 to 2020, receivers were actively deployed near LD 19 throughout the year, so the results we observed likely reflect a true seasonal pattern in upstream fish passage rather than an artifact of monitoring.Another emerging pattern is that most upstream fish passages were initiated when an upstream-bound tow entered the lock chamber, and the successful exit of fish from the lock chamber upstream coincided with the entrance of a downstream-bound tow into the lock chamber, similar to the results documented in 2017-2018 (Fritts et al., 2021).The association may reflect a combination of behavioral impacts, hydraulic influence on fish movement, and the length of time available for fish to enter the lock chamber (Becker et al., 2013;Davis et al., 2017;Maynord, 2005).
There was weak to moderate evidence that larger Silver Carp were more likely to pass upstream through the lock chamber.Our ability to make inferences about the role of fish length was limited by the amount of information we had on how fish length may have changed between the initial tagging and subsequent passage events.The two groups of fish we evaluated, those with and without known upstream experience, were broadly similar in their size distributions and the methods in which they were captured and tagged.Therefore, the results we observed were unlikely to be an artifact of sampling or other factors related to fish capture.For example, there were no meaningful differences in fish size that could explain the difference in upstream passage rates between fish with and without upstream experience.In 2019, the length distributions of downstream-origin individuals were nearly identical to the length distribution of translocated upstream-origin individuals that completed upstream passage through the lock chamber (Figure 4).The length at which 50% Silver Carp reach sexual maturity in the upper Mississippi River basin is 310 mm (Erickson et al., 2021), whereas the smallest Silver Carp in this study was 650 mm; therefore, it is unlikely that differences in sexual maturity among tagged Silver Carp can explain differences in upstream movement.A study on River Lamprey (Lampetra fluviatilis) in England observed that larger lamprey were more likely than smaller individuals to ascend specific barriers (Jubb et al., 2023).Given the biological importance of size and body condition in bigheaded carp (e.g., Coulter et al., 2022), these factors seem likely to increase the rate of upstream movement.
Upstream homing behavior in migratory fishes appears to be common across a variety of freshwater fishes, and several biological mechanisms may explain this behavior (Lucas & Baras, 2001).For bigheaded carp in the UMR, spawning may be the primary reason for adult fish to move upstream.Bigheaded carp are pelagic spawners, and their eggs and larvae drift downstream for some time before larvae are mature enough to navigate and swim purposefully (Deters et al., 2013;George et al., 2018).Although we cannot confirm the individuals that passed upstream later spawned, the timing of upstream passages we recorded overlaps with spawning events that occurred in previous years for bigheaded carp in the UMR (Camacho et al., 2023;La Hood et al., 2023;Larson et al., 2017) and seasonal trends in upstream movement in the Wabash River (Coulter et al., 2022).Therefore, it is plausible that bigheaded carps completing upstream passage in 2019 and 2020 may have been migrating to spawn upstream from LD 19.Upstream movements related to spawning are particularly relevant for population control of invasive species.
In contrast to the results observed for bigheaded carp, there was no significant difference in upstream passage rates between translocated and non-translocated Common Carp (Cyprinus carpio) in a study on the Mississippi River (Finger et al., 2020).
Upstream-experienced fish may also be more motivated to return upstream if those areas contain higher food availability or preferred habitat.In the UMR, the highest density of bigheaded carp occurs downstream from LD 19, and densities of bigheaded carp generally decrease moving upstream from LD 19 (Broaddus & Lamer, 2022;Larson et al., 2017).The higher rate of dam passage among bigheaded carps initially captured upstream may be partially attributable to those fish seeking to return to areas in which plankton densities are higher, exploiting density-dependent growth patterns across the UMR.
White-spotted Char (Salvelinus leucomaenis) translocated upstream from a dam in southern Hokkaido, Japan, displayed higher growth rates relative to conspecifics downstream from the dam, probably because density-dependent competition was reduced above the dam (Morita et al., 2000).The geomorphology of Pool 19 is very different from Pool 20 in that it is more than twice the length of Pool 20 (75 river km vs. 34 river km, respectively), and is characterized by islands, side channels, backwaters, and impounded areas that provide ample habitat for primary production (thus food availability), flow refuge, and nursery habitat (Bhowmik & Adams, 1986;Jahn et al., 1986;Milde et al., 2017).Pool 20, in contrast, has a steep gradient with few side channels and backwater habitats.Importantly, upstream migration for spawning, favorable feeding, habitat preference, and general homing behavior are not mutually exclusive, and all of these may have contributed to the higher rates of upstream passage for upstreamexperienced bigheaded carp.
