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Movement patterns and habitat characteristics of Lake Sturgeon (Acipenser fulvescens) in the St. Marys River, Michigan, 2007–2008
Journal of Great Lakes Research 37 (2011) 54–60
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Journal of Great Lakes Research j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / j g l r
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 b
Aquatic Research Laboratory, Lake Superior State University, 650 W. Easterday Ave, Sault Ste. Marie, MI 49783, USA United States Fish and Wildlife Service, Alpena National Fish and Wildlife Conservation Office, 145 Water Street, Federal Building Rm. 204, Alpena, MI 49707, USA
a r t i c l e
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Article history: Received 30 June 2009 Accepted 11 February 2010 Available online 20 October 2010 Communicated by R. Marshall Werner Index words: Lake sturgeon St. Marys River Telemetry Acipenser fulvescens
a b s t r a c t Historically, the St. Marys River (SMR), Michigan, provided suitable habitat for lake sturgeon (Acipenser fulvescens) but their population declined dramatically during the past century due to overharvest and habitat alteration. Since 2000, the Lake Superior State University Aquatic Research Lab has monitored a remnant population of lake sturgeon in the SMR. During 2007 and 2008, lake sturgeon were implanted with sonic transponders to determine spatial extent, movement patterns, and habitat use in the SMR. Telemetry observations indicated that lake sturgeon inhabit a 40 km river reach, representing approximately one-third of the total area of the SMR. Lake sturgeon movement in the SMR was confined to an area between the North Channel of Sugar Island to the southern end of East Neebish Island, with the majority centered around the north end of Lake George. Additionally, lake sturgeon were not observed in the main shipping channel which suggests that they may actively avoid areas with high shipping traffic. During this study, individual weekly movement rates of lake sturgeon varied from under 100 m to over 25 km. Lake sturgeon used transition areas between lotic and lentic waters extensively. These areas create depositional habitats that may be essential foraging areas for lake sturgeon in the SMR. Telemetry results to date have not confirmed the spawning location of lake sturgeon within the SMR. However, two females with partially mature eggs were tagged in 2007 and may spawn within the next 2 years. Their movements could lead to the positive identification of the spawning 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 lived potamodromous fish endemic to the Great Lakes basin (Harkness and Dymond, 1961; Scott and Crossman, 1973). Regular migrations associated with spawning and smaller movements associated with feeding have been observed in lake sturgeon, as well as other sturgeon species worldwide (Beamesderfer and Farr, 1997). Typically, lake sturgeon undergo migrations from lakes or large rivers to smaller tributaries to spawn in the spring (Fortin et al., 1993; Auer, 1999; Knights et al., 2002; Lallaman et al., 2008). After spawning, lake sturgeon migrate out of these tributary rivers and return to their respective lakes and rivers (Auer, 1996). Studies in Lake of the WoodsRainy Lake, Lake Winnebago, and the St. Lawrence Seaway have documented extensive migrations in lake sturgeon (Fortin et al., 1993; Rusak and Mosindy, 1997). Auer (1999) found that lake sturgeon from the Sturgeon River, Michigan, were capable of post-spawning move-
⁎ Corresponding author. E-mail addresses: bsgerig@ufl.edu (B. Gerig), [email protected] (A. Moerke), [email protected] (R. Greil), [email protected] (S. Koproski). 1 Current address: Department of Wildlife Ecology and Conservation, University of Florida, 110 Newins-Ziegler Hall, PO Box 110430, Gainesville, FL 32611-0430, USA.
ments exceeding 330 km. In contrast, others have indicated that lake sturgeon may remain in their spawning river for much or all of the year (Lyons and Kempinger, 1992; Rusak and Mosindy, 1997). Patterns of movement not associated with spawning migrations are poorly documented, and it remains unclear if lake sturgeon have distinct home ranges. Within Wisconsin, a mark-recapture study revealed that lake sturgeon in Lake Winnebago migrated extensively to 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 with distinct areas used for resting, foraging and over-wintering. In contrast, lake sturgeon within Black Lake were found to move randomly and have no defined home range (Hay-Chmielewski, 1987). Due to differences in life stage and variation in the physical habitats that are used for spawning, resting, foraging and overwintering, generalities are difficult to make when characterizing lake sturgeon movement patterns (Boase et al., 2004). The Michigan Department of Natural Resources (MI DNR) in the Lake Sturgeon Rehabilitation Strategy lists the identification of current population status as essential to the recovery of lake sturgeon (Hay-Chmielewski and Whelan, 1997). Specifically, fisheries managers must determine patterns of movement, stock origin (i.e. resident or non-resident) and spawning locations to properly assess
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and manage remnant lake sturgeon populations. Currently, the status of lake sturgeon within Great Lakes connecting waterways is poorly understood due in part to the low abundance of lake sturgeon and the logistical challenges (i.e. depth and turbidity) of sampling such systems. In contrast to rivers that allow for the visual observation of sturgeon, Great Lakes connecting waterways necessitate the use of mark-recapture techniques and telemetry to determine lake sturgeon abundance, distribution and habitat use (Boase et al., 2004). For instance, the St. Marys River (SMR, hereafter) located in the Eastern Upper Peninsula of Michigan, historically held a population of lake sturgeon. Extensive surveys conducted by the MI DNR from 1975 to 1995 found that lake sturgeon abundance was declining and by 1995 lake sturgeon were absent from the survey (Fielder and Waybrant, 1998). Yet since 2000, the Lake Superior State University Aquatic Research Lab has captured over 230 sturgeon in the SMR, with a recapture rate of approximately 15% during summer assessments (Bauman et al., 2011). Despite the SMR being identified in the MI DNR Lake Sturgeon Rehabilitation Strategy as having high suitability for lake sturgeon, little data currently exist on this population. Specifically, knowledge gaps that persist in the SMR include an understanding of the spatial distribution, movement patterns, spawning location (s) and habitat use. The goals of this study were to: (1) determine the
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spatial extent of lake sturgeon within the SMR, (2) document interannual spring and summer movement patterns of lake sturgeon, and (3) document habitat characteristics of locations where lake sturgeon were located within the SMR. Methods Study site The SMR is the sole connecting waterway between Lake Superior and Lake Huron and the largest tributary of Lake Huron (Fig. 1). Water leaves Whitefish Bay in Lake Superior and travels 112 river kilometers to the Detour Passage in Lake Huron. The SMR is divided into the upper and lower river at river kilometer 22.5 by the SMR Rapids. The Soo Locks, Edison Sault hydroelectric canal, and the SMR Rapids compensating works form a barrier that likely limits the movement of lake sturgeon between the upper and lower river. The main river channel has been altered extensively to a depth greater than 8 m to allow the passage of commercial freighters between Lake Superior and Lake Huron. Additionally, the SMR compensating works alter the natural flow regime and restrict discharge to less than 50% of the historic outflow (Bray, 1996). Despite the significant anthropogenic
Fig. 1. The 40-km study reach from the North Channel of Sugar Island to Munuscong Bay in the St. Marys River. Dotted lines represent the shipping channel. Map inset illustrates location of the St. Marys River in reference to the upper Great Lakes.
