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Habitat and Movement of Lake Sturgeon in the Upper Mississippi River System, USA a

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Brent C. Knights , Jonathan M. Vallazza , Steven J. Zigler & Michael R. Dewey

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U.S. Geological Survey , Upper Midwest Environmental Sciences Center , 2630 Fanta Reed Road, La Crosse, Wisconsin, 54603, USA Published online: 09 Jan 2011.

To cite this article: Brent C. Knights , Jonathan M. Vallazza , Steven J. Zigler & Michael R. Dewey (2002) Habitat and Movement of Lake Sturgeon in the Upper Mississippi River System, USA, Transactions of the American Fisheries Society, 131:3, 507-522, DOI: 10.1577/1548-8659(2002)1312.0.CO;2 To link to this article: http://dx.doi.org/10.1577/1548-8659(2002)1312.0.CO;2

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Transactions of the American Fisheries Society 131:507–522, 2002 American Fisheries Society 2002

Habitat and Movement of Lake Sturgeon in the Upper Mississippi River System, USA BRENT C. KNIGHTS,* JONATHAN M. VALLAZZA, STEVEN J. ZIGLER, MICHAEL R. DEWEY

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U.S. Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road, La Crosse, Wisconsin 54603, USA Abstract.—Lake sturgeon Acipenser fluvescens, which are now protected from harvest, are considered rare in the upper Mississippi River and little information is available on the remaining populations. Transmitters were implanted into 31 lake sturgeon from two sites in the upper Mississippi River to describe their habitats and movement. The areas surrounding the tagging sites were core areas for both groups of lake sturgeon based on the high use (about 50% of locations by group) and frequent return to these areas by many of the tagged fish. Core areas contained sites with unique hydraulic characteristics, such that depositional substrates were common yet flow was present; these areas probably provide important feeding habitat for lake sturgeon. Minimal geographical overlap in range occurred between groups, suggesting that river reaches and associated core areas were unique to groups or substocks of fish. Lake sturgeon exhibited complex movement behaviors and had ranges of 3–198 km (median, 56 km) during the study. Tagged fish moved both downstream and upstream through upper Mississippi River navigation dams. However, dams appeared to be intermittent barriers to upstream passage because upstream passage events (10 fish, 19 passages) were fewer than downstream events (13 fish, 35 passages). Extensive use of the Wisconsin River by one group of lake sturgeon tagged in the upper Mississippi River has implications regarding management of a threatened population that transcends regulatory boundaries. Our study indicates that lake sturgeon in the upper Mississippi River system share many movement and habitat use characteristics with populations in other systems. However, significant data gaps preclude development of cogent management strategies, including information on population numbers and dynamics, identification of spawning areas, relations between groups, and assessment of the effects of commercial navigation.

The lake sturgeon Acipenser fulvescens is threatened in 20 U.S. states and 7 Canadian provinces, mainly because of overfishing in the last century, destruction or modification of this species’s habitat, and loss of range (Williams et al. 1989). Historically, lake sturgeon populations declined precipitously in the upper Mississippi River (i.e., the reach of the Mississippi River between St. Paul, Minnesota, and Cairo, Illinois), resulting in a 97% reduction in reported harvest from 1894 (113,000 kg) to 1922 (3,000 kg; Carlander 1954). By 1931, the reported harvest of lake sturgeon was zero. The initial decline probably was caused by commercial overharvest, a common factor in declines of most other lake sturgeon populations throughout their natural geographic range (Ferguson and Duckworth 1997). Despite current protection from commercial harvest, however, lake sturgeon still are considered uncommon or rare in the upper Mississippi River and are listed as endangered or a

* Corresponding author: [email protected] Received September 14, 2000; accepted November 20, 2001

species of concern by four of five states bordering this reach (Pitlo et al. 1995). Recovery of lake sturgeon populations may be hindered by system modifications, especially those related to the construction of low-head navigation dams on the upper Mississippi River in the 1930s, and the construction of hydroelectric and other industrial-purpose dams on the tributaries. Important lake sturgeon habitats may have been altered by main-stem navigation and tributary dams in the upper Mississippi River system, but data on specific positive and negative effects are lacking. For example, dams may have converted important lotic areas such as spawning habitats into impoundments. Ferguson and Duckworth (1997) considered this type of habitat alteration harmful to lake sturgeon populations in Canada. In contrast, spawning habitat may have been created in the tailwaters of navigation dams and along artificial rock structures (e.g., riprapped shorelines and wing dams) in the upper Mississippi River. Placement of rock and gravel substrates in other systems is thought to have benefited lake sturgeon by creating spawning habitat (Kempinger 1988;

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LaHaye et al. 1992). Also, impoundments created by these dams have low current velocity and soft substrates, which may provide feeding and resting habitat for lake sturgeon. Historical migration routes between feeding and spawning areas for lake sturgeon in the upper Mississippi River system probably have been disrupted by dams. Adult lake sturgeon are known to migrate between feeding areas in large rivers or lakes and spawning areas in tributaries (Fortin et al. 1993; Rusak and Mosindy 1997; Auer 1999). Low-head navigation dams on the main stem of the upper Mississippi River may function as barriers to upstream fish movement except when the difference in water level upstream and downstream of the dam (i.e., head) is less than 0.3 m (J. H. Wlosinski, U.S. Geological Survey, personal communication). As well, many highhead dams on the tributaries of the upper Mississippi River probably block historical migrations of lake sturgeon and isolate groups above and below these dams. Seasonal habitat and movement patterns of lake sturgeon have not been identified or described in the upper Mississippi River system. Information on these factors is critical because site fidelity is considered important to spawning success of lake sturgeon and possibly to feeding and overwinter survival. Successful implementation of many potential restoration strategies such as harvest regulations, identification of vulnerable populations, habitat restoration and enhancement, supplemental stocking, and mitigation of barriers to fish passage will require knowledge of lake sturgeon habitat and movement. Therefore, the objectives of this study were to (1) determine habitat use and selection by two groups of lake sturgeon in the upper Mississippi River and (2) determine the spatial and temporal movement patterns of these fish. Study Area The study area encompassed a 198-km reach of the upper Mississippi River between Lock and Dam 5 (river kilometer [rkm] 1,188, measured from the confluence of the Mississippi and Ohio rivers) and Lock and Dam 10 (rkm 990), and a 146-km reach of the Wisconsin River upstream from its confluence with the Mississippi River to the first dam at Prairie du Sac, Wisconsin (Figure 1). The study reach in the Mississippi River contains seven low-head navigation dams with associated locks and six navigation pools. Each navigation pool is named for the downstream navigation dam (e.g., the reach of river between Lock