The use of translocated fish may also be a useful technique for other river studies involving native or invasive species, particularly for studies that run over relatively short temporal scales (e.g., months).Although this study used invasive species, research on native species indicates downstream translocation can induce upstream movements.In studies of golden perch (Macquaria ambigua; Crook, 2004), shoal bass (Micropterus cataractae; Ingram et al., 2013), and common bream (Abramis brama; Gardner et al., 2015), most individuals displayed upstream movements after downstream translocation.Although some of the fish making upstream passage in our study were not physically translocated but were instead upstream-origin fish that migrated downstream from LD 19 of their own volition, translocating fish downstream of an area of interest may be more likely to provide an increased sample size or redetection of fish to inform study questions in a shorter time period.Of 72 translocated upstream-origin bigheaded carp, 17 (24%) made upstream passage during the 2 years of this study, a rate substantially higher than any other group of bigheaded carp in our study (Table 2).The higher rates of upstream passage we observed may be characteristic of translocated fish in general and, if so, indicates the benefit of increased sample size and passages may outweigh the logistical challenges associated with translocation.
Understanding the factors motivating invasive fishes to move through river systems is an important aspect of management efforts to control their populations.We observed strong differences in the upstream passage in upstream-experienced fish relative to those without known upstream experience, including a notable seasonal pattern to such movement, which may characterize bigheaded carp movement in other regions.There is interest in using deterrents to impede bigheaded carp upstream passage at bottleneck dams (e.g., LD 19 on the Mississippi River and Barkley Lock and Dam on the Cumberland River), which has led to a need to develop protocols for evaluating deterrent efficacy.Evaluations of deterrents, particularly those designed to deter bigheaded carps, may benefit from using upstreamexperienced fishes.Aside from simply facilitating the number of fish encounters and observations when evaluating deterrents, the use of translocated fish may also provide the best conservative estimate for deterrent effectiveness.Resource managers could consider translocated fish as a worst-case scenario proxy for fish that are naturally motivated to move upstream.Deterrents that disrupt motivated fish from moving upstream would also be expected to deter less motivated fish from moving upstream, such as those originating downstream from the deterrent.
Ongoing efforts to limit ecological and economic disruption from bigheaded carps requires a variety of techniques (e.g., Cupp et al., 2021), and understanding bigheaded carp behavior is an important aspect of such efforts.This study provides strong evidence for the use of experimental translocation of upstream-experienced bigheaded carp as a population for evaluating deterrents at bottleneck dams because they exhibit such consistently high upstream passage rates relative to bigheaded carp originally tagged downstream from LD 19.The observations we made in this study also provide insight into movement patterns of bigheaded carps in large river systems, which may be characteristic of migration patterns elsewhere.The two drivers that seem most likely to explain the increased drive to move upstream (spawning and feeding) are general characteristics of bigheaded carp biology, and as such, may be expected to transfer to other large river locations.Together with other acoustic telemetry studies of bigheaded carps (e.g., Coulter et al., 2022;Vallazza et al., 2021), this study helps to advance our understanding of invasive fish movements in large rivers.

F
I G U R E 1 Location of Lock and Dam 19 of the Mississippi River near Keokuk, Iowa.Pool 19 is located upstream of Lock and Dam 19 and extends up to the tailwaters of Lock and Dam 18. Pool 20 is located downstream from Lock and Dam 19 and extends downstream to Lock and Dam 20.The blue arrow indicates the direction of flow.Telemetry-receiver array is depicted in orange and labeled by the three main zones: downstream lock approach, lock chamber, and upstream lock approach.[Color figure can be viewed at wileyonlinelibrary.com] Flooding and high water levels in the Mississippi River during May and June 2019 created unsafe conditions for river traffic and required many navigation locks to close for periods of time.Lock and Dam 19 was closed to all traffic from 1 May 1 to 16 May and from 20 May to 16 June of 2019.

