Hydrological and lock operation conditions associated with paddlefish and bigheaded carp dam passage on a large and small scale in the Upper Mississippi River (Pools 14–18)

Introduction

The movement and dispersal of migratory fish species are important life-history characteristics that can be restricted by natural and artificial structures (Kruk & Penczak, 2003; Zielinski, Voller & Sorensen, 2018). Dams are known to impede fish passage in lotic systems (Porto, McLaughlin & Noakes, 1999; Larinier, 2001; Knights et al., 2002; Zigler et al., 2004). Hydraulic challenges (e.g., velocity, turbulence) and structural impermeability can heavily impact upstream fish passage through dams and reduce connectivity between important feeding and spawning areas (Northcote, 1998; Larinier, 2000; Zielinski, Voller & Sorensen, 2018). Additionally, downstream migration through turbines or spillways may result in significant mortality of fish (Larinier, 2002; Čada et al., 2006). Barriers to passage can create potential implications for long-term population dynamics or in extreme cases, lead to the extirpation of a species or threaten biodiversity (Larinier, 2000; Pess et al., 2008; Liermann et al., 2012).

Although habitat fragmentation may be detrimental to native migratory fish species, impassable barriers can provide an effective, economical tool for controlling harmful and invasive species (Rahel & McLaughlin, 2018; Altenritter et al., 2019). Barriers that lead to fragmented systems can prevent the spread of nonnative species, exotic diseases, and hybridization (Rahel, 2013). Seasonally operated physical and electrical barriers have provided an effective management alternative to control sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes, although they prohibit many non-jumping native fish to pass (McLaughlin et al., 2007; Vélez-Espino et al., 2011). Natural resource managers are faced with balancing the pros and cons of connectivity in aquatic systems (Rahel, 2013; Rahel & McLaughlin, 2018).

The upper Mississippi River (UMR) has been substantially modified over the past century with the construction of a series of 29 navigation locks and dams (LD). Each LD differs in design and the percentage of time in open-river condition, defined as the time when the adjustable spillway gates of the dam (i.e., roller and tainter gates) are raised out of the water, passing unobstructed water through the gates (Wilcox et al., 2004). When the river is at open-river condition, the head and tail surface elevations of the river are nearly equal. Dams that experience frequent open-river condition likely support more upstream fish passage than those that have infrequent or no open-river condition because water velocity through the spillway is reduced compared to controlled conditions (i.e., when partially lowered dam gates create accelerated water velocities and increased turbulence). For example, LDs 1, 2, 14, 15, and 19 are individually at open-river condition less than 2% of the time, or incapable of achieving this condition, likely impeding upstream fish passage during most years (Wilcox et al., 2004). As such, LDs 14, 15, and 19, considered as pinch-point dams, have been identified as focal points for understanding the impact of infrequent open-river condition on native, non-native, and invasive fish passage.

The American paddlefish (Polyodon spathula) is a large-bodied, cartilaginous fish species endemic to the Mississippi River Basin, Gulf Coastal drainages, and historically in the Great Lakes (Eddy & Underhill, 1978; Carlson & Bonislawksy, 1981). Paddlefish were once an abundant species throughout the Mississippi River Basin, but overharvesting, habitat loss and fragmentation, and water pollution have resulted in population declines since the early 1900s (Carlson & Bonislawksy, 1981; Sparrowe, 1986; Unkenholz, 1986; Graham, 1997; Jennings & Zigler, 2000), leading to their classification as endangered, threatened, or a species of concern in several states (Graham, 1997). Paddlefish are highly migratory, capable of travelling great distances in short periods of time (Rosen, Hales & Unkenholz, 1982; Southall, 1982; Russell, 1986; Tripp et al., 2019) but their movement is restricted by the presence of navigation dams (Larinier, 2000; Zigler et al., 2003; Zigler et al., 2004). In the UMR, LDs have the potential to limit paddlefish movement and access to suitable habitats and spawning areas (Zigler et al., 2004). Also, populations of paddlefish might be further threatened by the presence of competing invasive fishes, such as bigheaded carp.

Silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis), hereafter referred to as bigheaded carp, are native to Eastern Asia and are highly invasive in the UMR (Kolar et al., 2007). These fishes have the capability to compete with native planktivores, such as paddlefish and gizzard shad (Dorosoma cepedianum), for food (Schrank, Guy & Fairchild, 2003; Sampson, Chick & Pegg, 2009). Bigheaded carp are highly mobile and since their introduction into the United States in the 1970s (Koel, Irons & Ratcliff, 2000; Kolar et al., 2007), their range and abundance has expanded, thus increasing their potential for causing ecological and economic damage (Kolar et al., 2007). Bigheaded carp can pass upstream through the gated portions of navigation dams (Tripp et al., 2014), as well as through lock chambers of navigation dams (Lubejko et al., 2017; Fritts et al., 2021). Understanding the environmental conditions and fish behaviors associated with dam passage is critical for informing controls to limit the upstream spread of bigheaded carp in the UMR (Lubejko et al., 2017).

UMR dams with attributes that make them more restrictive to upstream fish passage (e.g., infrequent open-river condition, high vertical lift, challenging spillway design features) are considered focal points for fish passage and bigheaded carp management (Wilcox et al., 2004; Upper Mississippi River Asian Carp Partnership, 2018). Although there is potential for improving native fish passage at these pinch-points, these dams are also candidates for placement of deterrent technologies and gate manipulation to further limit the upstream movement of invasive bigheaded carp (Zielinski, Voller & Sorensen, 2018; Finger et al., 2020). Numerous behavioral deterrents are being designed and tested for restricting bigheaded carp movements including acoustic, carbon dioxide, electricity, and multi-sensory deterrents (e.g., Ruebush et al., 2012; Vetter et al., 2015; Cupp et al., 2016; Parker et al., 2016; Dennis, Zielinski & Sorensen, 2019). Understanding the movement of native and nonnative migratory fishes through locks and dams prior to deterrent operation is important. For this reason, paddlefish and bigheaded carp were chosen as representative species for study at strategic locks and dams in the UMR (i.e., locks and dams near the invasion front for bigheaded carp) to inform future decisions regarding deterrents.

The objectives of this study were to better understand large- and small-scale movements and behaviors of paddlefish and bigheaded carp by (1) identifying and describing environmental factors that might be influencing the passage of paddlefish through LDs 14–18, (2) evaluating the effects of environmental variables and lock operation on the presence of bigheaded carp and paddlefish in the downstream approach of LD 15, (3) distinguishing diel and seasonal patterns of bigheaded carp and paddlefish residency in the downstream lock approach of LD 15, and (4) identifying the relations between fish passages through the LD 15 lock chamber with lock operations for paddlefish and bigheaded carp. This information can be used for modeling movement and inform the design and implementation of deterrent technologies to assist managers in restricting bigheaded carp movement while minimizing impacts on native fish passage through UMR LDs.

Materials & Methods

Study area

The study area included a 191-km reach from Pools 14 to 19 (Fig. 1). The study focused on three major pinch-point dams within this reach: LD 14 (river kilometer [rkm] 483), 15 (rkm 482), and 19 (rkm 364). Lock and Dam 14 is constructed of 13 tainter gates and four roller gates, a main lock, and an auxiliary lock for recreational vessels (U.S. Army Corps of Engineers, 2018a). Lock and Dam 15 is constructed of 11 roller gates and two locks, with a main and an auxiliary lock. There is also a hydropower dam located in a secondary channel on the east side of Arsenal Island. These dams are located approximately 2.4 km upstream of LD 15 on either side of Sylvan Island in Sylvan Slough (U.S. Army Corps of Engineers, 2018b). Locks and Dams 14 and 15 are infrequently at open-river condition and are only free-flowing between 1 and 2% of the year on average (Wilcox et al., 2004; Bouska, 2021). Lock and Dam 19 is a high-head hydroelectric dam and the dam gates have never been at open-river condition (Wilcox et al., 2004). Lock and Dam 19 is considered a major impediment to fish movement because all upstream passage is restricted to the lock chamber.

Stationary and manual tracking

An extensive array of stationary receivers (VEMCO VR2W, VR2C, VR2Tx) was used to monitor the movement of tagged fishes. Tagged fish were manually tracked with a mobile receiver (VEMCO Model VR100) and portable omni-directional hydrophone (VEMCO Model VH165; 50–85 kHz) to supplement the passive receiver array and obtain movement and habitat information of bigheaded carp and paddlefish. Manual tracking occurred weekly along a 0.5-km pre-determined grid within the study reach. At each waypoint, the omni-directional hydrophone was submerged for 100 s to detect presence of tagged fish. When a tag was identified, a VEMCO VH110 directional hydrophone (50–84 kHz) was used to obtain a more accurate location of the fish.