and Dam 7 and Lock and Dam 8 is referred to as Pool 8). Generally, upstream portions of navigation pools are riverlike, with braided channels and numerous off-channel areas. Downstream portions of navigation pools generally have a shallow impoundment created by the dam. Impoundments, excluding the navigation channel, constitute 4– 57% of the total water surface of the navigation pools in the study reach. Depths in the navigation channel typically range from 4 to 6 m. Substrates in channels are predominately sand, whereas substrates in off-channel areas consist of silt and silt– sand substrates. The study reach in the Wisconsin River is bounded upstream by a hydroelectric dam that is a complete barrier to fish movement and downstream by the upper Mississippi River (Figure 1). The plunge-pool (2–10 m deep) below the dam spillway is lentic during most of the year but can experience substantial current velocities when water is discharged through the spillway gates during high-water periods. The area below the dam powerhouse has high current velocities, shallow depths, and rock and gravel substrates. The remainder of the 146-km reach is a sinuous braided channel with numerous shifting sand bars. Depths vary from several centimeters to several meters and widths range from 200 to 600 m. Backwater areas are rare in this reach. Substrates in the Wisconsin River are predominately sand with occasional rock and gravel bars, but silt substrates are extremely rare. Methods Lake sturgeon were captured with gill and hoop nets at two sites in the upper Mississippi River (Figure 1) during June through October 1997 and during May 1998. Fork length and weight of each captured fish was determined. Radio or ultrasonic transmitters were implanted into the peritoneal cavity of most of the captured lake sturgeon that weighed 7.0 kg or more (Table 1). Surgical procedures to implant transmitters were based on Summerfelt and Smith (1990). Fish were anesthetized by placing them into a 75 mg/L solution of Finquel. An incision 8–10 cm long was made within 2–3 cm of the midline on the ventral surface of the fish, anterior to the pelvic girdle. Transmitters were inserted through the incision. A shielded-needle technique (modified from Ross and Kleiner 1982) was used to exit the radio antenna through the fish’s body wall. Incisions were closed with two layers of sutures, one continuous layer in the peritoneal lining and a second interrupted layer in


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FIGURE 1.—Map of the 198-km reach of the upper Mississippi River and the 146-km reach of the lower Wisconsin River used by two groups of telemetered lake sturgeon. The solid-line bracket indicates the range of movement for group-1 fish tagged at river kilometer (rkm) 1,173, except for one individual (number 3602) that overlapped in range with group-2 fish. The dashed-line brackets (one for the Mississippi River and one for the Wisconsin River) indicate the range of movement for group-2 fish tagged at rkm 1,022. The abbreviation LD stands for lock and dam; stars indicate tagging sites.

the skin. Radio transmitters (Advanced Telemetry Systems, Inc.; 20 mm diameter; 120 mm long) transmitted in the 49 MHz band, weighed 75–85 g, and had a life expectancy of 250 d. Ultrasonic transmitters (Vemco Ltd.; 15 mm diameter; 90 mm long) transmitted in the 50–63 kHz band, weighed 35 g, and had a life expectancy of 425 d. The presence or absence of eggs was recorded for fish receiving transmitters, but sex was not determined for fish without eggs. All fish were released within 1 h of surgery near the capture site. Capture sites were selected based on prior knowledge of lake sturgeon occurrence. Lake sturgeon tagged at rkm 1,173, in the area immediately above the dam (i.e., impounded area) in Pool 5A (Figure 2), are designated group 1. Lake sturgeon tagged at a second site located downstream, at rkm 1,022, in a large secondary channel in Pool 10, are group 2. Pool 10 joins a major tributary, the

Wisconsin River, presenting a potential spawning habitat for lake sturgeon. Pool 5A does not contain a major tributary confluence; thus, adult lake sturgeon in this pool must move through a main-stem navigation dam to spawn in a major tributary. Alternatively, these fish may spawn in Pool 5A or in other pools in the upper Mississippi River. An attempt to locate all tagged lake sturgeon was made once per week during open-water periods and monthly during ice-covered periods. Tracking was conducted from a boat, hovercraft, or airboat, depending on conditions. Pools and tributaries thought to contain tagged lake sturgeon were searched during daylight hours. If lake sturgeon could not be located in the pools and tributaries that were searched, the search was expanded into other pools and tributaries. The study area was eventually defined by the range of movement of tagged lake sturgeon. Areas outside of this defined

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TABLE 1.—General tagging and tracking information on lake sturgeon tagged in navigation Pool 5A (group 1) and Pool 10 (group 2) of the upper Mississippi River during a biotelemetry study.