Fish
transport tanks were equipped with pure oxygen canisters and airstone infusers for oxygen injection.Duration of transport ranged from 10 to 60 min based on the distance between the collection point and the surgical station.At the surgery location downstream from LD 19 in Pool 20, fish were transferred from the transportation hauling tanks to large holding tanks (750 L) with continuous flow-through of river water.Fish holding time at the surgery location prior to surgery did not exceed 30 min.These fish were considered the translocated upstream-origin treatment group.Bigheaded carp captured, tagged, and released upstream from LD 19 during previous tagging operations in 2016-2019 were included as a separate treatment group with known upstream experience in the experimental design, referred to as the upstream-origin treatment group.These fish were part of other research projects in the UMR (e.g., Fritts et al., 2021; Vallazza et al., 2021).Fish were not physically translocated, but some individuals passed downstream into Pool 20 of their own volition and were available to make upstream passage during the study period.Our sample of fish with known upstream experience upstream from LD 19, therefore, consisted of both fish captured upstream from LD 19 and experimentally translocated downstream to Pool 20 and fish that were captured upstream from LD 19 and moved downstream of their own volition.Bigheaded carp captured, tagged, and released downstream from LD 19 in Pool 20 during this study and during tagging operations in 2015-2018 were included as the treatment group with no known upstream experience in the experimental design, referred to as the downstream-origin treatment group.We used electrofishing and gill nets to capture bigheaded carp in Pool 20, downstream from LD 19.These fish were placed into a standard holding tank (375 L) on a boat containing river water and handled similarly to those captured upstream.Some fish captured from Pool 20 may have had previous experience upstream from LD 19 prior to tagging, but we had no information about their movement history prior to their capture in Pool 20.Surgical implantation of acoustic transmitters for bigheaded carp from Pool 19 and Pool 20 followed by Lubejko et al. (2017) with minor modifications.Fish were tagged with 69-kHz acoustic transmitters (Innovasea, model V16-4H or V16-6H, with ping rates of 30-90 and 80-160 s).Transmitters were tested to ensure proper functionality and soaked for ≥2 min in an alcohol solution prior to surgical implantation.A 2-3-cm ventral incision was made posterior to the pelvic fins of the fish and closed with three interrupted sutures (3-0 Ethilon non-absorbable, black monofilament [669H], Ethicon Inc., We conducted range tests to validate receiver detection efficiency using transmitters with a 7-s fixed interval plus a 3-s transmission period.The detection rate = number of observed detections/number of expected detections * 100, where the number of expected detections is calculated from the known delay between tag transmission and the duration of the test(Kim & Mandrak, 2016).Range testing was conducted in April, June, and December of 2019, but was not conducted during 2020 because of COVID-19 travel restrictions.The average detection rate of available transmissions (± Standard Error [SE]) was 71 ± 4% for receivers in the downstream lock approach, 81 ± 5% for receivers in the lock chamber, and 82 ± 7% for receivers in the upstream lock approach.Data were also incorporated from the UMR large-scale longitudinal receiver array (850 river km) that is maintained by the U.S. Fish and Wildlife Service, Missouri Department of Conservation, and U.S. Geological Survey to detect fish movement across dams in Pools 5A-26 of the Mississippi River.
initially captured upstream from LD 19, 29 were experimentally translocated downstream from LD 19 in May 2019, and the remaining 25 were originally captured, tagged, and released upstream from LD 19 but moved downstream from LD 19 of their own volition after being released.There were 31 upstream passages through the lock chamber during our study, completed by 29 bigheaded carp.Two fish passed upstream in both 2019 and 2020, and the remaining 27 fish passed upstream in only 1 year.All upstream passages were completed by upstream-experienced bigheaded carp (i.e., upstream-origin or translocated upstream-origin individuals).No downstream-origin Upstream−Origin bigheaded carp made upstream passage through the lock chamber during our study.Upstream-experienced fish made upstream passage through the lock chamber at a significantly higher rate than downstream-origin bigheaded carp (χ 2 = 38.4,p < 0.001, df = 1).Of the 54 upstream-experienced bigheaded carp detected downstream from LD 19 from 2019 to 2020, translocated upstream-origin big- Monthly totals of number of bigheaded carp among the three treatment groups detected downstream of Mississippi River Lock and Dam 19 in 2019 (b) and 2020 (d) and monthly upstream passages in 2019 (a) and 2020 (c).[Color figure can be viewed at wileyonlinelibrary.com] length was approximately double that of a fish in the 25th percentile in both groups of Silver Carp (0.29 vs. 0.59 for all Silver Carp detected downstream from LD 19 and 0.37 vs. 0.74 for translocated upstreamorigin Silver Carp).
Total lengths of Silver Carp (Hypophthalmichthys molitrix) tagged in 2019 and detected below Lock and Dam 19, comparing translocated upstream-origin Silver Carp with downstream-origin Pool 20 Silver Carp.(No upstream-origin Silver Carp were tagged in 2019; therefore, this treatment group is not included in this analysis.)Fish that completed the upstream passage are denoted with blue circles.[Color figure can be viewed at wileyonlinelibrary.com] T A B L E 2 Number of bigheaded carp active transmitters released by partner agencies in Mississippi River Pool 16 to Pool 20 (i.e., the number of tagged fish released from 2016 to 2019), number of transmitters detected in the downstream lock approach of Lock and Dam 19(LD 19)during this study, and the number of bigheaded carp making upstream passages during this study by their group/origin.