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alterations in the SMR, the area from the North Channel of Sugar Island to East Neebish Island continues to support a population of lake sturgeon. Within this reach lake sturgeon have access to tributary rivers and mainstem areas that would provide suitable spawning habitat. The study reach, from the North Channel of Sugar Island to East Neebish Island, was ultimately defined by the area that implanted lake 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 by Thomas and Hass (1999). Twelve lake sturgeon were implanted with sonic transponders (Sonotronics Inc.) in 2006 and six additional sturgeon were implanted in 2007. Lake sturgeon that were implanted ranged between 132 and 160 cm in total length and 12.5 to 29 kg in total weight (Table 1). The sex of the implanted lake sturgeon was determined by the visual observation of ovaries or testes during the surgical implantation of sonic transponders. Of the 18 sonic tagged lake sturgeon, 6 were female, 7 were male and 5 did not exhibit mature gonads and were unable to be sexed with confidence. The sonic transponder was inserted by making a 6- to 8-cm incision into the ventral surface of the fish near the midline posterior to the pelvic girdle. The tag was placed within the body cavity and the incision was sutured closed with 10–12 individual stitches. Cyanoacrylate was applied along the incision and each individual suture to ensure closure. Each sonic transponder has a 4-year battery life to enable long-term tracking of the implanted lake sturgeon.
as a surrogate of home range because of the lack of winter telemetry observations. The extent of movement was measured as the distance between the most upstream location and the furthest downstream location of each implanted lake sturgeon. Weekly movement rate was calculated as the linear distance traveled from the beginning to end of a 7 day period in both 2007 and 2008. Extent of movement and weekly movement rate were measured as the shortest linear distance between locations which may underestimate the actual distance traveled. Linear regression was used to compare mean weekly movement rate to water temperatures within the river in 2007 and 2008. Male mean weekly movement rate was compared to female mean weekly movement rate using a two tailed t-test. Lake sturgeon that were not sexed were not included in this analysis. Habitat Habitat attributes were measured at sites where lake sturgeon were located during tracking surveys in August 2007 and 2008. At each sample site, a Hydrolab® Quanta or MiniSonde was used to measure pH, dissolved oxygen (mg/L) and Specific conductivity (μS/ m) approximately 1 m above the river bottom. Water velocity was measured to the nearest 0.01 m/s using a Rickly® hydrologic flow meter approximately 1 m above the river bottom. Substrate type was determined using a ponar sampler. Substrate was classified using a modified Wentworth Scale into six categories based on visual observation of silt, sand, clay, gravel, cobble and sand with macrophytes. Results
Tracking methods Movement During the spring and summer sampling period of 2007 and 2008, sonic telemetry was used to locate implanted sturgeon twice per week between 0900 and 1500 h. Tracking surveys were conducted outside of the study reach in the shipping channel, Lake Nicolet, Munuscong Bay and St. Josephs Channel when implanted sturgeon were not located within the study reach. In February 2009 lake sturgeon were tracked underneath the ice to determine winter locations. A directional hydrophone with a 1-km detection radius was employed to locate individual lake sturgeon. When an implanted lake sturgeon was located, GPS location, water depth and water temperature were recorded. All fish locations were entered into Arc GIS® 9.0 (ESRI, Inc) for spatial analysis. The spatial tools function within Arc GIS® 9.0 was used to calculate extent of movement and mean weekly movement rate for individual fish. Extent of movement was calculated
Lake sturgeon movement within the SMR in 2007 and 2008 was restricted to the area between the North Channel of Sugar Island to East Neebish Island (Fig. 2). However, five implanted lake sturgeon went undetected for up to 1 month during June of 2007. In 2007, implanted lake sturgeon were detected 333 times and in 2008 implanted lake sturgeon were detected 316 times. In 2007, lake sturgeon were more fully distributed throughout the study reach when compared to 2008 (Fig. 2). The mean extent of movement of lake sturgeon for implanted lake sturgeon (n = 18) in 2007 was 13.3 km (SE ± 2.7). In 2008, the mean extent of movement of lake sturgeon (n = 18) was 7.5 km (SE ± 1.6). The movement patterns and distribution of lake sturgeon varied between individuals and years (Fig. 3). Certain lake sturgeon were sedentary and rarely moved from
Table 1 Biological measurements of 18 lake sturgeon implanted with sonic transponders in the SMR, MI, 2006–2007. Capture date
Sonic tag
Floy tag
PIT tag
Total length (cm)
Girth (cm)
Total weight (kg)
Sex
5/18/2006 5/24/2006 6/7/2006 6/13/2006 6/15/2006 6/20/2006 6/23/2006 6/28/2006 6/29/2006 6/30/2006 7/12/2006 8/18/2006 6/13/2007 6/13/2007 6/20/2007 6/30/2007 7/4/2007 7/20/2007
72 khz 73 khz 70 khz 72 khz 70 khz 73 khz 71 khz 71 khz 70 khz 71 khz 72 khz 73 khz 75 khz 79 khz 77 khz 76 khz 78 khz 80 khz
10324 10321 10315 10325 T-00005 10304 10302 10311 10337 T-00018 T-00050 T-00030 010372 010367 00053 010377 010379 010391
985120031273389 985120031260569 985120031220986 985120031278417 42343D370C 985120031270653 985120031279418 985120031281139 985120031281675 4235365736 422E097759 4654366449 4235193464 985120031271505 42343F7859 4202743750 985120031284131 985120031261320
145.7 142.4 132.8 132 132.1 139.2 132.1 148.5 134.6 146.5 133.4 160.7 150 143 150.4 158 158.5 150.5
56.3 52.5 50.5 55 55.9 52.7 N/A 54.6 58.7 62.5 54.4 67 65.5 65 57.5 65 58.5 65.2
29 16.5 13.5 16.5 17.5 17 15 20 18 24.5 12.5 29 24 25 21.5 25.5 20.5 25
Unknown Unknown Male Male Unknown Male Male Unknown Male Female Unknown Female Female Female Male Female Male Female
(3-3-6-7) (5-7-7-6) (6-6-6-7) (3-5-4-7) (4-7-7-8) (4-6-5-6) (4-4-4-8) (3-6-5-6) (4-6-4-7) (3-7-4-8) (3-3-3-7) (5-5-8-8) (4-8-8) (3-3-5-4) (6-7-7) (5-5-5) (6-7-8) (3-3-5-5)
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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 lake sturgeon.
their first marked location. For instance, Fish 73: 5-7-7-6 was located near the base of Squirrel Island in the northern most portion of Lake George for the entire sampling period in 2007 and 2008. Commonly, this fish exhibited movements of less than 100 m per week. The
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 the north end of Lake George. In both years, Fish 70: 4-6-4-7 used the inflow of the North Channel of Sugar Island and Lake George
Fig. 3. Extent of movement for four sonic tagged lake sturgeon in 2007 and 2008 in the St. Marys River, MI. The number of observations for each fish ranged from 12 to 31 in 2007 and from 12 to 22 in 2008.
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extensively. Fish 71: 3-7-4-8 moved throughout the study area in 2007 while in 2008, the movements of Fish 71: 3-7-4-8 were concentrated near the confluence of the North Channel of Sugar Island and Lake George and the outflow of Lake George near East Neebish Island. The mean weekly movement rate of lake sturgeon in 2007 was 2140 m/week (SE ± 1116 m) compared to 1357 m/week (SE ± 678 m) in 2008 (Fig. 4). No significant relationship was found between mean weekly movement rate and water temperature in 2007 (R2 = 0.0862, P N 0.05) and 2008 (R2 = 0.081, P N 0.05). Reductions in movement were observed at temperatures above 15 °C in 2007 and 18 °C in 2008. In both 2007 and 2008, mean weekly movement rate of female lake sturgeon was significantly greater than mean weekly movement rate for males in 2007 and 2008 (2007: t = 2.5, df= 62, P b 0.01; 2008: t = 3.37, df= 52, P b 0.001).