Tag Tag number Group type a 3592 3601 3605 3613 3616 3594 3600 3602 3609 3619 3590 3595 3597 3599 3611 3612 3617 3618 3591 3603 3606 0001 3593 0002c 0003c 0004c 0005 0006 3607 3608 3615

1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

B B B B B B B B B B B S S S S S S S S B B R B R R R R R S S S

Fork length (cm) 118 139 114 120 111 120 104 115 128 108 122 112 146 152 119 150 133 111 147 117 113 94 120 97 110 143 129 119 127 133 123

Weight Eggs (kg) present 12.8 20.3 11.4 16.3 9.5 13.5 9.7 14.5 16.4 9.7 13.4 11.3 17.6 26.3 15.3 25.8 17.3 10.1 25.2 12.2 18.7 7.0 13.7 10.7 12.3 21.0 20.8 17.5 15.7 20.2 15.3

No Yes No No No No No No No No No No Yes Yes No Yes No No No b No No No Yes No No No Yes No No Yes No

Date captured

Date of last location

Number of locations

Final status

Aug 28, 1997 Sep 3, 1997 Sep 17, 1997 Sep 17, 1997 Sep 17, 1997 Sep 24, 1997 Sep 24, 1997 Sep 24, 1997 Sep 24, 1997 Sep 24, 1997 Oct 9, 1997 Jun 17, 1997 Jun 17, 1997 Jun 17, 1997 Jun 17, 1997 Jun 17, 1997 Jun 17, 1997 Jun 17, 1997 Jun 18, 1997 Jul 15, 1997 Jul 15, 1997 Oct 23, 1997 Oct 27, 1997 May 29, 1998 May 29, 1998 May 29, 1998 May 29, 1998 May 29, 1998 May 29, 1998 May 29, 1998 May 29, 1998

Dec 2, 1998 Dec 2, 1998 Dec 2, 1998 Dec 2, 1998 Oct 6, 1998 Dec 2, 1998 Dec 3, 1998 Sep 1, 1998 Dec 2, 1998 Oct 6, 1998 Dec 3, 1998 Nov 24, 1998 Sep 9, 1998 Jul 9, 1997 Nov 23, 1998 Oct 16, 1998 Nov 24, 1998 Nov 24, 1998 Apr 14, 1998 Nov 23, 1998 Nov 24, 1998 Nov 24, 1998 Aug 18, 1998 May 29, 1998 Jun 3, 1998 Jun 3, 1998 Nov 23, 1998 Sep 14, 1998 Nov 24, 1998 Nov 24, 1998 Nov 24, 1998

55 43 55 52 42 39 43 39 42 27 47 45 51 3 62 52 53 33 35 56 60 28 23 0 1 1 21 16 23 11 23

At large At large At large At large At large At large At large At large At large Stationary At large At large At large Harvested At large At large At large At large Harvested At large At large At large Dead No contact Dead Stationary At large At large At large At large At large

Area last located Pool 5A Pool 5A Pool 5A Pool 5A Pool 8 Pool 5A Pool 8 Pool 10 Pool 5A Pool 9 Pool 8 Pool 10 Wisconsin Wisconsin Wisconsin Pool 10 Pool 10 Pool 10 Pool 9 Wisconsin Pool 10 Pool 10 Pool 9 Pool 10 Pool 10 Pool 10 Wisconsin Pool 10 Pool 10 Pool 10 Pool 10

River River River

River

River

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S indicates a sonic transmitter, R a radio transmitter, and B both sonic and radio transmitters. This fish had eggs when harvested. c This fish is thought to have died soon after release because of an unresolved oxygen debt accumulated during capture and surgery. b

reach were occasionally searched when tagged fish were missing for extended periods. At locations of tagged lake sturgeon, geographic coordinates were recorded from a global positioning system receiver accurate to within 10 m. Depth was measured to the nearest 0.1 m with an electronic depth sounder. The velocity of the current was measured to the nearest 1 cm/s at 0.3 m above the bottom substrate. Substrate was sampled with a petite (225 cm2 sample area) ponar grab sampler and classified on-site by visual estimation of size (modified from Plumb 1981) into a maximum of two of the following four substrate categories, based on particle diameter of the major constituents: rock (.64 mm), gravel (.2 to 64 mm), sand (0.1–2 mm), or silt (,0.1 mm). If the ponar grab sampler failed to collect a sample after two attempts, the substrate was classified as rock. Lake sturgeon locations also were classified into one of nine aquatic area types (modified from Wilcox

1993): main (navigation) channel, main channel border, tailwater, secondary channel, tertiary channel, contiguous backwater lake, backwater shallow aquatic, impounded, or tributary. The coordinates from fish locations were uploaded into a geographical information system (GIS) database and plotted with ArcView (ESRI, Inc., Redlands, California) on a coverage of aquatic area types (U.S. Geological Survey, unpublished data). The resulting coverages of fish locations and aquatic area types were used to determine temporal and spatial characteristics of movement and habitat use for tagged lake sturgeon. For each lake sturgeon, extent-of-movement (distance between the two locations furthest apart during the study), and distance between sequential locations within each calendar season were measured. Movement variables were measured as the shortest linear distance through water between fish locations and therefore probably underestimated the actual dis-

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FIGURE 2.—Map of the core areas for two groups of telemetered lake sturgeon tagged in the upper Mississippi River. Black circles indicate the locations of telemetered lake sturgeon recorded during the 18-month study; stars indicate tagging sites.

tance traveled. Movement rate (m/d) was determined by dividing the distance between sequential locations by the number of days between locations. Analysis of variance (ANOVA) on log-transformed data, blocked by fish (Zar 1984), was used

to determine whether mean movement rate differed among seasons. Fish were treated as blocks in this analysis because individual movements of a given fish were not independent. Only movement rates determined from fish locations observed 3–11 d