To improve understanding of passage by the focal species, a fine-scale receiver array composed of 15 stationary VR2Tx receivers was used (Fig. 2). There were 11 receivers in the downstream lock approach, two receivers inside the main lock chamber, and two receivers positioned above LD 15. Receivers were deployed within recessed ladder wells to protect the receivers and minimize collisions with vessels. Placing receivers in ladder wells resulted in some acoustic shadowing (i.e., physical obstruction of sound waves), however testing conducted prior to the study verified receivers were able to detect transmitters throughout the downstream lock approach, lock chamber, and upstream lock approach. Range testing confirmed the ability to reliably detect transmitters upstream and downstream of the LD 15 lock approach, as well as within the LD 15 lock chamber.

In-situ range testing of the LD 15 fine-scale array receivers was conducted with an acoustic test tag (10-s transmission rate) of the same frequency and power of implanted fish transmitters. Range testing determines an approximate maximum range of detection and evaluates the detection efficiency within this range. At LD 15, three distinct zones were monitored to confirm the ability of the fine-scale array to track progression of transmittered fish moving through three lock zones: the downstream lock approach, the lock chamber, and the upstream lock approach. Range testing was performed by lowering the VEMCO test tag 1-m below the water’s surface from a boat as it moved through the three lock zones. The path of the boat was recorded on a GPS unit, which logged a coordinate and timestamp at 1-s intervals. GPS coordinates and associated timestamps were then matched with the corresponding times of test tag detections on the receivers, resulting in the position of the test tag when it was detected. The time of first detection to the time of last detection in each zone was used to calculate the number of expected detections based on transmission rate—it was presumed the first and last detections defined the maximum detection ranges. Detection efficiency was the number of observed detections/number of expected detections × 100 (Kim & Mandrak, 2016). Detection efficiency is not directly related to the efficiency of detecting a fish in either of the three distinct zones. Because fish tags transmit a signal every 30–90 s, detecting only a few transmissions is necessary to confirm if a fish is present in a zone (e.g., if efficiency were 50% with a nominal delay of 60 s, a fish detected in a zone for two minutes would be detected at least once).

Results

The study was conducted from 01 Jan 2017 through 31 Dec 2019. During this period, water temperature ranged from −0.10 to 29.3 °C (mean = 13.0 °C) and hydraulic head ranged from −0.02 to 11.4 m (mean = 2.6 m) between Pools 14–19 (Table S1). During the study, open-river condition occurred at LD 14 7.0% of the time and at LD 15 12.5% of the time; LD 19 does not experience open-river condition (Table S1). Successful paddlefish passage was observed at all dams, with the greatest number of passages occurring at LD 17 (Table 2). At LD 15, where fine-scale passage with the receiver array was evaluated, there were a total of 14,318 tow and vessel lockages from 2017-2019 (Table S2).

Range testing at LD 15 occurred in April 2019 (Fig. S1) and December 2019 (Fig. S2). Testing in April occurred during major flooding and the average detection efficiency in the upstream lock approach, lock chamber, and downstream lock approach was 36%, 92%, and 89%, respectively. In December, the detection efficiency in the upstream lock approach increased considerably to 90%, while detection efficiencies in the other zones were similar to those observed on the previous test date (lock chamber and downstream lock approach were each 91%).

The number of unique individuals detected in the downstream approach at LD 15 varied weekly by paddlefish and bigheaded carp throughout the study period. Bigheaded carp were present in the lock approach during March through September, whereas paddlefish were present during March through November (Fig. 3). Bigheaded carp had the greatest number of residency events during the summer (77%; Table S3). The presence of paddlefish in the LD 15 downstream lock approach showed some seasonality as presence was highest during April and lower during June through November (Fig. 3). Paddlefish had the greatest number of residency events during the spring (55%) and summer (40%) months (Table S3). Bigheaded carp displayed diel patterns in the LD 15 downstream approach with greater proportions of residency events occurring from 02:00 to 09:00 CST (Fig. 4) while paddlefish did not exhibit any distinct diel patterns.

