Journal of Great Lakes Research 37 (2011) 54–60

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Journal of Great Lakes Research

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Movement patterns and habitat characteristics of Lake Sturgeon(Acipenser fulvescens) in the St. Marys River, Michigan, 2007–2008

Brandon Gerig a,1, Ashley Moerke a,⁎, Roger Greil a, Scott Koproski b

a Aquatic Research Laboratory, Lake Superior State University, 650 W. Easterday Ave, Sault Ste. Marie, MI 49783, USAb United States Fish and Wildlife Service, Alpena National Fish and Wildlife Conservation Office, 145 Water Street, Federal Building Rm. 204, Alpena, MI 49707, USA

⁎ Corresponding author.E-mail addresses: bsgerig@ufl.edu (B. Gerig), amoer

rgreil@lssu.edu (R. Greil), scott_koproski@fws.gov (S. K1 Current address: Department of Wildlife Ecology a

Florida, 110 Newins-Ziegler Hall, PO Box 110430, Gaine

0380-1330/$ – see front matter © 2010 International Adoi:10.1016/j.jglr.2010.09.007

a b s t r a c t

a r t i c l e i n f o

Article history:Received 30 June 2009Accepted 11 February 2010Available online 20 October 2010

Communicated by R. Marshall Werner

Index words:Lake sturgeonSt. Marys RiverTelemetryAcipenser fulvescens

Historically, the St. Marys River (SMR), Michigan, provided suitable habitat for lake sturgeon (Acipenserfulvescens) but their population declined dramatically during the past century due to overharvest and habitatalteration. Since 2000, the Lake Superior State University Aquatic Research Lab has monitored a remnantpopulation of lake sturgeon in the SMR. During 2007 and 2008, lake sturgeon were implanted with sonictransponders to determine spatial extent, movement patterns, and habitat use in the SMR. Telemetryobservations indicated that lake sturgeon inhabit a 40 km river reach, representing approximately one-thirdof the total area of the SMR. Lake sturgeon movement in the SMR was confined to an area between the NorthChannel of Sugar Island to the southern end of East Neebish Island, with the majority centered around thenorth end of Lake George. Additionally, lake sturgeon were not observed in the main shipping channel whichsuggests that they may actively avoid areas with high shipping traffic. During this study, individual weeklymovement rates of lake sturgeon varied from under 100 m to over 25 km. Lake sturgeon used transition areasbetween lotic and lentic waters extensively. These areas create depositional habitats that may be essentialforaging areas for lake sturgeon in the SMR. Telemetry results to date have not confirmed the spawninglocation of lake sturgeon within the SMR. However, two females with partially mature eggs were tagged in2007 andmay spawn within the next 2 years. Their movements could lead to the positive identification of thespawning location which would provide essential information for fisheries managers in the SMR.

© 2010 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

Introduction

The lake sturgeon (Acipenser fulvescens) is a large, long livedpotamodromous fish endemic to the Great Lakes basin (Harkness andDymond, 1961; Scott and Crossman, 1973). Regular migrationsassociated with spawning and smaller movements associated withfeeding have been observed in lake sturgeon, as well as other sturgeonspecies worldwide (Beamesderfer and Farr, 1997). Typically, lakesturgeon undergo migrations from lakes or large rivers to smallertributaries to spawn in the spring (Fortin et al., 1993; Auer, 1999;Knights et al., 2002; Lallaman et al., 2008). After spawning, lakesturgeon migrate out of these tributary rivers and return to theirrespective lakes and rivers (Auer, 1996). Studies in Lake of theWoods-Rainy Lake, Lake Winnebago, and the St. Lawrence Seaway havedocumented extensivemigrations in lake sturgeon (Fortin et al., 1993;Rusak andMosindy, 1997). Auer (1999) found that lake sturgeon fromthe Sturgeon River, Michigan, were capable of post-spawning move-

ke@lssu.edu (A. Moerke),oproski).nd Conservation, University ofsville, FL 32611-0430, USA.

ssociation for Great Lakes Research

ments exceeding 330 km. In contrast, others have indicated that lakesturgeon may remain in their spawning river for much or all of theyear (Lyons and Kempinger, 1992; Rusak and Mosindy, 1997).