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apart (i.e., intervals possible when fish are located once per work week) were included in the analysis. Tukey’s multiple comparison procedure (Zar 1984) was used to compare movement rates among seasons. The GIS coverages of lake sturgeon locations and aquatic area types were used to determine selection of macrohabitats (i.e., aquatic area types). Habitat use for each lake sturgeon was defined as the percentage of locations that occurred in each of the nine aquatic area types. Habitat availability was defined as the percentage of each aquatic area type (based on coverages of aquatic area type) in the pools used by individual fish. Habitat selection was determined by compositional analysis comparing log-ratio transformed use and availability data for each lake sturgeon with a likelihood ratio test (Aebischer et al. 1993). This analysis also treats fish as blocks because individual locations of a given fish were not independent. Student’s ttests were used to determine whether selection differed between pairs of aquatic area types and to rank the relative use of these types (Aebischer et al. 1993). Given their low availability, tailwater and tertiary channel aquatic area types were combined with main channel and secondary channel, respectively, to reduce the number of habitat classifications, thereby reducing the likelihood of a type II error in the multiple comparisons (Alldredge and Ratti 1986). Results Thirty-one lake sturgeon (11 in group 1; 20 in group 2) weighing 7–26 kg were tagged with transmitters (Table 1). Seven of these fish were females carrying eggs; the remainder presumably included males and females at various stages of sexual maturity, including juveniles. Lake sturgeon did not appear to be affected by the capture and transmitter implant, except for three fish that appeared to die soon after release on May 29, 1998 (Table 1). Stress on these three fish from unresolved oxygen debt, which is common after capture and surgery (Summerfelt and Smith 1990), may have been exacerbated by low concentrations of dissolved oxygen (i.e., 3.9 mg/L) at the capture site. At the end of the study, 24 of the remaining 28 tagged fish were considered to be at large. Two tagged lake sturgeon were harvested during the study by recreational anglers in the Wisconsin River. Also, one fish was found dead downstream of Lock and Dam 9, and the transmitter for another had become stationary (i.e., the fish had died or expelled the transmitter); because those two fish had been tracked

for 10 and 13 months, respectively, their fate probably was not related to capture and surgery. Four of the 31 tagged fish were excluded from movement and habitat selection analyses because they were located three or fewer times during the study (Table 1). The 27 tagged fish that were used in the movement and habitat analyses (11 in group 1; 16 in group 2) were located a total of 1,076 times. Far-ranging movement by tagged fish in short time periods over large reaches of river, combined with gear limitations, prevented us from locating individual fish during some sampling weeks. As a result of variations in the rate of success of locating individual fish, in the removal of fish from the study (e.g., because of death, stationary transmitter, or fish harvest), and in the tagging date, the number of locations per tagged fish included in the movement and habitat analyses ranged from 11 to 62 (Table 1). Core Areas The areas surrounding the tagging sites were found to be core areas for both groups of tagged lake sturgeon, given the extensive use of and frequent return to these areas by many fish. Also, these areas were occupied continuously by tagged lake sturgeon during the study. The core area for group-1 fish included the impounded portion of Pool 5A and the adjacent bend in the main channel (Figure 2); 56% of group-1 fish locations occurred within this core area. One tagged lake sturgeon never was located outside of this core area. Other fish often left and returned to the core area (7 of 11 fish; 21 times) after absences of less than 1 to 9 months. Only three tagged lake sturgeon left the core area and did not return during the remainder of the study (4.5–12 months). Most locations of group-1 fish outside of the core area occurred at boundaries between the main channel and channel border in impounded reaches, large bends in the main channel, tailwaters, secondary channels, and confluences of tributaries. Many of these locations of individual fish occurred in Pool 8 (15% of all group-1 fish observations) over periods of less than 0.5 to 8 months. Other distinct areas in the system were used by multiple group-1 fish but generally for only short durations or by just a few fish. Distinct areas so used included the tailwaters of Lock and Dam 5 in Pool 5A (6 fish; 3% of group-1 observations), a secondary channel in Pool 6 (2 fish; 3% of group-1 observations), and the tailwaters of Lock and Dam 6 in Pool 7 (3 fish; 2% of group-1 observations). The core area for group-2 fish included a sec-



ondary channel of the main-stem river and the confluence with the Wisconsin River; 49% of group2 fish locations occurred within this core area (Figure 2). Fish commonly left and returned to this core area (12 of 16 fish; 16 times) after absences of less than 1 to 12 months. Three fish never were located outside of this core area. Only one tagged lake sturgeon left the core area and did not return during the remainder of the study (4.5 months). Eight of 16 group-2 fish used a 4.5-km reach of the Wisconsin River just downstream of the Prairie du Sac dam (31% of group-2 fish observations). Although used extensively, this reach below the dam was not continuously occupied by tagged lake sturgeon the way the core areas were; all tagged fish left this reach below the dam during spring. Other areas in the upper Mississippi River used by multiple group-2 fish for extended periods included a 4-km reach of the upper Mississippi River below the confluence with a large secondary channel in upper Pool 10 (accounting for 4% of group2 fish locations; 4 fish for ,0.5–4 months) and a 9-km reach of the main channel–channel border in the impounded portion of Pool 9 (accounting for 10% of group-2 observations; 4 fish for 0.5–11 months). Use and Selection of Aquatic Area Types The impounded category was the most frequently used aquatic area type by group-1 fish during all seasons (Figure 3), reflecting the dominant aquatic area type in the core area (Figure 2). Main channel, channel border, and secondary channel aquatic area types received low to moderate use by group-1 fish, depending on season. Tailwaters accounted for about 5–10% of observations by season. Group-1 fish seldom used backwater aquatic area types except during spring, and only one fish was observed in a tributary (i.e., the Wisconsin River). Selection analysis indicated that group-1 lake sturgeon did not select aquatic area types randomly (P , 0.001). Aquatic area types, ranked from most selected to least selected, were impounded, channel border, main channel, secondary channel, backwater lake, and backwater shallow aquatic. Pairwise comparisons indicated that group-1 fish significantly preferred (P , 0.05) impounded and channel border areas relative to backwater aquatic area types. Tributary was the aquatic area type most used by group-2 fish during all seasons except spring (Figure 3), reflecting substantial use of the area downstream of the hydroelectric dam in the Wis-