Passage events at LD 15

During the three years of the study, successful upstream and downstream passages of bigheaded carp and paddlefish have been identified through LD 15 using the fine-scale telemetry array receivers and the large-scale longitudinal array. Passages outside of the fine-scale array were presumed to have occurred through the adjustable spillway gates of LD 15. Bigheaded carp had a total of six upstream passages and three downstream passages completed by four individuals (three silver carp and one bighead carp; Fig. 5). All downstream passages occurred through the adjustable spillway gates. Two bigheaded carp upstream passages occurred through the lock chamber and four upstream passages were presumed to have occurred through the adjustable spillway gates. The two upstream passages through the lock chamber were made by one individual (bighead carp, female) over two years, 2017 and 2018. The first passage occurred on 26 July 2017 when this individual entered the lock chamber before the entrance of an upstream-bound commercial tow with six empty barges and exited with the same tow. The second upstream passage occurred on 24 June 2018 when the same individual entered the lock chamber before the entrance of an upstream-bound recreational vessel and exited with the same vessel. The hydraulic head at the dam during the first and second passages through the lock chamber were 0.93 and 1.55 m (i.e., controlled conditions), respectively. This same individual made a third passage upstream in 2019, presumably through the adjustable spillway gates between June and July 2019 while the river was above flood stage and the dam was at open-river condition.

A total of 22 upstream passages and four downstream passages through LD 15 were completed by 21 individual paddlefish (Fig. 5; Table 2). All downstream passages occurred through the dam gates. Two paddlefish upstream passages occurred through the lock chamber and 20 of the upstream passages were presumed to have occurred through the adjustable spillway gates. The upstream passages through the lock chamber were made by two individuals in 2018. The first passage occurred on 20 June 2018, entering the lock chamber with an upstream-bound commercial tow consisting of 15 empty barges and one loaded barge. The fish entered the lock chamber with the first portion of the nine empty barges and exited upstream with the same tow. The second passage occurred on 22 July 2018 and the individual entered the lock chamber with an upstream-bound commercial tow consisting of 16 empty barges and exited upstream with the first cut of nine empty barges. The hydraulic head during these passages were 2.39 and 2.06 m (i.e., controlled condition), respectively.

Nearly all observed upstream passages for bigheaded carp and paddlefish through the adjustable spillway gates occurred during open-river condition when hydraulic head was <0.4 m (22 of 24; Fig. 5). The two passages through the adjustable spillway gates that occurred outside open-river conditions were completed by a bigheaded carp on 13 June 2017 and a paddlefish on 14 September 2018, when hydraulic head was 0.70 m and 1.10 m, respectively. When hydraulic head was approximately 1-m or greater, paddlefish and bigheaded carp opted for upstream passage through the lock chamber more often than the dam gates (five of seven passages). Both bigheaded carp and paddlefish were able to achieve downstream passages during periods when hydraulic head was >1.08 m (± 0.97 m).

Discussion

This study provided large- and fine-scale evaluations of invasive and native fish behaviors including passage at UMR dams. Locks and Dams 14, 15, and 19 are focal locations for fish passage studies as they are three of the most restrictive dams for upstream fish passage in the UMR (Wilcox et al., 2004). These locks and dams have been identified as potential locations for fish deterrent technologies to limit bigheaded carp range expansion in the UMR (Upper Mississippi River Asian Carp Partnership, 2018). Fish passage information for bigheaded carp and native fish species at these dams could be useful for assessing the potential ramifications of a deterrent on both groups. The results of this study advance the current understanding of bigheaded carp and paddlefish passage frequency and timing and how it is related to environmental conditions and lock operations at UMR dams.

Cox’s proportional hazards model for paddlefish dam passage showed differing results for the upstream and downstream models. Water temperature and hydraulic head were important factors to upstream fish passage through Locks and Dams 14–18. The majority (68%) of paddlefish upstream passages occurred in the spring and early summer months. Water temperatures during these months possibly cued spawning behaviors of paddlefish while the low hydraulic head and associated lower current velocities through the adjustable spillway gates at open-river likely offered less resistance to passage for this species compared to controlled conditions (i.e., periods with dam gates lowered) with high hydraulic head. When water temperatures reach 10 °C, paddlefish begin to congregate in deep pools and start moving upstream in the river in search of inundated gravel bars to spawn (Russell, 1986). In addition to water temperature, increased water velocities and turbulence resulting from partially closed dam gates may exceed the swimming performance of paddlefish, resulting in a decreased presence of paddlefish during periods of high hydraulic head. Velocities through the UMR gates have been estimated as low as 0.6 m/s from a physical model study (Markussen & Wilhelms, 1987; Wilcox, 1999). Zigler et al. (2004) found that when hydraulic head was low (<1.0 m), there was a greater opportunity for upstream passage of paddlefish. Although adult paddlefish have morphological differences from other fish species that increase their critical swimming speed (i.e., 0.86 m/s; Wilcox et al., 2004), high hydraulic head could increase stress, energetic costs, and injury (Haro et al., 2004). Downstream passage is likely more easily achieved by paddlefish than upstream passage over these dams (i.e., swimming with the current is less energetically costly), which could explain the absence of significant factors in the regression model.