Patterns of movement not associated with spawning migrationsare poorly documented, and it remains unclear if lake sturgeon havedistinct home ranges. Within Wisconsin, a mark-recapture studyrevealed that lake sturgeon in Lake Winnebago migrated extensivelyto spawn but returned to defined home-ranges within the lake(Priegal and Wirth, 1971; Lyons and Kempinger, 1992). Furthermore,Auer (1999) suggested that migrations link spawning locations withdistinct areas used for resting, foraging and over-wintering. Incontrast, lake sturgeon within Black Lake were found to moverandomly and have no defined home range (Hay-Chmielewski,1987). Due to differences in life stage and variation in the physicalhabitats that are used for spawning, resting, foraging and over-wintering, generalities are difficult to make when characterizing lakesturgeon movement patterns (Boase et al., 2004).

The Michigan Department of Natural Resources (MI DNR) in theLake Sturgeon Rehabilitation Strategy lists the identification ofcurrent population status as essential to the recovery of lake sturgeon(Hay-Chmielewski and Whelan, 1997). Specifically, fisheries man-agers must determine patterns of movement, stock origin (i.e.resident or non-resident) and spawning locations to properly assess

. Published by Elsevier B.V. All rights reserved.

55B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60

and manage remnant lake sturgeon populations. Currently, the statusof lake sturgeon within Great Lakes connecting waterways is poorlyunderstood due in part to the low abundance of lake sturgeon and thelogistical challenges (i.e. depth and turbidity) of sampling suchsystems. In contrast to rivers that allow for the visual observation ofsturgeon, Great Lakes connecting waterways necessitate the use ofmark-recapture techniques and telemetry to determine lake sturgeonabundance, distribution and habitat use (Boase et al., 2004). Forinstance, the St. Marys River (SMR, hereafter) located in the EasternUpper Peninsula of Michigan, historically held a population of lakesturgeon. Extensive surveys conducted by the MI DNR from 1975 to1995 found that lake sturgeon abundance was declining and by 1995lake sturgeon were absent from the survey (Fielder and Waybrant,1998). Yet since 2000, the Lake Superior State University AquaticResearch Lab has captured over 230 sturgeon in the SMR, with arecapture rate of approximately 15% during summer assessments(Bauman et al., 2011). Despite the SMR being identified in the MI DNRLake Sturgeon Rehabilitation Strategy as having high suitability forlake sturgeon, little data currently exist on this population. Specifi-cally, knowledge gaps that persist in the SMR include an understand-ing of the spatial distribution, movement patterns, spawning location(s) and habitat use. The goals of this study were to: (1) determine the

Fig. 1. The 40-km study reach from the North Channel of Sugar Island to Munuscong Bay inlocation of the St. Marys River in reference to the upper Great Lakes.

spatial extent of lake sturgeon within the SMR, (2) document inter-annual spring and summer movement patterns of lake sturgeon, and(3) document habitat characteristics of locations where lake sturgeonwere located within the SMR.

Methods

Study site

The SMR is the sole connecting waterway between Lake Superiorand Lake Huron and the largest tributary of Lake Huron (Fig. 1). WaterleavesWhitefish Bay in Lake Superior and travels 112 river kilometersto the Detour Passage in Lake Huron. The SMR is divided into theupper and lower river at river kilometer 22.5 by the SMR Rapids. TheSoo Locks, Edison Sault hydroelectric canal, and the SMR Rapidscompensating works form a barrier that likely limits the movement oflake sturgeon between the upper and lower river. The main riverchannel has been altered extensively to a depth greater than 8 m toallow the passage of commercial freighters between Lake Superiorand Lake Huron. Additionally, the SMR compensating works alter thenatural flow regime and restrict discharge to less than 50% of thehistoric outflow (Bray, 1996). Despite the significant anthropogenic

the St. Marys River. Dotted lines represent the shipping channel. Map inset illustrates

56 B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60

alterations in the SMR, the area from the North Channel of SugarIsland to East Neebish Island continues to support a population of lakesturgeon. Within this reach lake sturgeon have access to tributaryrivers and mainstem areas that would provide suitable spawninghabitat. The study reach, from the North Channel of Sugar Island toEast Neebish Island, was ultimately defined by the area that implantedlake sturgeon inhabited.