Table 2 Physical habitat parameters of sites occupied by lake sturgeon in August 2007 and 2008 in SMR, MI. Current velocity (m/s)
Depth (m)
pH
DO (mg/L)
Specific conductivity (μS/m)
2007 Mean Minimum Maximum
0.23 0.04 0.43
6.11 1.43 16.15
7.75 7.41 7.98
8.72 8.02 9.25
NA NA NA
2008 Mean Minimum Maximum
0.35 0.11 0.58
6.21 2.10 14.42
8.18 7.96 8.40
8.44 7.83 8.75
105.13 95.20 107.20
burrowing mayflies (Ephemeridae), dragonfly nymphs (Gomphidae and Macromiidae), small bivalves and crayfish (Orconectes sp.). Habitat Discussion Water chemistry parameters varied little among sites where lake sturgeon were located (Table 2). In 2007 (n = 36), mean pH was 7.75 and mean dissolved oxygen was 8.02 mg/L. In 2008 (n = 20), mean pH was 8.18, mean dissolved oxygen was 8.44 mg/L, and mean. Specific conductivity was 105.13 μS/m. Lake sturgeon in 2007 (n = 69) and 2008 (n = 54) were found at a mean depth of approximately 6 m with a range from 1.43 m to 16.15 m (Table 2). In 2007 (n = 36), the current velocity at lake sturgeon locations varied between 0.04 m/s to 0.43 m/s, whereas in 2008 (n = 32) current velocity ranged from 0.11 m/s to 0.58 m/s. Lake sturgeon were found over six different substrate types in 2007 (n = 34) (Fig. 5). Silt and sand were the predominant substrate types and accounted for 47% and 21% of the observations, respectively. Gravel and clay substrate types each accounted for 12% of the total substrate observations. Lake sturgeon were infrequently observed over cobble and sand with aquatic macrophytes. In 2008 (n = 30), lake sturgeon occupied similar substrates as in 2007 except that they were not located over sand with macrophytes (Fig. 5). A quantitative assessment of benthic invertebrates was not conducted, however, ponar samples at locations occupied by sturgeon contained blood worms (Chironomidae),
Movement The lake sturgeon population monitored in the St. Marys River inhabited approximately one-third of the 112-km long river channel, which suggests that the SMR likely holds a resident population of lake sturgeon. The implanted lake sturgeon were primarily found within a 40-km reach from the North Channel of Sugar Island to the bottom of East Neebish Island. Within the study reach, lake sturgeon used core areas at the inflow of the North Channel of Sugar Island and Lake George and the outflow of Lake George near East Neebish Island. Similarly, catch data provided by Bauman et al. (2011) found that lake sturgeon in the SMR were only captured between the North Channel of Sugar Island to the southern end of Lake George. While our telemetry study demonstrated residency of lake sturgeon during spring and summer in the SMR, we were unable to conduct winter tracking surveys to verify year round residency of implanted sturgeon. However, in February of 2009, 10 of 18 tagged lake sturgeon were located through the ice at the inflow of the North Channel of Sugar Island and Lake George, further suggesting resident status. Furthermore, preliminary genetic analysis
Fig. 4. Mean weekly movement rate of lake sturgeon and mean weekly water temperature in the St. Marys River, MI in 2007 and 2008. In 2007, weekly movement calculated from 5/ 2/2007 to 8/27/2007. In 2008, weekly movement calculated from 5/27/2008 to 8/19/2008.
B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60
Fig. 5. Percent occurrence of substrate types at sites of sonic tagged lake sturgeon in the SMR, MI, August 2007 (n = 34) and 2008 (n = 30).
suggests that lake sturgeon in the SMR are distinct from other remnant populations in Lake Superior and Lake Huron (B. Evans, LSSU, unpublished data). The lack of movement of lake sturgeon in the SMR may affect metapopulation dynamics by limiting the amount of genetic exchange between the SMR population and other Great Lakes sturgeon populations. In the future more research on the seasonality of movements and degree of genetic relatedness will provide much needed information on how movement and isolation influence lake sturgeon metapopulation dynamics in the SMR and the Great Lakes. Similar to lake sturgeon in the SMR, Borkholder et al. (2002) found that a population of lake sturgeon in the Kettle River, MN, used only a 25-km reach in an unconfined river. Borkholder et al. (2002) hypothesized that the sedentary nature of the population may have been a learned behavior in response to a hydroelectric dam that had been present until 1995. Within the SMR, lake sturgeon may be constrained to the study reach by shipping activities in the shipping channel and a barrier in the form of the SMR Rapids compensating works and the Soo Locks. No tagged lake sturgeon during this study were located in proximity to the main shipping channel, and previous setline attempts in the shipping channel were unsuccessful (Bauman et al., 2011). Shipping can impact fish by increasing shear stress, altering water levels, increasing water velocity and increasing turbidity which subsequently alters fish feeding and swimming behavior (Wolter and Arlinghaus, 2003). Indirectly, dredging of shipping channels removes depositional substrates that are important for the production of benthic organisms (Allen and Hardy, 1980) that lake sturgeon feed upon. More study is warranted to determine the extent to which shipping may alter the abundance, survival and behavior of lake sturgeon in Great Lakes connecting waterways and other large river systems. While lake sturgeon in the SMR utilized a consistent area from the North Channel of Sugar Island to East Neebish Island, individual movements varied from less than 100 m to over 25 km during a seven day period. In 2008 lake sturgeon in the SMR moved on average 700 m less per week than in 2007. Additionally, the largest variation in movement between years was seen in June when water temperatures in the SMR were suitable for spawning. Variation in lake sturgeon movement rates can vary annually as a function of spawning periodicity and pre-spawning behavior (Auer, 1999). Generally, non-spawning fish inhabit relatively small areas whereas postspawning fish have been noted to undergo extensive migrations (Fortin et al., 1993; Auer, 1999). This may partially explain why mean weekly movement rate declined from 2007 to 2008. However, extensive migrations greater than 100 km which are characteristic of 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 patterns can be influenced by water temperature (Hay-Chmielewski, 1987;
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Rusak and Mosindy, 1997; McKinley et al., 1998). Within the SMR no significant relationship between movement rate and water temperature existed. However, in 2007 lake sturgeon movement rate increased as water temperatures increased. This movement may reflect the onset of the spawning migration. Similarly, in the spring in Black Lake, MI, lake sturgeon movement increased as ambient water temperatures increased (Hay-Chmielewski, 1987). Lake sturgeon movement in the SMR was reduced at temperatures exceeding 15 °C in 2007 and 18 °C in 2008. Decreased movement in lake sturgeon at increased temperatures may be due to physiological stress. McKinley et al. (1998) reported that the locomotor activity of lake sturgeon was reduced and hemorrhaging around the eyes and fins occurred as water temperature reached 19 °C. Hemorrhaging was not noted in the SMR. However, decreased activity and an increase in the prevalence of the ectoparasite Argulus sp. were seen at temperatures above 20 °C in mid-August of 2007 (A. Moerke, Lake Superior State University, unpublished data). Within the SMR, movement of implanted female lake sturgeon was significantly greater than that of male implanted lake sturgeon. In contrast, Auer (1999) found that there were no notable differences in male versus female lake sturgeon movement in the Sturgeon River, Michigan. Lake sturgeon tagged in the SMR varied in life stage attributes including age, reproductive state and sex, which results in variability in spawning periodicity and sexual maturity (Lyons and Kempinger, 1992; Auer, 1999). In Auer (1999) all lake sturgeon were mature, post spawning fish. Therefore, much of the variation caused by differences in life stage attributes was reduced. This may explain in part the variation in movement between sexes within the SMR.