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consin River and the core area, which included the mouth of the Wisconsin River (Figure 2). Secondary channel, main channel, and channel border were moderately used by group-2 fish during all seasons (Figure 3). Group-2 lake sturgeon seldom used tailwaters in the upper Mississippi River, but frequently used the tailwaters of the hydroelectric dam on the Wisconsin River (8 fish; 10% of group2 fish locations). Group-2 fish seldom were located in backwater or impounded aquatic area types, however, use of these aquatic area types increased somewhat in spring (Figure 3). Selection analysis of aquatic area types in the upper Mississippi River (i.e., tributary excluded) for group-2 lake sturgeon indicated that aquatic area types were not selected randomly (P , 0.001). Aquatic area types ranked from most to least selected by lake sturgeon were secondary channel, main channel, channel border, impounded, backwater shallow aquatic, and backwater lake. Pairwise comparisons indicated that selection of secondary channel, main channel, and channel border was equivalent (P . 0.05), but group-2 fish preferred (P , 0.05) these aquatic area types to the impounded, backwater shallow aquatic, and backwater lake areas. When the Wisconsin River (i.e., tributary) was included in the selection analysis for group-2 lake sturgeon, aquatic area types still were not selected randomly (P , 0.001). Aquatic area types ranked from most selected to least selected were secondary channel, main channel, channel border, tributary, impounded, backwater shallow aquatic, and backwater lake. Pairwise comparisons indicated that selection of secondary channel, main channel, and channel border remained equivalent (P . 0.05) and were preferred (P , 0.05) over impounded, backwater shallow aquatic, and backwater lake types by group-2 fish. Also, secondary channels were preferred by group-2 fish relative to tributaries, and tributaries were preferred relative to impounded, backwater shallow aquatic, and backwater lake aquatic area types. Microhabitat Variables Group-1 lake sturgeon used areas with a wide range of bottom current velocities (range, 0–75 cm/s; median, 13 cm/s) and depths (range, ,1 m to 18.2 m; median, 3.3 m). However, current velocities generally were no more than 40 cm/s at fish locations (Figure 4) and few sturgeon were found where flow was absent. Depths at fish locations generally were 7.0 m or less, depths of 1.0–3.0 m being the most common (Figure 4). Sub-

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FIGURE 3.—Mean seasonal use of aquatic area types by two groups of telemetered lake sturgeon tagged in the upper Mississippi River. Aquatic area types include tailwater (TW), main (navigation) channel (MC), main channel border (CB), secondary channel (SC), impounded (IM), backwater lake (BL), backwater shallow aquatic (BS), and tributary (TB). The symbol N represents the number of fish. Vertical lines represent 1 standard error of the mean.

strates containing silt (i.e., silt and silt–sand) were used extensively by group-1 fish during all seasons (Figure 5). This condition was particularly evident in the core area, where 70% of all locations were over silt-containing substrates. Sand-only substrates also were common at group-1 fish locations during all seasons except spring. In spring, siltcontaining substrates were found at 80% of all

locations. Substrates with rock and gravel rarely were used by group-1 lake sturgeon. Group-2 lake sturgeon locations in the upper Mississippi River (i.e., excluding locations in the Wisconsin River) occurred at a wide range of current velocities (range, 0–74 cm/s; median, 22 cm/ s) and depths (range, ,1–14.6 m; median, 5.4 m). As with group-1 fish, most locations of group-2

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FIGURE 4.—Current velocity and depth at locations of two groups of telemetered lake sturgeon tagged in the upper Mississippi River. Group-2 fish locations were subdivided into two categories, those in the upper Mississippi River and those in the Wisconsin River. Current velocity classes are in increments of 10 cm/s (e.g., 30 indicates 30–39 cm/s). Depth classes are in 1-m increments (e.g., 6 indicates 6.0–6.9 m).

fish in the Mississippi River occurred at current velocities of 40 cm/s, or less; however, current velocities of 10 cm/s or less were less common (Figure 4). In general, group-2 fish in the Missis-

sippi River used areas of greater depth than those used by group-1 fish (Figure 4). Also like group1 fish, group-2 fish in the Mississippi River used substrates containing silt extensively during all

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FIGURE 5.—Seasonal use of substrate types by two groups of telemetered lake sturgeon while in the upper Mississippi River. Substrate types include silt containing, sand only, and rock or gravel containing.

seasons (Figure 5). Within the group-2 core area, 77% of all locations were over silt-containing substrates. Group-2 fish generally used sand-only substrates less frequently than did group-1 fish. Group-2 fish, like group-1 fish, rarely used substrates of rock and gravel in the Mississippi River. At group-2 fish locations in the Wisconsin River, current velocities typically were greater (median,

37 cm/s; Figure 4) than those observed at fish locations in the Mississippi River (median, 22 cm/ s), and substrates were either sand-only or rock and gravel. Movement During the study, group-1 lake sturgeon moved upstream from the tagging site as far as 15 km to