Capture and tagging methods

Lake sturgeon were captured via setlines (see Bauman et al., 2011)during the summers of 2006 and 2007 using methods established byThomas and Hass (1999). Twelve lake sturgeon were implanted withsonic transponders (Sonotronics Inc.) in 2006 and six additionalsturgeon were implanted in 2007. Lake sturgeon that were implantedranged between 132 and 160 cm in total length and 12.5 to 29 kg intotal weight (Table 1). The sex of the implanted lake sturgeon wasdetermined by the visual observation of ovaries or testes during thesurgical implantation of sonic transponders. Of the 18 sonic taggedlake sturgeon, 6 were female, 7 were male and 5 did not exhibitmature gonads and were unable to be sexed with confidence. Thesonic transponder was inserted by making a 6- to 8-cm incision intothe ventral surface of the fish near the midline posterior to the pelvicgirdle. The tag was placed within the body cavity and the incision wassutured closed with 10–12 individual stitches. Cyanoacrylate wasapplied along the incision and each individual suture to ensureclosure. Each sonic transponder has a 4-year battery life to enablelong-term tracking of the implanted lake sturgeon.

Tracking methods

During the spring and summer sampling period of 2007 and 2008,sonic telemetry was used to locate implanted sturgeon twice perweek between 0900 and 1500 h. Tracking surveys were conductedoutside of the study reach in the shipping channel, Lake Nicolet,Munuscong Bay and St. Josephs Channel when implanted sturgeonwere not located within the study reach. In February 2009 lakesturgeon were tracked underneath the ice to determine winterlocations. A directional hydrophone with a 1-km detection radius wasemployed to locate individual lake sturgeon. When an implanted lakesturgeon was located, GPS location, water depth and water temper-ature were recorded. All fish locations were entered into Arc GIS® 9.0(ESRI, Inc) for spatial analysis. The spatial tools function within ArcGIS® 9.0 was used to calculate extent of movement and mean weeklymovement rate for individual fish. Extent of movement was calculated

Table 1Biological measurements of 18 lake sturgeon implanted with sonic transponders in the SM

Capture date Sonic tag Floy tag PIT tag

5/18/2006 72 khz (3-3-6-7) 10324 9851200312733895/24/2006 73 khz (5-7-7-6) 10321 9851200312605696/7/2006 70 khz (6-6-6-7) 10315 9851200312209866/13/2006 72 khz (3-5-4-7) 10325 9851200312784176/15/2006 70 khz (4-7-7-8) T-00005 42343D370C6/20/2006 73 khz (4-6-5-6) 10304 9851200312706536/23/2006 71 khz (4-4-4-8) 10302 9851200312794186/28/2006 71 khz (3-6-5-6) 10311 9851200312811396/29/2006 70 khz (4-6-4-7) 10337 9851200312816756/30/2006 71 khz (3-7-4-8) T-00018 42353657367/12/2006 72 khz (3-3-3-7) T-00050 422E0977598/18/2006 73 khz (5-5-8-8) T-00030 46543664496/13/2007 75 khz (4-8-8) 010372 42351934646/13/2007 79 khz (3-3-5-4) 010367 9851200312715056/20/2007 77 khz (6-7-7) 00053 42343F78596/30/2007 76 khz (5-5-5) 010377 42027437507/4/2007 78 khz (6-7-8) 010379 9851200312841317/20/2007 80 khz (3-3-5-5) 010391 985120031261320

as a surrogate of home range because of the lack of winter telemetryobservations. The extent of movement was measured as the distancebetween the most upstream location and the furthest downstreamlocation of each implanted lake sturgeon. Weekly movement rate wascalculated as the linear distance traveled from the beginning to end ofa 7 day period in both 2007 and 2008. Extent of movement andweekly movement rate were measured as the shortest linear distancebetween locations which may underestimate the actual distancetraveled. Linear regression was used to compare mean weeklymovement rate to water temperatures within the river in 2007 and2008. Male mean weekly movement rate was compared to femalemean weekly movement rate using a two tailed t-test. Lake sturgeonthat were not sexed were not included in this analysis.