Habitat Patterns of lake sturgeon distribution can be influenced by physical habitat. In shallow, homogenous systems such as Lake Winnebago and Indian Lake where the mean depth does not exceed 6 m, lake sturgeon have shown no depth preference (Priegal and Wirth, 1971; Bassett, 1982). However, with increased habitat heterogeneity (i.e. variation in depth), lake sturgeon have been shown to select depths of 6 to 11 m (Hay-Chmielewski, 1987). Similarly, in the SMR, lake sturgeon were found most commonly at depths around 6 m, although habitat selection of lake sturgeon was not measured due to sampling constraints. The SMR offers a diversity of habitats that vary in depth (1 m–25 m), substrate (silt, sand, clay, gravel, cobble, boulder) and water velocity, which may lead to lake sturgeon showing preference for certain areas. Further study is needed to quantify the level of habitat availability and selection by lake sturgeon in the SMR. Water velocity may in part determine which habitats lake sturgeon use (Engel, 1990; Knights et al., 2002). All sites used extensively by lake sturgeon in the SMR were in flowing water. Similarly, lake sturgeon in the Upper Mississippi River used transition areas (i.e. near impoundments or channel confluences) with moderate flow regimes (Knights et al., 2002). Engel (1990) found that lake sturgeon in the St. Croix River used the confluence of a river and riverine lake extensively. This is very similar to the SMR in which the highest densities of lake sturgeon telemetry observations were found near the inflow of the North Channel-Lake George. Depositional habitats, such as pools, backwaters and confluences, may provide suitable feeding areas for lake sturgeon (Knights et al., 2002; Thomas and Hass, 2002). Rusak and Mosindy (1997) in the Rainy River speculated that food availability is more important in determining lake sturgeon distribution than microhabitat variables. This indeed may be true, yet, certain microhabitat variables, such as depth, flow and substrate may facilitate increased secondary production and subsequently an increased forage base for lake sturgeon.
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Spawning site To date, telemetry data have not identified the spawning site(s) of lake sturgeon in the SMR. In 2007, five implanted lake sturgeon were not detected for up to 1 month during June. Furthermore, these “lost” sturgeon were not detected during telemetry surveys conducted outside of the study reach in the shipping channel, Munuscong Bay, and St. Josephs Channel. These individuals may have moved outside the study reach to spawn or moved into the Garden River, within the study reach, to spawn. Once relocated, all of the “lost” lake sturgeon remained within the study reach. Anecdotal evidence suggests that the Garden River and East Neebish Island rapids may be active spawning sites. The Garden River First Nation (GRFN, hereafter) has reported lake sturgeon sightings in the Garden River annually during late spring. Furthermore, the GRFN harvests lake sturgeon during the late spring within the Garden River. Additionally, local fishermen have seen lake sturgeon rolling and exhibiting spawning behavior around the East Neebish Island rapids. Both the Garden River and East Neebish Island rapids possess substrate which would 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 jump completely out of the water at the north end of Lake George and near East Neebish Island. In the Lake Winnebago system, lake sturgeon exhibit this jumping behavior approximately 14 days prior to the onset of spawning when water temperatures range from 6 to 16 °C (Bruch and Binkowski, 2002). While these reports provide valuable insight, empirical evidence of spawning must be obtained. In June of 2007, two females with partially mature gonads (eggs) were surgically implanted with sonic transponders. Hopefully, the movements of these fish will lead to the identification of the spawning location of lake sturgeon in the SMR in the near future. Conclusions Our study combined with Bauman et al. (2011) demonstrates that the SMR contains a resident lake sturgeon population that uses a small spatial area. Due to the relatively small population size (~500; Bauman et al., 2011) and lack of confirmed spawning site, lake sturgeon within the SMR are especially vulnerable to harvest, habitat degradation and catastrophic events. In the future, research must identify the spawning location to understand recruitment dynamics of SMR lake sturgeon, document the presence of juvenile lake sturgeon in an effort to protect this vulnerable life stage, and examine in greater detail the level of genetic differentiation between SMR lake sturgeon and other Great Lakes populations. Acknowledgments We are grateful to the Lake Superior State University Aquatic Research Lab summer staff (Scott Collins, Jesse Comben, Joe Menghini, Dan Operhall, Ben Turshack, and Frank Zomer) for their valuable assistance conducting all field work and processing habitat samples, the Bay Mills Indian Community for setline bait and the National Fish and Wildlife Foundation for funding. Additional thanks goes to two anonymous reviewers for comments and constructive critiques.
References Allen, K.O., Hardy, J.W., 1980. Impacts of Navigational Dredging on Fish and Wildlife: A Literature Review. Prepared by Biological Services Program, United States Fish and Wildlife Service. FWS/OBS-80/07. 80 pp. Auer, N.A., 1996. Importance of habitat and migration to sturgeons with emphasis in lake sturgeon. Can. J. Fish. Aquat. Sci. 53, 152–160. Auer, N.A., 1999. Population characteristics and movement of lake sturgeon in the Sturgeon River and Lake Superior. J. Great Lakes Res. 25, 282–293. Bassett, C., 1982. Management plan for lake sturgeon (Acipenser fulvescens) in the Indian River and Indian Lake, Alger and Schoolcraft counties, Michigan. United States Forest Service, Manistique Ranger District, Hiawatha National Forest in cooperation with Michigan Department of Natural Resources, Manistique, Michigan. Bauman, J.M., Moerke, A., Greil, R., Gerig, B., Baker, E., Chiotti, J., 2011. Population status and demographics of lake sturgeon (Acipenser fulvescens) in the St. Marys River, from 2000 to 2007. J. Great Lakes Res. 37 (Supplement 2), 47–53. Beamesderfer, R.C.P., Farr, R.A., 1997. Alternatives for the protection and restoration of sturgeons and their habitat. Environ. Biol. Fish. 48, 407–417. Boase, J., Manny, B., Kennedy, G., Thomas, M., 2004. Final report for lake sturgeon spawning in Lake Huron. National Fish and Wildlife Project no. 2003-0220-000. Borkholder, B.D., Morse, S.T., Weaver, H.T., Hugill, R.A., Linder, A.T., Schwarzkopf, L.M., Perrault, T.E., Zacher, M.J., Frank, J.A., 2002. Evidence of a year-round population of lake sturgeon in the Kettle River, Minnesota, based on radiotelemetry and tagging. N. Am. J. Fish. Manage. 