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the tailwaters of Lock and Dam 5 (six fish) and commonly moved downstream as far as 80 km to lower Pool 8 (four fish; Figure 1). No group-1 fish passed upstream through Lock and Dam 5, the first navigation dam upstream of the group-1 tagging site. One individual (number 3602) from group 1 moved as far as 165 km downstream to the middle of Pool 10 (Figure 1). This movement of a single fish was the only overlap in range between group1 and group-2 lake sturgeon observed during the study. Overall, 9 of 11 fish in group 1 moved downstream out of Pool 5A, traversing 5–165 km and passing through 1–5 navigation dams. Three of the nine fish that left Pool 5A never returned; instead, they eventually settled in a downstream pool (i.e., Pool 8). The other six fish that left Pool 5A returned, although some subsequently moved back downstream. These interpool movements spanned weeks to months and occurred during various seasons (e.g., Figure 6a) with no clear spatial or temporal pattern. During interpool movements, group-1 lake sturgeon passed downstream through navigation dams a total of 31 times and upstream through navigation dams 14 times. The median extent of movement for fish in group 1 was 56 km (range, 3–177 km). Group-2 lake sturgeon within the upper Mississippi River moved a maximum of 46 km upstream from the tagging site to the middle of Pool 9 and 31 km downstream to lower Pool 10 (Figure 1). Within the Wisconsin River, group-2 fish moved from the mouth of the river upstream 146 km to the hydroelectric dam at Prairie du Sac. Eight of 16 fish in group 2 moved from Pool 10 in the upper Mississippi River to the area below the Prairie du Sac hydroelectric dam on the Wisconsin River during summer or fall (e.g., Figure 6b). Two individuals made this movement in both years of the study (i.e., 1997 and 1998). All five fish that moved to points near the hydroelectric dam during summer or fall 1997 returned to the Mississippi River during the following spring. Similarly, five fish moved to the area below the Prairie du Sac dam in summer 1998, but the study ended before we could observe any fish that might have returned to the Mississippi River during the following spring. Another movement exhibited by multiple group-2 lake sturgeon was that of four individuals (one individual twice) moving upstream through Lock and Dam 9 to an area in lower Pool 9 about 30 km from the tagging site. These movements occurred in spring (three times) or summer (twice), and the fish remained in Pool 9 for 0.5–11 months (e.g., Figure 6c). During interpool movements, group-2 fish passed

through a single navigation dam (i.e., Lock and Dam 9) a total of nine times (five upstream passages and four downstream passages). The median extent of movement for individual fish in group 2 was 97 km (range, 6–198 km). Mean rates of movement (m/d) for both groups combined (27 fish, 727 movements) differed significantly among seasons (P 5 0.016; Figure 7). Movement rate was significantly greater in spring than in fall (P , 0.05), but summer movement rates did not differ from spring or fall movement rates. Winter was not included in the analysis because observations were few during this season and intervals between locations were generally greater. However, movement rate appeared to be minimal during winter (Figure 7). The frequency of occurrence of movements exceeding 10 km between sequential locations indicated that lake sturgeon typically make these longer movements during spring and summer (56 movements: 20 during spring, 8 transitional, and 28 during summer), rather than fall (11 movements) or winter (2 movements). Four individual fish (one fish twice) exhibited movement rates greater than 10 km/d during the study; these high rates of movement occurred when fish moved between Pool 10 in the upper Mississippi River and the Prairie du Sac dam on the Wisconsin River during spring (two movements) or summer (three movements). The greatest movement rate observed for an individual fish was 17.5 km/d. Discussion The lake sturgeon tagged during our study moved over a large geographic extent, but they frequently returned to and used heavily two core areas. Such core areas may be limited in number and unique to a group or substock of lake sturgeon, with only infrequent exchange of fish between areas. During the 18-month tracking period, only one of our tagged lake sturgeon moved between the two core areas, which were located 150 km apart. Other studies have noted distinct areas of use by groups of lake sturgeon (Fortin et al. 1993; Rusak and Mosindy 1997) and other sturgeon species (Buckley and Kynard 1985; Kieffer and Kynard 1993) within a system. However, the extent to which separate areas of use define stocks or substocks remains unclear. In the St. Lawrence River system, for example, groups of lake sturgeon defined by separate feeding areas shared the same spawning areas simultaneously (Fortin et al. 1993), whereas groups defined by separate wintering areas in the Lake of the Woods–Rainy River


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FIGURE 7.—Mean seasonal movement rate of two groups of telemetered lake sturgeon from the upper Mississippi River. The means for spring, summer, and fall include movement intervals with 3–11 d between fish locations. The mean for winter includes all movement intervals regardless of the interval duration. Vertical lines represent 1 standard error of the mean.

system used the same spawning grounds but at different times (Rusak and Mosindy 1997). In the Lake Winnebago–Wolf River system, groups of lake sturgeon, defined by separate feeding and wintering areas, were thought to use separate spawning grounds (Lyons and Kempinger 1992); however, more recent information indicates that these fish may be from a single population segregated by sexual maturity (Bruch 1999). Core areas and other sites used extensively by lake sturgeon appeared to contain hydraulically similar conditions characterized by transition from high current velocities to slower velocities. These transition areas (e.g., areas in or near impoundments, the confluence of the main channel with large secondary channels or tributaries, and the boundary between the main channel and main channel border in impounded reaches), which are due to local changes in river morphometry, result in depositional substrates (i.e., silt-containing) and probably represent important feeding habitats for lake sturgeon. Engel (1990) reported that lake sturgeon in the St. Croix River heavily used a transitional area between the river and a riverine lake. He speculated that this area may be particularly productive for invertebrates important to lake stur-