Habitat

Habitat attributes were measured at sites where lake sturgeonwere located during tracking surveys in August 2007 and 2008. Ateach sample site, a Hydrolab® Quanta or MiniSonde was used tomeasure pH, dissolved oxygen (mg/L) and Specific conductivity (μS/m) approximately 1 m above the river bottom. Water velocity wasmeasured to the nearest 0.01 m/s using a Rickly® hydrologic flowmeter approximately 1 m above the river bottom. Substrate type wasdetermined using a ponar sampler. Substrate was classified using amodified Wentworth Scale into six categories based on visualobservation of silt, sand, clay, gravel, cobble and sand withmacrophytes.

Results

Movement

Lake sturgeon movement within the SMR in 2007 and 2008 wasrestricted to the area between the North Channel of Sugar Island toEast Neebish Island (Fig. 2). However, five implanted lake sturgeonwent undetected for up to 1 month during June of 2007. In 2007,implanted lake sturgeon were detected 333 times and in 2008implanted lake sturgeon were detected 316 times. In 2007, lakesturgeon were more fully distributed throughout the study reachwhen compared to 2008 (Fig. 2). The mean extent of movement oflake sturgeon for implanted lake sturgeon (n=18) in 2007 was13.3 km (SE±2.7). In 2008, the mean extent of movement of lakesturgeon (n=18) was 7.5 km (SE±1.6). The movement patterns anddistribution of lake sturgeon varied between individuals and years(Fig. 3). Certain lake sturgeon were sedentary and rarely moved from

R, MI, 2006–2007.

Total length (cm) Girth (cm) Total weight (kg) Sex

145.7 56.3 29 Unknown142.4 52.5 16.5 Unknown132.8 50.5 13.5 Male132 55 16.5 Male132.1 55.9 17.5 Unknown139.2 52.7 17 Male132.1 N/A 15 Male148.5 54.6 20 Unknown134.6 58.7 18 Male146.5 62.5 24.5 Female133.4 54.4 12.5 Unknown160.7 67 29 Female150 65.5 24 Female143 65 25 Female150.4 57.5 21.5 Male158 65 25.5 Female158.5 58.5 20.5 Male150.5 65.2 25 Female

Fig. 2. Spatial distribution of 18 sonic tagged fish in 2007 (n=333) and 2008 (n=316) in the St. Marys River, MI. White dots represent individual locations of sonic tagged lakesturgeon.

57B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60

their first marked location. For instance, Fish 73: 5-7-7-6 was locatednear the base of Squirrel Island in the northern most portion of LakeGeorge for the entire sampling period in 2007 and 2008. Commonly,this fish exhibited movements of less than 100 m per week. The

Fig. 3. Extent of movement for four sonic tagged lake sturgeon in 2007 and 2008 in the St. Mafrom 12 to 22 in 2008.

extent of movement by Fish 70: 4-6-4-7 was 27 km in 2007. In 2008,this same sturgeon occupied only a 3-km reach of the river around thenorth end of Lake George. In both years, Fish 70: 4-6-4-7 used theinflow of the North Channel of Sugar Island and Lake George

rys River, MI. The number of observations for each fish ranged from 12 to 31 in 2007 and

Table 2Physical habitat parameters of sites occupied by lake sturgeon in August 2007 and 2008in SMR, MI.

Current velocity(m/s)

Depth(m)

pH DO(mg/L)

Specific conductivity(μS/m)

2007Mean 0.23 6.11 7.75 8.72 NAMinimum 0.04 1.43 7.41 8.02 NAMaximum 0.43 16.15 7.98 9.25 NA

2008Mean 0.35 6.21 8.18 8.44 105.13Minimum 0.11 2.10 7.96 7.83 95.20Maximum 0.58 14.42 8.40 8.75 107.20

58 B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60

extensively. Fish 71: 3-7-4-8 moved throughout the study area in2007 while in 2008, the movements of Fish 71: 3-7-4-8 wereconcentrated near the confluence of the North Channel of SugarIsland and Lake George and the outflow of Lake George near EastNeebish Island.

The mean weekly movement rate of lake sturgeon in 2007 was2140 m/week (SE±1116 m) compared to 1357 m/week (SE±678 m)in 2008 (Fig. 4). No significant relationship was found between meanweekly movement rate and water temperature in 2007 (R2=0.0862,PN0.05) and 2008 (R2=0.081, PN0.05). Reductions in movement wereobserved at temperatures above 15 °C in 2007 and 18 °C in 2008. In both2007 and 2008, mean weekly movement rate of female lake sturgeonwas significantly greater thanmeanweeklymovement rate formales in2007 and 2008 (2007: t=2.5, df=62, Pb0.01; 2008: t=3.37, df=52,Pb0.001).