Bigheaded carp passage similarly is related to water temperature and hydraulic head. Water temperatures likely cue spawning behaviors in the UMR (Vallazza et al., 2021), and previous studies have shown that most upstream passages of bigheaded carp occurred when water temperature was ≥ 17 °C (Larson et al., 2017), and during open-river condition when the hydraulic head was <0.2 m (Tripp et al., 2014; Lubejko et al., 2017). Bighead and silver carp are capable of sustained swimming speeds of >0.98 m/s for >10 min (Hoover, Zielinski & Sorensen, 2017), which is greater than the lowest velocities reported through UMR dam gates (Wilcox, 1999). Yet, bigheaded carp approaching more restrictive dams, like LD 15, may be more likely to use the lock chamber to avoid high current velocities and turbulence below partially closed gates (Vallazza et al., 2021). Downstream passage was not affected by the same constraints as upstream passages as bigheaded carp were able to make downstream migrations during less favorable passage conditions (Vallazza et al., 2021).

Fish passage through the LD 15 lock chamber has been observed to coincide with vessel lockage in this study. Three upstream passages coincided with the upstream-bound lockage of commercial tows and one passage occurred with an upstream-bound recreational vessel. Our results revealed some important differences from a previous study of UMR dam passages via the lock chamber (Fritts et al., 2021). Similar to our results, the authors documented nearly all bigheaded carp and paddlefish initiating upstream passage via the lock chamber coinciding with an upstream lockage of a commercial tow. Unlike the previous study, we documented fish entrance and exit of the lock chamber occurring during the same vessel lockage event, compared to the previously-described multiple vessel lockages required to complete fish passage. Also, we observed fish passage via the lock chamber occurring in conjunction with a recreational vessel lockage, which is novel to our study. Additional observations of passage through the lock chamber are needed to establish a more definitive relation between lock operations, hydraulic conditions, and lock chamber passage of bigheaded carp and paddlefish at LD 15.

The residency duration and presence events in the downstream lock approach at LD 15 differed greatly between bigheaded carp and paddlefish. The longer residency events of paddlefish compared to bigheaded carp are similar to findings by Fritts et al. (2021) at the downstream lock approach of LD 19. Bigheaded carp were present in the lock approach at LD 15 between May–September, whereas paddlefish showed seasonal patterns preferring spring months (April–May). At LD 25 on the UMR, seasonal fish densities in the lock chamber found a similar occurrence of high fish densities occurring during the spring, summer, and fall months and having lower fish densities in the winter (Johnson et al., 2005; Keevin et al., 2005). The ability for bigheaded carp to spawn within a wide range of water temperatures (18–30 °C; Kolar et al., 2007) and exhibit protracted spawning (Schrank & Guy, 2002; Camacho et al., 2020), may cause bigheaded carp to have longer presence in the lock approach as they are able to take advantage of optimal increases in discharge levels even after spring peak discharges (Vallazza et al., 2021). The seasonal differences between presence of bigheaded carp and paddlefish could be exploited by managers, as a deterrent in the lock approach might be most effective for managing bigheaded carp, with minimal impacts to paddlefish, if used during the mid-summer months.

Bigheaded carp residency duration was influenced by the number of recreational vessels moving downstream, water temperature, and season. Propeller strikes, noises, and bubbles from recreational vessels have been shown to increase stress levels in fish, provoking a “flight response” that leads to displacement of fish away from passing boats (Becker et al., 2013). Bigheaded carp residency duration also increased in the spring and summer, relative to the fall, coinciding with months in which water temperatures are suitable to bigheaded carp spawning. Paddlefish residency duration was influenced by water temperature, the number of commercial tows and recreational vessels moving downstream and the number of commercial tows and recreational vessels moving upstream. Studies have shown that in addition to photoperiod and water flow, water temperature is an important spawning cue for paddlefish (Russell, 1986). The optimum range for paddlefish spawning is 10 °C–20 °C, which occurred during April through June in the study (Purkett Jr, 1961; Hubert et al., 1984; Wallus, 1986). As water temperatures increase beyond this range, upstream migrations through dams would likely decrease.