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geon as food. Buckley and Kynard (1985) and Kieffer and Kynard (1993) reported that shortnose sturgeon in the Connecticut and Merrimack rivers extensively used areas where the current velocities decreased, including areas at the head of pools created by low-head dams and natural river constrictions, at the head of the tidal influence, and in estuaries. They speculated that these areas provided optimal substrates for the prey of shortnose sturgeon. Identifying feeding habitats for lake sturgeon in the upper Mississippi River is an important step in protecting and restoring the remaining populations. The velocity of the current also may be an important variable in determining lake sturgeon habitat. Although Rusak and Mosindy (1997) suggested that food availability may be more important than other microhabitat variables in determining the distribution of lake sturgeon in the Lake of the Woods–Rainy River system, they noted that water movement (i.e., current) was common at lake sturgeon locations, even within the lake. Similarly, our lake sturgeon avoided silt-laden backwater areas that lacked flow but used a wide range of depths and flows over silt or sand substrates. Use of habitats with flow may ensure that lake sturgeon do not get trapped in seasonally unfavorable areas such as backwaters that experience low dissolved oxygen and high water temperature during summer. Conversely, lake sturgeon may avoid areas with high current velocity because of the increased energy costs and diminished food resources in those areas. This hypothesis is consistent with our observation that the proportions of fish locations over substrates containing silt (i.e., areas with lower current) were greater during spring, when discharge was high, than in other seasons, when discharges were generally lower. Whether these fish were avoiding high current or exploiting food resources, or both, is not known. Movements of tagged lake sturgeon during our study were complex. Many individuals exhibited site fidelity, moving substantial distances away from core areas and then returning weeks or months later. In contrast, some fish left core areas and never returned, whereas others stayed within a core area throughout the study. Also, temporal

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FIGURE 6.—Examples of movements exhibited by individual telemetered lake sturgeon in the upper Mississippi and Wisconsin rivers: (a) group 1, number 3609; (b) group 2, number 3606; and (c) group 2, number 3593. Numbers correspond to the dates on which that fish was observed in each location.


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patterns of movements were not obvious, except for movements of lake sturgeon between the upper Mississippi River and the Wisconsin River. However, these movements were not very synchronous among fish, occurring over periods of weeks or months. Other researchers have noted complex and asynchronous movements of individuals of several sturgeon species, including lake sturgeon, from single populations (Buckley and Kynard 1985; Engel 1990; Rusak and Mosindy 1997). Lake sturgeon are long-lived, late-maturing, and intermittent spawners, such that a population of them probably contains diverse life stages at any given time; as a result, habitat requirements and associated movement patterns vary among individuals (Auer 1996). Furthermore, age at maturity (Roussow 1957) and the spawning interval (Lyons and Kempinger 1992) may differ between male and female lake sturgeon, further complicating migration patterns between sexes. Lake sturgeon tagged in our study varied in size, sex, and reproductive state; this range in life stages probably contributed to the general lack of definitive movement patterns observed, and precluded us from determining sex- or life-stage-specific movement patterns. Most of the navigation dams in our study area were at least intermittently passed by lake sturgeon. However, the disproportionate number of downstream passage events versus upstream passage events suggests that these dams were periodic barriers to upstream movement. Furthermore, the six fish that inhabited the tailwaters of Lock and Dam 5 at various times during the study never passed upstream through that dam, suggesting that it may be a significant barrier. All other navigation dams in which tagged lake sturgeon were observed in the tailwaters were passed by fish moving upstream. Whether or not navigation dams are barriers to spawning migrations of lake sturgeon is unclear, but diminished access to upstream tributaries could adversely affect reproductive success. Identification of spawning areas is a critical data gap for managing lake sturgeon in large river systems, including the upper Mississippi River. We were unable to confirm whether lake sturgeon from the Mississippi River were spawning in tributaries or the main stem. In our study, many lake sturgeon tagged in Pool 10 of the Mississippi River moved into the Wisconsin River during summer and fall and then moved back to the Mississippi River during the following spring, possibly after spawning. Fall migrations to staging areas followed by movements onto the spawning grounds in spring have

been observed for several sturgeon species, including lake sturgeon (Buckley and Kynard 1985; Lyons and Kempinger 1992). Conversely, Pool 5A fish had no obvious fall or spring pattern that would allow us to identify potential spawning migrations. Because movement behaviors exhibited by lake sturgeon are complex, future telemetry studies to identify spawning areas will require large sample sizes and specific data on sex and maturity of the individuals studied. Effective management of lake sturgeon in large river systems that cover broad geographic areas and transcend regulatory boundaries requires information on relations between groups or substocks of fish. Our study demonstrated that lake sturgeon in Pool 10 in the upper Mississippi River and in the lower Wisconsin River are clearly one stock that makes substantial use of both rivers. Lake sturgeon tagged in Pool 10 were moving between areas with different harvest regulations; in the Wisconsin River harvest is allowed for about 6 weeks during fall, whereas no harvest is permitted in the upper Mississippi River. Two of our tagged lake sturgeon, both females carrying eggs, were harvested while in the Wisconsin River. Moreover, our data suggest that the tendency for lake sturgeon to concentrate in a few small areas in the Wisconsin River may increase their vulnerability to harvest. This vulnerability of potential spawners warrants concern, given that the upper Mississippi River population of lake sturgeon is considered threatened. Protection of spawning adults is a vital component of many management strategies for restoring and maintaining lake sturgeon (Fortin et al. 1993; Bruch 1999). The hydroelectric dam at Prairie du Sac marked the boundary for upstream movement in the Wisconsin River by our tagged lake sturgeon. This dam partially isolates the groups of lake sturgeon occurring above and below the dam; historically, these two groups were allowed to mix or constituted a single population. Based on age and growth studies (Larsen 1988) and anecdotal reports, lake sturgeon above the Prairie du Sac dam spawn near the next upstream dam. Larsen (1988) reported that lake sturgeon tagged above the Prairie du Sac dam were recaptured in the upper Mississippi River and that occasionally lake sturgeon were removed from the intake screen of the hydroelectric plant on this dam, suggesting that fish from above the dam may be a source of recruitment for the lake sturgeon population below the dam. The relations between lake sturgeon in the main stem of the upper Mississippi River and those in tributaries require fur-