Habitat

Water chemistry parameters varied little among sites where lakesturgeon were located (Table 2). In 2007 (n=36), mean pH was 7.75andmean dissolved oxygenwas 8.02 mg/L. In 2008 (n=20), mean pHwas 8.18, mean dissolved oxygen was 8.44 mg/L, and mean. Specificconductivity was 105.13 μS/m. Lake sturgeon in 2007 (n=69) and2008 (n=54) were found at a mean depth of approximately 6 mwitha range from 1.43 m to 16.15 m (Table 2). In 2007 (n=36), thecurrent velocity at lake sturgeon locations varied between 0.04 m/s to0.43 m/s, whereas in 2008 (n=32) current velocity ranged from0.11 m/s to 0.58 m/s. Lake sturgeon were found over six differentsubstrate types in 2007 (n=34) (Fig. 5). Silt and sand were thepredominant substrate types and accounted for 47% and 21% of theobservations, respectively. Gravel and clay substrate types eachaccounted for 12% of the total substrate observations. Lake sturgeonwere infrequently observed over cobble and sand with aquaticmacrophytes. In 2008 (n=30), lake sturgeon occupied similarsubstrates as in 2007 except that they were not located over sandwith macrophytes (Fig. 5). A quantitative assessment of benthicinvertebrates was not conducted, however, ponar samples at loca-tions occupied by sturgeon contained blood worms (Chironomidae),

Fig. 4.Mean weekly movement rate of lake sturgeon andmean weekly water temperature in2/2007 to 8/27/2007. In 2008, weekly movement calculated from 5/27/2008 to 8/19/2008.

burrowing mayflies (Ephemeridae), dragonfly nymphs (Gomphidaeand Macromiidae), small bivalves and crayfish (Orconectes sp.).

Discussion

Movement

The lake sturgeon population monitored in the St. Marys Riverinhabited approximately one-third of the 112-km long river channel,which suggests that the SMR likely holds a resident population of lakesturgeon. The implanted lake sturgeon were primarily found within a40-km reach from the North Channel of Sugar Island to the bottom ofEast Neebish Island. Within the study reach, lake sturgeon used coreareas at the inflowof theNorth Channel of Sugar Island and Lake Georgeand theoutflowof LakeGeorgenear EastNeebish Island. Similarly, catchdata provided by Bauman et al. (2011) found that lake sturgeon in theSMR were only captured between the North Channel of Sugar Island tothe southern end of Lake George. While our telemetry studydemonstrated residency of lake sturgeon during spring and summerin the SMR,wewere unable to conductwinter tracking surveys to verifyyear round residency of implanted sturgeon. However, in February of2009, 10 of 18 tagged lake sturgeon were located through the ice at theinflow of the North Channel of Sugar Island and Lake George, furthersuggesting resident status. Furthermore, preliminary genetic analysis

the St. Marys River, MI in 2007 and 2008. In 2007, weekly movement calculated from 5/

Fig. 5. Percent occurrence of substrate types at sites of sonic tagged lake sturgeon in theSMR, MI, August 2007 (n=34) and 2008 (n=30).

59B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60

suggests that lake sturgeon in the SMR are distinct from other remnantpopulations in Lake Superior and Lake Huron (B. Evans, LSSU,unpublished data). The lack of movement of lake sturgeon in the SMRmay affect metapopulation dynamics by limiting the amount of geneticexchange between the SMR population and other Great Lakes sturgeonpopulations. In the future more research on the seasonality of move-ments and degree of genetic relatedness will provide much neededinformation on how movement and isolation influence lake sturgeonmetapopulation dynamics in the SMR and the Great Lakes.