22, 888–894. Bray, K.E., 1996. Habitat models as tools for evaluating historic change in the St. Marys River. Can. J. Fish. Aquat. Sci. 53, 88–98. Bruch, R.M., Binkowski, F.P., 2002. Spawning behavior of lake sturgeon (Acipenser fulvescens). J. Appl. Ichthyol. 18, 570–579. 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. Fielder, D.G., Waybrant, J.R., 1998. Fish population surveys of the St. Marys River, 1975– 1995, and recommendations for management. Michigan Department of Natural Resources Fisheries Division Research Report. No. 2048. Fortin, R., Mongeau, J.R., Desjardins, G., Dumont, P., 1993. Movements and biological statistics of lake sturgeon (Acipenser fulvescens) populations from the St. Lawrence and Ottawa River system, Quebec. Can. J. Zool. 71, 638–650. Harkness, W.J.K., Dymond, J.R., 1961. The lake sturgeon. Ontario Department of Lands and Forests, Toronto, Ontario. Hay-Chmielewski, E.M., 1987. Habitat preferences and movement of the lake sturgeon (Acipenser fulvescens) in Black Lake Michigan. Michigan Department of Natural Resources, Fisheries Research Report 1949, Ann Arbor, Michigan. Hay-Chmielewski, E.M., Whelan, G., 1997. Lake Sturgeon Rehabilitation Strategy. Michigan Department of Natural Resources, Fisheries Division Special Report 18. Knights, B.C., Vallazza, J., Zigler, S., Dewey, M., 2002. Habitat and movement of lake sturgeon in the Upper Mississippi River System, USA. Trans. Am. Fish. Soc. 131, 507–522. LaHaye, M., Branchaud, A., Gendron, M., Verdon, R., Fortin, R., 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. Can. J. Zool. 70, 1681–1689. Lallaman, J.J., Damstra, R.A., Galarowicz, T.L., 2008. Population assessment and movement of lake sturgeon (Acipenser fulvescens) in the Manistee River, Michigan, USA. J. Appl. Ichthyol. 24, 1–6. Lyons, J., Kempinger, J.J., 1992. Movements of adult lake sturgeon in the Lake Winnebago system. Wisconsin Department of Natural Resources, Research Report 156, Madison, Wisconsin. McKinley, R.S., Van Der Kraak, G., Powers, G., 1998. Seasonal migrations and reproductive patters in the lake sturgeon, Acipenser fulvescens, in the vicinity of hydroelectric stations in northern Ontario. Environ. Biol. Fish. 51, 245–256. Priegal, G.R., Wirth, T.L., 1971. The lake sturgeon: its life history, ecology and management. Wisconsin Department of Natural Resources, Madison, Wisconsin. Rusak, J.A., Mosindy, T., 1997. Seasonal Movements of lake sturgeon in Lake of the Woods and Rainy River, Ontario. Can. J. Zool. 74, 383–395. Scott, W.B., Crossman, E.J., 1973. Freshwater fishes of Canada. Fisheries Research Board of Canada, Bulletin 184, Ottawa, Ontario. Thomas, M.V., Hass, R.C., 1999. Capture of lake sturgeon with setlines in the St. Clair River, Michigan. N. Am. J. Fish. Manage. 19, 610–612. Thomas, M.V., Hass, R.C., 2002. Abundance, age structure, and spatial distribution of lake sturgeon, Acipenser fulvescens, in the St. Clair System. J. Appl. Ichthyol. 18, 495–501. Wolter, C., Arlinghaus, R., 2003. Navigation impacts of freshwater fish assemblages: the ecological relevance of swimming performance. Rev. Fish Biol. Fish. 13, 63–89.
Contents lists available at ScienceDirect
Journal of Great Lakes Research j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / j g l r
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 b
Aquatic Research Laboratory, Lake Superior State University, 650 W. Easterday Ave, Sault Ste. Marie, MI 49783, USA United States Fish and Wildlife Service, Alpena National Fish and Wildlife Conservation Office, 145 Water Street, Federal Building Rm. 204, Alpena, MI 49707, USA
a r t i c l e
i n f o
Article history: Received 30 June 2009 Accepted 11 February 2010 Available online 20 October 2010 Communicated by R. Marshall Werner Index words: Lake sturgeon St. Marys River Telemetry Acipenser fulvescens
a b s t r a c t Historically, the St. Marys River (SMR), Michigan, provided suitable habitat for lake sturgeon (Acipenser fulvescens) but their population declined dramatically during the past century due to overharvest and habitat alteration. Since 2000, the Lake Superior State University Aquatic Research Lab has monitored a remnant population of lake sturgeon in the SMR. During 2007 and 2008, lake sturgeon were implanted with sonic transponders to determine spatial extent, movement patterns, and habitat use in the SMR. Telemetry observations indicated that lake sturgeon inhabit a 40 km river reach, representing approximately one-third of the total area of the SMR. Lake sturgeon movement in the SMR was confined to an area between the North Channel of Sugar Island to the southern end of East Neebish Island, with the majority centered around the north end of Lake George. Additionally, lake sturgeon were not observed in the main shipping channel which suggests that they may actively avoid areas with high shipping traffic. During this study, individual weekly movement rates of lake sturgeon varied from under 100 m to over 25 km. Lake sturgeon used transition areas between lotic and lentic waters extensively. These areas create depositional habitats that may be essential foraging areas for lake sturgeon in the SMR. Telemetry results to date have not confirmed the spawning location of lake sturgeon within the SMR. However, two females with partially mature eggs were tagged in 2007 and may spawn within the next 2 years. Their movements could lead to the positive identification of the spawning 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 lived potamodromous fish endemic to the Great Lakes basin (Harkness and Dymond, 1961; Scott and Crossman, 1973). Regular migrations associated with spawning and smaller movements associated with feeding have been observed in lake sturgeon, as well as other sturgeon species worldwide (Beamesderfer and Farr, 1997). Typically, lake sturgeon undergo migrations from lakes or large rivers to smaller tributaries to spawn in the spring (Fortin et al., 1993; Auer, 1999; Knights et al., 2002; Lallaman et al., 2008). After spawning, lake sturgeon migrate out of these tributary rivers and return to their respective lakes and rivers (Auer, 1996). Studies in Lake of the WoodsRainy Lake, Lake Winnebago, and the St. Lawrence Seaway have documented extensive migrations in lake sturgeon (Fortin et al., 1993; Rusak and Mosindy, 1997). Auer (1999) found that lake sturgeon from the Sturgeon River, Michigan, were capable of post-spawning move-
⁎ Corresponding author. E-mail addresses: bsgerig@ufl.edu (B. Gerig), [email protected] (A. Moerke), [email protected] (R. Greil), [email protected] (S. Koproski). 1 Current address: Department of Wildlife Ecology and Conservation, University of Florida, 110 Newins-Ziegler Hall, PO Box 110430, Gainesville, FL 32611-0430, USA.