ther examination to ensure that management strategies protect lake sturgeon systemwide. Restoration of lake sturgeon populations in the upper Mississippi River system will require identification of the factors that are limiting recovery. Our data are a first step in providing basic information on upper Mississippi River lake sturgeon, identifying important habitats within our study area, and evaluating the influence of habitat modifications (e.g., dams and impoundments) on lake sturgeon populations. Our study indicates that lake sturgeon in the upper Mississippi River system share many movement and habitat use characteristics with sturgeon populations in other systems. However, the development of cogent management strategies is impaired by significant data gaps, including ones pertaining to population numbers and dynamics, spawning and nursery areas, relations between groups, and assessment of the effects of commercial navigation. Acknowledgments Funding for this project was provided by the U.S. Geological Survey. We thank Peter Rust, Robert Kennedy, Doug Betz, Melissa Meier, and William Klouda from the Upper Midwest Environmental Sciences Center, U.S. Geological Survey in La Crosse, Wisconsin, for their assistance with data collection and management. Don Valley of Prairie du Chien, Wisconsin, assisted with capturing lake sturgeon. We thank biologists with the U.S. Fish and Wildlife Service Region 3 for their valuable comments on study design. The manuscript was reviewed by Ronald M. Bruch and two anonymous reviewers. References Aebischer, N. J., P. A. Robertson, and R. E. Kenward. 1993. Compositional analysis of habitat use from animal radio-tracking data. Ecology 74:1313–1325. Alldredge, J. R., and J. T. Ratti. 1986. Comparison of some statistical techniques for analysis of resource selection. Journal of Wildlife Management 50:157– 165. Auer, N. A. 1996. Importance of habitat and migration to sturgeons with emphasis on lake sturgeon. Canadian Journal of Fisheries and Aquatic Sciences 53:152–160. Auer, N. A. 1999. Population characteristics and movements of lake sturgeon in the Sturgeon River and Lake Superior. Journal of Great Lakes Research 25: 282–293. Bruch, R. M. 1999. Management of lake sturgeon on the Winnebago system—long term impacts of harvest and regulations on population structure. Journal of Applied Ichthyology 15:142–152.

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Buckley, J., and B. Kynard. 1985. Yearly movements of shortnose sturgeons in the Connecticut River. Transactions of the American Fisheries Society 114: 813–820. Carlander, H. B. 1954. History of fish and fishing in the Upper Mississippi River. Upper Mississippi River Conservation Committee, Rock Island, Illinois. Engel, M. P. 1990. Population parameters of lake sturgeon in the St. Croix River with special reference to movements. Wisconsin Department of Natural Resources, Summary report, Baldwin. Ferguson, M. M., and G. A. Duckworth. 1997. The status and distribution of lake sturgeon, Acipenser fulvescens, in the Canadian provinces of Manitoba, Ontario and Quebec: a genetic perspective. Environmental Biology of Fishes 48:299–309. Fortin, R., J. Mongeau, G. Desjardins, and P. Dumont. 1993. Movements and biological statistics of lake sturgeon populations from the St. Lawrence and Ottawa River system, Quebec. Canadian Journal of Zoology 71:638–650. Kempinger, J. J. 1988. Spawning and early life history of lake sturgeon in the Lake Winnebago system, Wisconsin. Pages 110–122 in R. D. Hoyt, editor. The 11th annual larval fish conference. American Fisheries Society, Symposium 5, Bethesda, Maryland. Kieffer, M. C., and B. Kynard. 1993. Annual movements of shortnose and Atlantic sturgeons in the Merrimack River, Massachusetts. Transactions of the American Fisheries Society 122:1088–1103. LaHaye M., A. Branchaud, M. Gendron, R. Verdon, and R. Fortin. 1992. Reproduction, early life history, and characteristics of the spawning grounds of the lake sturgeon (Acipenser fulvescens) in Des Prairies and L’Assomption rivers, near Montreal, Quebec. Canadian Journal of Zoology 70:1681–1689. Larsen, T. 1988. The lake sturgeon fishery of Lake Wisconsin, 1978–1985. Wisconsin Department of Natural Resources, Fish Management Report 136, Poynette. Lyons, J., and J. J. Kempinger. 1992. Movements of adult lake sturgeon in the Lake Winnebago system. Wisconsin Department of Natural Resources, Research Report 156, Madison. Pitlo, J. Jr., A. Van Vooren, and J. Rasmussen. 1995. Distribution and relative abundance of Upper Mississippi River fishes. Upper Mississippi River Conservation Commission, Rock Island, Illinois. Plumb, R. H. 1981. Procedures for handling and chemical analysis of sediment and water samples. U.S. Army Corps of Engineers, Technical Report EPA/ CE-81-1, Vicksburg, Mississippi. Ross, M. J., and C. F. Kleiner. 1982. Shielded-needle technique for surgical implanting radio-frequency transmitters in fish. Progressive Fish-Culturist 44: 41–43. Roussow, G. 1957. Some considerations concerning sturgeon spawning periodicity. Journal of the Fisheries Research Board of Canada 14:553–572. Rusak, J. A., and T. Mosindy. 1997. Seasonal movements of lake sturgeon in Lake of the Woods and

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and Wildlife Service, Environmental Management Technical Center, Onalaska, Wisconsin. Williams, J. E., J. E. Johnson, D. A. Hendrickson, S. Contreras-Balderas, J. D. Williams, M. NavarroMendoza, D. E. McAllister, and J. E. Deacon. 1989. Fishes of North America endangered, threatened, or of special concern: 1989. Fisheries 14(6):2–20. Zar, J. H. 1984. Biostatistical analysis, 2nd edition. Prentice-Hall, Englewood Cliffs, New Jersey.