Similar to lake sturgeon in the SMR, Borkholder et al. (2002) foundthat a population of lake sturgeon in the Kettle River, MN, used only a25-km reach in an unconfined river. Borkholder et al. (2002)hypothesized that the sedentary nature of the population may havebeen a learned behavior in response to a hydroelectric dam that hadbeen present until 1995. Within the SMR, lake sturgeon may beconstrained to the study reach by shipping activities in the shippingchannel and a barrier in the form of the SMR Rapids compensatingworks and the Soo Locks. No tagged lake sturgeon during this studywere located in proximity to the main shipping channel, and previoussetline attempts in the shipping channel were unsuccessful (Baumanet al., 2011). Shipping can impact fish by increasing shear stress,altering water levels, increasing water velocity and increasingturbidity which subsequently alters fish feeding and swimmingbehavior (Wolter and Arlinghaus, 2003). Indirectly, dredging ofshipping channels removes depositional substrates that are importantfor the production of benthic organisms (Allen and Hardy, 1980) thatlake sturgeon feed upon. More study is warranted to determine theextent to which shipping may alter the abundance, survival andbehavior of lake sturgeon in Great Lakes connecting waterways andother large river systems.

While lake sturgeon in the SMR utilized a consistent area from theNorth Channel of Sugar Island to East Neebish Island, individualmovements varied from less than 100 m to over 25 km during a sevenday period. In 2008 lake sturgeon in the SMRmoved on average 700 mless per week than in 2007. Additionally, the largest variation inmovement between years was seen in June when water temperaturesin the SMR were suitable for spawning. Variation in lake sturgeonmovement rates can vary annually as a function of spawningperiodicity and pre-spawning behavior (Auer, 1999). Generally,non-spawning fish inhabit relatively small areas whereas post-spawning fish have been noted to undergo extensive migrations(Fortin et al., 1993; Auer, 1999). This may partially explain why meanweekly movement rate declined from 2007 to 2008. However,extensive migrations greater than 100 km which are characteristicof post-spawning dispersals (Rusak and Mosindy, 1997; Auer, 1999;Knights et al., 2002) were not observed in the SMR.

Past research has indicated that lake sturgeon movement patternscan be influenced by water temperature (Hay-Chmielewski, 1987;

Rusak and Mosindy, 1997; McKinley et al., 1998). Within the SMR nosignificant relationship between movement rate and water temper-ature existed. However, in 2007 lake sturgeon movement rateincreased as water temperatures increased. This movement mayreflect the onset of the spawning migration. Similarly, in the spring inBlack Lake, MI, lake sturgeon movement increased as ambient watertemperatures increased (Hay-Chmielewski, 1987). Lake sturgeonmovement in the SMR was reduced at temperatures exceeding15 °C in 2007 and 18 °C in 2008. Decreased movement in lakesturgeon at increased temperatures may be due to physiologicalstress. McKinley et al. (1998) reported that the locomotor activity oflake sturgeon was reduced and hemorrhaging around the eyes andfins occurred as water temperature reached 19 °C. Hemorrhaging wasnot noted in the SMR. However, decreased activity and an increase inthe prevalence of the ectoparasite Argulus sp. were seen attemperatures above 20 °C in mid-August of 2007 (A. Moerke, LakeSuperior State University, unpublished data).

Within the SMR, movement of implanted female lake sturgeonwas significantly greater than that of male implanted lake sturgeon.In contrast, Auer (1999) found that there were no notabledifferences in male versus female lake sturgeon movement in theSturgeon River, Michigan. Lake sturgeon tagged in the SMR varied inlife stage attributes including age, reproductive state and sex, whichresults in variability in spawning periodicity and sexual maturity(Lyons and Kempinger, 1992; Auer, 1999). In Auer (1999) all lakesturgeon were mature, post spawning fish. Therefore, much of thevariation caused by differences in life stage attributes was reduced.This may explain in part the variation in movement between sexeswithin the SMR.

Habitat

Patterns of lake sturgeon distribution can be influenced byphysical habitat. In shallow, homogenous systems such as LakeWinnebago and Indian Lake where the mean depth does not exceed6 m, lake sturgeon have shown no depth preference (Priegal andWirth, 1971; Bassett, 1982). However, with increased habitatheterogeneity (i.e. variation in depth), lake sturgeon have beenshown to select depths of 6 to 11 m (Hay-Chmielewski, 1987).Similarly, in the SMR, lake sturgeon were found most commonly atdepths around 6 m, although habitat selection of lake sturgeon wasnot measured due to sampling constraints. The SMR offers a diversityof habitats that vary in depth (1 m–25 m), substrate (silt, sand, clay,gravel, cobble, boulder) and water velocity, which may lead to lakesturgeon showing preference for certain areas. Further study isneeded to quantify the level of habitat availability and selection bylake sturgeon in the SMR.