ments exceeding 330 km. In contrast, others have indicated that lake sturgeon may remain in their spawning river for much or all of the year (Lyons and Kempinger, 1992; Rusak and Mosindy, 1997). Patterns of movement not associated with spawning migrations are poorly documented, and it remains unclear if lake sturgeon have distinct home ranges. Within Wisconsin, a mark-recapture study revealed that lake sturgeon in Lake Winnebago migrated extensively to 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 with distinct areas used for resting, foraging and over-wintering. In contrast, lake sturgeon within Black Lake were found to move randomly and have no defined home range (Hay-Chmielewski, 1987). Due to differences in life stage and variation in the physical habitats that are used for spawning, resting, foraging and overwintering, generalities are difficult to make when characterizing lake sturgeon movement patterns (Boase et al., 2004). The Michigan Department of Natural Resources (MI DNR) in the Lake Sturgeon Rehabilitation Strategy lists the identification of current population status as essential to the recovery of lake sturgeon (Hay-Chmielewski and Whelan, 1997). Specifically, fisheries managers must determine patterns of movement, stock origin (i.e. resident or non-resident) and spawning locations to properly assess
0380-1330/$ – see front matter © 2010 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jglr.2010.09.007
B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60
and manage remnant lake sturgeon populations. Currently, the status of lake sturgeon within Great Lakes connecting waterways is poorly understood due in part to the low abundance of lake sturgeon and the logistical challenges (i.e. depth and turbidity) of sampling such systems. In contrast to rivers that allow for the visual observation of sturgeon, Great Lakes connecting waterways necessitate the use of mark-recapture techniques and telemetry to determine lake sturgeon abundance, distribution and habitat use (Boase et al., 2004). For instance, the St. Marys River (SMR, hereafter) located in the Eastern Upper Peninsula of Michigan, historically held a population of lake sturgeon. Extensive surveys conducted by the MI DNR from 1975 to 1995 found that lake sturgeon abundance was declining and by 1995 lake sturgeon were absent from the survey (Fielder and Waybrant, 1998). Yet since 2000, the Lake Superior State University Aquatic Research Lab has captured over 230 sturgeon in the SMR, with a recapture rate of approximately 15% during summer assessments (Bauman et al., 2011). Despite the SMR being identified in the MI DNR Lake Sturgeon Rehabilitation Strategy as having high suitability for lake sturgeon, little data currently exist on this population. Specifically, knowledge gaps that persist in the SMR include an understanding of the spatial distribution, movement patterns, spawning location (s) and habitat use. The goals of this study were to: (1) determine the
55
spatial extent of lake sturgeon within the SMR, (2) document interannual spring and summer movement patterns of lake sturgeon, and (3) document habitat characteristics of locations where lake sturgeon were located within the SMR. Methods Study site The SMR is the sole connecting waterway between Lake Superior and Lake Huron and the largest tributary of Lake Huron (Fig. 1). Water leaves Whitefish Bay in Lake Superior and travels 112 river kilometers to the Detour Passage in Lake Huron. The SMR is divided into the upper and lower river at river kilometer 22.5 by the SMR Rapids. The Soo Locks, Edison Sault hydroelectric canal, and the SMR Rapids compensating works form a barrier that likely limits the movement of lake sturgeon between the upper and lower river. The main river channel has been altered extensively to a depth greater than 8 m to allow the passage of commercial freighters between Lake Superior and Lake Huron. Additionally, the SMR compensating works alter the natural flow regime and restrict discharge to less than 50% of the historic outflow (Bray, 1996). Despite the significant anthropogenic
Fig. 1. The 40-km study reach from the North Channel of Sugar Island to Munuscong Bay in the St. Marys River. Dotted lines represent the shipping channel. Map inset illustrates location of the St. Marys River in reference to the upper Great Lakes.
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B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60
alterations in the SMR, the area from the North Channel of Sugar Island to East Neebish Island continues to support a population of lake sturgeon. Within this reach lake sturgeon have access to tributary rivers and mainstem areas that would provide suitable spawning habitat. The study reach, from the North Channel of Sugar Island to East Neebish Island, was ultimately defined by the area that implanted lake 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 by Thomas and Hass (1999). Twelve lake sturgeon were implanted with sonic transponders (Sonotronics Inc.) in 2006 and six additional sturgeon were implanted in 2007. Lake sturgeon that were implanted ranged between 132 and 160 cm in total length and 12.5 to 29 kg in total weight (Table 1). The sex of the implanted lake sturgeon was determined by the visual observation of ovaries or testes during the surgical implantation of sonic transponders. Of the 18 sonic tagged lake sturgeon, 6 were female, 7 were male and 5 did not exhibit mature gonads and were unable to be sexed with confidence. The sonic transponder was inserted by making a 6- to 8-cm incision into the ventral surface of the fish near the midline posterior to the pelvic girdle. The tag was placed within the body cavity and the incision was sutured closed with 10–12 individual stitches. Cyanoacrylate was applied along the incision and each individual suture to ensure closure. Each sonic transponder has a 4-year battery life to enable long-term tracking of the implanted lake sturgeon.
as a surrogate of home range because of the lack of winter telemetry observations. The extent of movement was measured as the distance between the most upstream location and the furthest downstream location of each implanted lake sturgeon. Weekly movement rate was calculated as the linear distance traveled from the beginning to end of a 7 day period in both 2007 and 2008. Extent of movement and weekly movement rate were measured as the shortest linear distance between locations which may underestimate the actual distance traveled. Linear regression was used to compare mean weekly movement rate to water temperatures within the river in 2007 and 2008. Male mean weekly movement rate was compared to female mean weekly movement rate using a two tailed t-test. Lake sturgeon that were not sexed were not included in this analysis. Habitat Habitat attributes were measured at sites where lake sturgeon were located during tracking surveys in August 2007 and 2008. At each sample site, a Hydrolab® Quanta or MiniSonde was used to measure pH, dissolved oxygen (mg/L) and Specific conductivity (μS/ m) approximately 1 m above the river bottom. Water velocity was measured to the nearest 0.01 m/s using a Rickly® hydrologic flow meter approximately 1 m above the river bottom. Substrate type was determined using a ponar sampler. Substrate was classified using a modified Wentworth Scale into six categories based on visual observation of silt, sand, clay, gravel, cobble and sand with macrophytes. Results
Tracking methods Movement During the spring and summer sampling period of 2007 and 2008, sonic telemetry was used to locate implanted sturgeon twice per week between 0900 and 1500 h. Tracking surveys were conducted outside of the study reach in the shipping channel, Lake Nicolet, Munuscong Bay and St. Josephs Channel when implanted sturgeon were not located within the study reach. In February 2009 lake sturgeon were tracked underneath the ice to determine winter locations. A directional hydrophone with a 1-km detection radius was employed to locate individual lake sturgeon. When an implanted lake sturgeon was located, GPS location, water depth and water temperature were recorded. All fish locations were entered into Arc GIS® 9.0 (ESRI, Inc) for spatial analysis. The spatial tools function within Arc GIS® 9.0 was used to calculate extent of movement and mean weekly movement rate for individual fish. Extent of movement was calculated
Lake sturgeon movement within the SMR in 2007 and 2008 was restricted to the area between the North Channel of Sugar Island to East Neebish Island (Fig. 2). However, five implanted lake sturgeon went undetected for up to 1 month during June of 2007. In 2007, implanted lake sturgeon were detected 333 times and in 2008 implanted lake sturgeon were detected 316 times. In 2007, lake sturgeon were more fully distributed throughout the study reach when compared to 2008 (Fig. 2). The mean extent of movement of lake sturgeon for implanted lake sturgeon (n = 18) in 2007 was 13.3 km (SE ± 2.7). In 2008, the mean extent of movement of lake sturgeon (n = 18) was 7.5 km (SE ± 1.6). The movement patterns and distribution of lake sturgeon varied between individuals and years (Fig. 3). Certain lake sturgeon were sedentary and rarely moved from
Table 1 Biological measurements of 18 lake sturgeon implanted with sonic transponders in the SMR, MI, 2006–2007. Capture date
Sonic tag
Floy tag
PIT tag
Total length (cm)
Girth (cm)
Total weight (kg)
Sex
5/18/2006 5/24/2006 6/7/2006 6/13/2006 6/15/2006 6/20/2006 6/23/2006 6/28/2006 6/29/2006 6/30/2006 7/12/2006 8/18/2006 6/13/2007 6/13/2007 6/20/2007 6/30/2007 7/4/2007 7/20/2007
72 khz 73 khz 70 khz 72 khz 70 khz 73 khz 71 khz 71 khz 70 khz 71 khz 72 khz 73 khz 75 khz 79 khz 77 khz 76 khz 78 khz 80 khz
10324 10321 10315 10325 T-00005 10304 10302 10311 10337 T-00018 T-00050 T-00030 010372 010367 00053 010377 010379 010391
985120031273389 985120031260569 985120031220986 985120031278417 42343D370C 985120031270653 985120031279418 985120031281139 985120031281675 4235365736 422E097759 4654366449 4235193464 985120031271505 42343F7859 4202743750 985120031284131 985120031261320
145.7 142.4 132.8 132 132.1 139.2 132.1 148.5 134.6 146.5 133.4 160.7 150 143 150.4 158 158.5 150.5
56.3 52.5 50.5 55 55.9 52.7 N/A 54.6 58.7 62.5 54.4 67 65.5 65 57.5 65 58.5 65.2
29 16.5 13.5 16.5 17.5 17 15 20 18 24.5 12.5 29 24 25 21.5 25.5 20.5 25
Unknown Unknown Male Male Unknown Male Male Unknown Male Female Unknown Female Female Female Male Female Male Female
(3-3-6-7) (5-7-7-6) (6-6-6-7) (3-5-4-7) (4-7-7-8) (4-6-5-6) (4-4-4-8) (3-6-5-6) (4-6-4-7) (3-7-4-8) (3-3-3-7) (5-5-8-8) (4-8-8) (3-3-5-4) (6-7-7) (5-5-5) (6-7-8) (3-3-5-5)
B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60
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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 lake sturgeon.