The most important factors for paddlefish presence events were water temperature, hydraulic head, number of commercial tows and recreational vessels moving downstream, number of commercial tows and recreational vessels moving upstream, year, and season. A decrease in paddlefish presence due to downstream-bound commercial tows could be linked to several attributes of the movement and construction of tows. The shear forces, wake, and currents created by a commercial tow operation have been found to have direct and indirect impact on fish assemblages that can lead to injury or mortality of fish (Wolter & Arlinghaus, 2003). Loaded downstream-bound commercial tows have been documented on average to pass 228% of the water volume of the lock through the wheels (i.e., tug propellers), compared to 49% passed on average with unloaded upstream-bound commercial tow (Maynord, 2005). This may cause additional displacement or mortality to fish that enter a lock chamber with a downstream-bound commercial tow leading to avoidance. Barry et al. (2007) documented paddlefish having a strong avoidance for the frequency emitted by commercial tows, finding that paddlefish immediately fled from an approaching tow and did not return until the tow was more than 2-km from the point of interaction. The specialized inner ear ultrastructure of paddlefish might be damaged by the sonic emissions from tows that could elicit an avoidance response (Lovell et al., 2006). Furthermore, Gurgens, Russell & Wilkens (2000) found that the highly developed rostrum of paddlefish can detect and avoid metal objects, suggesting that the large metallic structure of tow hulls and miter gates might elicit an avoidance behavior by paddlefish.

Conclusion

This study provided novel bigheaded carp and paddlefish presence and passage information related to environmental, hydraulic, and lock operations at UMR dams. Additionally, these results can have application to inform paddlefish and bigheaded carp management decisions at dams similar in operation and construction. Although this study adequately captured behaviors and passages of native and invasive species at a pinch-point dam in the UMR, additional considerations should be explored for future studies. This study had a low frequency of bigheaded carp residency events and passages documented from 2017 to 2019. We believe the low detection rates were a function of too few active bigheaded carp tags in the vicinity of LD 15. Deploying additional acoustically tagged bigheaded carp around LD 15 may elicit more challenges and passages at the dam, giving a more robust dataset for analyses. Additionally, future studies should consider incorporating a diversity of native, migratory species with unique sensory capabilities and life histories that would allow researchers to better understand how different species respond to different types of deterrents.

The increasing frequency of flood events in the UMR may limit the effectiveness of deterrents at locations where fish are able to complete upstream passage through the dam gates during periods of elevated discharge. In the past 10 years, the UMR has experienced six major floods (river stage exceeding flood stage at navigation dams) fueled by a combination of spring rainfall and snowmelt (U.S. Army Corps of Engineers, 2020). Current flood events last longer, are less predictable, and occur more frequently than those occurring in the 20th century. Over the past three years, this study has observed the number of open-river days at dams steadily rising (i.e., LD 15 open-river days ranged between four to 108 days between 2017 to 2019 shown in Table S1; Bouska, 2021). The majority of upstream passages through the dam gates occurred during low hydraulic-head periods, typically co-occurring with major flooding. Increased opportunity for native fish passage is generally the goal for river managers, but the prolonged open-river condition and potential for upstream passage of bigheaded carp through the dam gates might create challenges for managers to limit the upstream expansion of invasive carp populations.

In years with infrequent open-river condition, a deterrent placed in the downstream lock approach may assist in meeting the management goal of reducing upstream passage of bigheaded carps. A combination of containment and control measures could provide the most effective tool for managing bigheaded carp in the UMR. The Upper Mississippi River Invasive Carp Team (UMRICT) is an interagency group across five states that is concerned with minimizing the impacts of bigheaded carp in the UMR (Jackson & Runstrom, 2018). Commercial harvest programs, funded through the UMRICT, are aimed at capturing and removing bigheaded carp in the UMR to prevent establishment of incipient populations (Jackson & Runstrom, 2018). Bigheaded carp removal programs at least temporarily reduce populations and may help alleviate the pressure and number of challenge events invasive species elicit at dams. Fish deterrent technologies at pinch-point dams, paired with removal programs, could assist in preventing or reducing the upstream expansion of bigheaded carp in the UMR. Expanding upon information on fish passage at additional pinch-point dams for deterrent deployment, such as LD 14, could be useful if the reproductive front moves upstream past LD 15 (Zielinski & Sorensen, 2021). Lock and Dam 14 is less frequently at open-river condition than LD 15 and could potentially limit bigheaded carp passages through the dam gates during non-flood events. Bigheaded carp expansion beyond LD 14 is a great concern as the next potential pinch point is 145 rkm upstream at LD 11 (Vallazza et al., 2021). Understanding fish behavior at these dams is a critical information need for river managers as they evaluate potential tools or technologies that may assist in slowing or ceasing the upstream expansion of bigheaded carp in the UMR.

Supplemental Information