Water velocity may in part determine which habitats lakesturgeon use (Engel, 1990; Knights et al., 2002). All sites usedextensively by lake sturgeon in the SMR were in flowing water.Similarly, lake sturgeon in the Upper Mississippi River used transitionareas (i.e. near impoundments or channel confluences) with moder-ate flow regimes (Knights et al., 2002). Engel (1990) found that lakesturgeon in the St. Croix River used the confluence of a river andriverine lake extensively. This is very similar to the SMR in which thehighest densities of lake sturgeon telemetry observations were foundnear the inflow of the North Channel-Lake George. Depositionalhabitats, such as pools, backwaters and confluences, may providesuitable feeding areas for lake sturgeon (Knights et al., 2002; Thomasand Hass, 2002). Rusak and Mosindy (1997) in the Rainy Riverspeculated that food availability is more important in determininglake sturgeon distribution than microhabitat variables. This indeedmay be true, yet, certain microhabitat variables, such as depth, flowand substrate may facilitate increased secondary production andsubsequently an increased forage base for lake sturgeon.

60 B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60

Spawning site

To date, telemetry data have not identified the spawning site(s) oflake sturgeon in the SMR. In 2007, five implanted lake sturgeon werenot detected for up to 1 month during June. Furthermore, these “lost”sturgeon were not detected during telemetry surveys conductedoutside of the study reach in the shipping channel, Munuscong Bay,and St. Josephs Channel. These individuals may have moved outsidethe study reach to spawn or moved into the Garden River, within thestudy reach, to spawn. Once relocated, all of the “lost” lake sturgeonremained within the study reach.

Anecdotal evidence suggests that the Garden River and EastNeebish Island rapids may be active spawning sites. The Garden RiverFirst Nation (GRFN, hereafter) has reported lake sturgeon sightings inthe Garden River annually during late spring. Furthermore, the GRFNharvests lake sturgeon during the late spring within the Garden River.Additionally, local fishermen have seen lake sturgeon rolling andexhibiting spawning behavior around the East Neebish Island rapids.Both the Garden River and East Neebish Island rapids possesssubstrate whichwould be suitable for spawning and egg development(Lahaye et al., 1992). Additionally, from early June to the end of July,2007 and 2008, lake sturgeon were observed to porpoise and jumpcompletely out of the water at the north end of Lake George and nearEast Neebish Island. In the Lake Winnebago system, lake sturgeonexhibit this jumping behavior approximately 14 days prior to theonset of spawning when water temperatures range from 6 to 16 °C(Bruch and Binkowski, 2002). While these reports provide valuableinsight, empirical evidence of spawning must be obtained. In June of2007, two females with partially mature gonads (eggs) weresurgically implanted with sonic transponders. Hopefully, the move-ments of these fish will lead to the identification of the spawninglocation of lake sturgeon in the SMR in the near future.

Conclusions

Our study combined with Bauman et al. (2011) demonstrates thatthe SMR contains a resident lake sturgeon population that uses a smallspatial area. Due to the relatively small population size (~500;Bauman et al., 2011) and lack of confirmed spawning site, lakesturgeon within the SMR are especially vulnerable to harvest, habitatdegradation and catastrophic events. In the future, research mustidentify the spawning location to understand recruitment dynamics ofSMR lake sturgeon, document the presence of juvenile lake sturgeonin an effort to protect this vulnerable life stage, and examine in greaterdetail the level of genetic differentiation between SMR lake sturgeonand other Great Lakes populations.

Acknowledgments

We are grateful to the Lake Superior State University AquaticResearch Lab summer staff (Scott Collins, Jesse Comben, JoeMenghini,Dan Operhall, Ben Turshack, and Frank Zomer) for their valuableassistance conducting all field work and processing habitat samples,the Bay Mills Indian Community for setline bait and the National Fishand Wildlife Foundation for funding. Additional thanks goes to twoanonymous reviewers for comments and constructive critiques.

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