their first marked location. For instance, Fish 73: 5-7-7-6 was located near the base of Squirrel Island in the northern most portion of Lake George for the entire sampling period in 2007 and 2008. Commonly, this fish exhibited movements of less than 100 m per week. The
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 the north end of Lake George. In both years, Fish 70: 4-6-4-7 used the inflow of the North Channel of Sugar Island and Lake George
Fig. 3. Extent of movement for four sonic tagged lake sturgeon in 2007 and 2008 in the St. Marys River, MI. The number of observations for each fish ranged from 12 to 31 in 2007 and from 12 to 22 in 2008.
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extensively. Fish 71: 3-7-4-8 moved throughout the study area in 2007 while in 2008, the movements of Fish 71: 3-7-4-8 were concentrated near the confluence of the North Channel of Sugar Island and Lake George and the outflow of Lake George near East Neebish Island. The mean weekly movement rate of lake sturgeon in 2007 was 2140 m/week (SE ± 1116 m) compared to 1357 m/week (SE ± 678 m) in 2008 (Fig. 4). No significant relationship was found between mean weekly movement rate and water temperature in 2007 (R2 = 0.0862, P N 0.05) and 2008 (R2 = 0.081, P N 0.05). Reductions in movement were observed at temperatures above 15 °C in 2007 and 18 °C in 2008. In both 2007 and 2008, mean weekly movement rate of female lake sturgeon was significantly greater than mean weekly movement rate for males in 2007 and 2008 (2007: t = 2.5, df= 62, P b 0.01; 2008: t = 3.37, df= 52, P b 0.001).
Table 2 Physical habitat parameters of sites occupied by lake sturgeon in August 2007 and 2008 in SMR, MI. Current velocity (m/s)
Depth (m)
pH
DO (mg/L)
Specific conductivity (μS/m)
2007 Mean Minimum Maximum
0.23 0.04 0.43
6.11 1.43 16.15
7.75 7.41 7.98
8.72 8.02 9.25
NA NA NA
2008 Mean Minimum Maximum
0.35 0.11 0.58
6.21 2.10 14.42
8.18 7.96 8.40
8.44 7.83 8.75
105.13 95.20 107.20
burrowing mayflies (Ephemeridae), dragonfly nymphs (Gomphidae and Macromiidae), small bivalves and crayfish (Orconectes sp.). Habitat Discussion Water chemistry parameters varied little among sites where lake sturgeon were located (Table 2). In 2007 (n = 36), mean pH was 7.75 and mean dissolved oxygen was 8.02 mg/L. In 2008 (n = 20), mean pH was 8.18, mean dissolved oxygen was 8.44 mg/L, and mean. Specific conductivity was 105.13 μS/m. Lake sturgeon in 2007 (n = 69) and 2008 (n = 54) were found at a mean depth of approximately 6 m with a range from 1.43 m to 16.15 m (Table 2). In 2007 (n = 36), the current velocity at lake sturgeon locations varied between 0.04 m/s to 0.43 m/s, whereas in 2008 (n = 32) current velocity ranged from 0.11 m/s to 0.58 m/s. Lake sturgeon were found over six different substrate types in 2007 (n = 34) (Fig. 5). Silt and sand were the predominant substrate types and accounted for 47% and 21% of the observations, respectively. Gravel and clay substrate types each accounted for 12% of the total substrate observations. Lake sturgeon were infrequently observed over cobble and sand with aquatic macrophytes. In 2008 (n = 30), lake sturgeon occupied similar substrates as in 2007 except that they were not located over sand with macrophytes (Fig. 5). A quantitative assessment of benthic invertebrates was not conducted, however, ponar samples at locations occupied by sturgeon contained blood worms (Chironomidae),
Movement The lake sturgeon population monitored in the St. Marys River inhabited approximately one-third of the 112-km long river channel, which suggests that the SMR likely holds a resident population of lake sturgeon. The implanted lake sturgeon were primarily found within a 40-km reach from the North Channel of Sugar Island to the bottom of East Neebish Island. Within the study reach, lake sturgeon used core areas at the inflow of the North Channel of Sugar Island and Lake George and the outflow of Lake George near East Neebish Island. Similarly, catch data provided by Bauman et al. (2011) found that lake sturgeon in the SMR were only captured between the North Channel of Sugar Island to the southern end of Lake George. While our telemetry study demonstrated residency of lake sturgeon during spring and summer in the SMR, we were unable to conduct winter tracking surveys to verify year round residency of implanted sturgeon. However, in February of 2009, 10 of 18 tagged lake sturgeon were located through the ice at the inflow of the North Channel of Sugar Island and Lake George, further suggesting resident status. Furthermore, preliminary genetic analysis
Fig. 4. Mean weekly movement rate of lake sturgeon and mean weekly water temperature in the St. Marys River, MI in 2007 and 2008. In 2007, weekly movement calculated from 5/ 2/2007 to 8/27/2007. In 2008, weekly movement calculated from 5/27/2008 to 8/19/2008.
B. Gerig et al. / Journal of Great Lakes Research 37 (2011) 54–60
Fig. 5. Percent occurrence of substrate types at sites of sonic tagged lake sturgeon in the SMR, MI, August 2007 (n = 34) and 2008 (n = 30).
suggests that lake sturgeon in the SMR are distinct from other remnant populations in Lake Superior and Lake Huron (B. Evans, LSSU, unpublished data). The lack of movement of lake sturgeon in the SMR may affect metapopulation dynamics by limiting the amount of genetic exchange between the SMR population and other Great Lakes sturgeon populations. In the future more research on the seasonality of movements and degree of genetic relatedness will provide much needed information on how movement and isolation influence lake sturgeon metapopulation dynamics in the SMR and the Great Lakes. Similar to lake sturgeon in the SMR, Borkholder et al. (2002) found that a population of lake sturgeon in the Kettle River, MN, used only a 25-km reach in an unconfined river. Borkholder et al. (2002) hypothesized that the sedentary nature of the population may have been a learned behavior in response to a hydroelectric dam that had been present until 1995. Within the SMR, lake sturgeon may be constrained to the study reach by shipping activities in the shipping channel and a barrier in the form of the SMR Rapids compensating works and the Soo Locks. No tagged lake sturgeon during this study were located in proximity to the main shipping channel, and previous setline attempts in the shipping channel were unsuccessful (Bauman et al., 2011). Shipping can impact fish by increasing shear stress, altering water levels, increasing water velocity and increasing turbidity which subsequently alters fish feeding and swimming behavior (Wolter and Arlinghaus, 2003). Indirectly, dredging of shipping channels removes depositional substrates that are important for the production of benthic organisms (Allen and Hardy, 1980) that lake sturgeon feed upon. More study is warranted to determine the extent to which shipping may alter the abundance, survival and behavior of lake sturgeon in Great Lakes connecting waterways and other large river systems. While lake sturgeon in the SMR utilized a consistent area from the North Channel of Sugar Island to East Neebish Island, individual movements varied from less than 100 m to over 25 km during a seven day period. In 2008 lake sturgeon in the SMR moved on average 700 m less per week than in 2007. Additionally, the largest variation in movement between years was seen in June when water temperatures in the SMR were suitable for spawning. Variation in lake sturgeon movement rates can vary annually as a function of spawning periodicity and pre-spawning behavior (Auer, 1999). Generally, non-spawning fish inhabit relatively small areas whereas postspawning fish have been noted to undergo extensive migrations (Fortin et al., 1993; Auer, 1999). This may partially explain why mean weekly movement rate declined from 2007 to 2008. However, extensive migrations greater than 100 km which are characteristic of 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 patterns can be influenced by water temperature (Hay-Chmielewski, 1987;
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Rusak and Mosindy, 1997; McKinley et al., 1998). Within the SMR no significant relationship between movement rate and water temperature existed. However, in 2007 lake sturgeon movement rate increased as water temperatures increased. This movement may reflect the onset of the spawning migration. Similarly, in the spring in Black Lake, MI, lake sturgeon movement increased as ambient water temperatures increased (Hay-Chmielewski, 1987). Lake sturgeon movement in the SMR was reduced at temperatures exceeding 15 °C in 2007 and 18 °C in 2008. Decreased movement in lake sturgeon at increased temperatures may be due to physiological stress. McKinley et al. (1998) reported that the locomotor activity of lake sturgeon was reduced and hemorrhaging around the eyes and fins occurred as water temperature reached 19 °C. Hemorrhaging was not noted in the SMR. However, decreased activity and an increase in the prevalence of the ectoparasite Argulus sp. were seen at temperatures above 20 °C in mid-August of 2007 (A. Moerke, Lake Superior State University, unpublished data). Within the SMR, movement of implanted female lake sturgeon was significantly greater than that of male implanted lake sturgeon. In contrast, Auer (1999) found that there were no notable differences in male versus female lake sturgeon movement in the Sturgeon River, Michigan. Lake sturgeon tagged in the SMR varied in life stage attributes including age, reproductive state and sex, which results in variability in spawning periodicity and sexual maturity (Lyons and Kempinger, 1992; Auer, 1999). In Auer (1999) all lake sturgeon were mature, post spawning fish. Therefore, much of the variation caused by differences in life stage attributes was reduced. This may explain in part the variation in movement between sexes within the SMR.
Habitat Patterns of lake sturgeon distribution can be influenced by physical habitat. In shallow, homogenous systems such as Lake Winnebago and Indian Lake where the mean depth does not exceed 6 m, lake sturgeon have shown no depth preference (Priegal and Wirth, 1971; Bassett, 1982). However, with increased habitat heterogeneity (i.e. variation in depth), lake sturgeon have been shown to select depths of 6 to 11 m (Hay-Chmielewski, 1987). Similarly, in the SMR, lake sturgeon were found most commonly at depths around 6 m, although habitat selection of lake sturgeon was not measured due to sampling constraints. The SMR offers a diversity of habitats that vary in depth (1 m–25 m), substrate (silt, sand, clay, gravel, cobble, boulder) and water velocity, which may lead to lake sturgeon showing preference for certain areas. Further study is needed to quantify the level of habitat availability and selection by lake sturgeon in the SMR. Water velocity may in part determine which habitats lake sturgeon use (Engel, 1990; Knights et al., 2002). All sites used extensively by lake sturgeon in the SMR were in flowing water. Similarly, lake sturgeon in the Upper Mississippi River used transition areas (i.e. near impoundments or channel confluences) with moderate flow regimes (Knights et al., 2002). Engel (1990) found that lake sturgeon in the St. Croix River used the confluence of a river and riverine lake extensively. This is very similar to the SMR in which the highest densities of lake sturgeon telemetry observations were found near the inflow of the North Channel-Lake George. Depositional habitats, such as pools, backwaters and confluences, may provide suitable feeding areas for lake sturgeon (Knights et al., 2002; Thomas and Hass, 2002). Rusak and Mosindy (1997) in the Rainy River speculated that food availability is more important in determining lake sturgeon distribution than microhabitat variables. This indeed may be true, yet, certain microhabitat variables, such as depth, flow and substrate may facilitate increased secondary production and subsequently an increased forage base for lake sturgeon.
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Spawning site To date, telemetry data have not identified the spawning site(s) of lake sturgeon in the SMR. In 2007, five implanted lake sturgeon were not detected for up to 1 month during June. Furthermore, these “lost” sturgeon were not detected during telemetry surveys conducted outside of the study reach in the shipping channel, Munuscong Bay, and St. Josephs Channel. These individuals may have moved outside the study reach to spawn or moved into the Garden River, within the study reach, to spawn. Once relocated, all of the “lost” lake sturgeon remained within the study reach. Anecdotal evidence suggests that the Garden River and East Neebish Island rapids may be active spawning sites. The Garden River First Nation (GRFN, hereafter) has reported lake sturgeon sightings in the Garden River annually during late spring. Furthermore, the GRFN harvests lake sturgeon during the late spring within the Garden River. Additionally, local fishermen have seen lake sturgeon rolling and exhibiting spawning behavior around the East Neebish Island rapids. Both the Garden River and East Neebish Island rapids possess substrate which would 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 jump completely out of the water at the north end of Lake George and near East Neebish Island. In the Lake Winnebago system, lake sturgeon exhibit this jumping behavior approximately 14 days prior to the onset of spawning when water temperatures range from 6 to 16 °C (Bruch and Binkowski, 2002). While these reports provide valuable insight, empirical evidence of spawning must be obtained. In June of 2007, two females with partially mature gonads (eggs) were surgically implanted with sonic transponders. Hopefully, the movements of these fish will lead to the identification of the spawning location of lake sturgeon in the SMR in the near future. Conclusions Our study combined with Bauman et al. (2011) demonstrates that the SMR contains a resident lake sturgeon population that uses a small spatial area. Due to the relatively small population size (~500; Bauman et al., 2011) and lack of confirmed spawning site, lake sturgeon within the SMR are especially vulnerable to harvest, habitat degradation and catastrophic events. In the future, research must identify the spawning location to understand recruitment dynamics of SMR lake sturgeon, document the presence of juvenile lake sturgeon in an effort to protect this vulnerable life stage, and examine in greater detail the level of genetic differentiation between SMR lake sturgeon and other Great Lakes populations. Acknowledgments We are grateful to the Lake Superior State University Aquatic Research Lab summer staff (Scott Collins, Jesse Comben, Joe Menghini, Dan Operhall, Ben Turshack, and Frank Zomer) for their valuable assistance conducting all field work and processing habitat samples, the Bay Mills Indian Community for setline bait and the National Fish and Wildlife Foundation for funding. Additional thanks goes to two anonymous reviewers for comments and constructive critiques.
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