Population Characteristics and Movements of Lake Sturgeon in the Sturgeon River and Lake Superior

J. Great Lakes Res. 25(2):282–293 Internat. Assoc. Great Lakes Res., 1999

Population Characteristics and Movements of Lake Sturgeon in the Sturgeon River and Lake Superior Nancy A. Auer* Department of Biological Sciences Michigan Technological University 1400 Townsend Drive Houghton, Michigan 49931 ABSTRACT. A 2.6-km reach of the Sturgeon River, containing two sets of rapids, is an important spawning site to a native population of lake sturgeon, Acipenser fulvescens, which ranges widely into southern Lake Superior. Similar spawning areas in other Great Lake tributaries may also be important to the protection and rehabilitation of lake sturgeon throughout this region. Information on range and habitat needs of this species, which is considered “threatened” in the State of Michigan, was obtained from the Sturgeon River spawning population from 1987 to 1995. Radio-tracking was employed to determine movements and habitat use by post-spawning lake sturgeon. Telemetry data from 25 fish were supplemented with data obtained through identification tag returns. During the study 925 lake sturgeon were handled; 86 returned to spawn 1 time and 12 returned 2 times. Spawning intervals for male lake sturgeon were commonly 2, 3, or 4 years; yearly spawning by males was never observed. Females returned to spawn after 3 to 7 years. From 1991 to 1995 the male:female sex ratio at the spawning site was 1.25 to 2.7. In 1990 13 of 18 adults fitted with transmitters moved out of the river within 9 days. Upon reaching Portage Lake nine individuals spent time in shallow (maximum depth, 6 m) Pike Bay. After 3 to 53 days (mean, 22) tagged fish moved into the deeper water of Portage Lake (maximum depth, 17 m) and ranged more widely. Three fish were located in Keweenaw Bay, Lake Superior by late August. Identification tag returns reveal that lake sturgeon traveled 70 to 280 km from the spawning site throughout southern Lake Superior. INDEX WORDS:

Lake sturgeon, movements, range, spawning, Sturgeon River, Lake Superior.

INTRODUCTION Lake sturgeon, Acipenser fulvescens, were once abundant throughout the Great Lakes basin but habitat degradation caused by deforestation, log sluicing, and sawmill waste in the early 1800s combined with over-harvest in the early 1900s substantially reduced abundance of this species in the Great Lakes (Harkness and Dymond 1961). Most remaining populations of this species are restricted in movement by dams or navigation locks (Folz and Meyers 1985, Hay-Chmielewski 1987, Thuemler 1988). One persistent population spawns in the Sturgeon River, a Michigan tributary to Lake Superior (Fig.1). These large fish, which are about 140 cm total length, 18 cm high, and weigh 20 kg, spawn in rapids immediately downstream from a *Corresponding

small hydroelectric facility built in 1930. Research described here was undertaken to determine: 1) the time adult lake sturgeon arrive and remain in the river near the vicinity of the hydroelectric facility and are exposed to water level fluctuations produced by the facility operation; 2) the geographic range of post-spawning lake sturgeon; and 3) the sex ratio, incremental growth, age, tag retention, and periodicity of spawning for lake sturgeon at this site. STUDY AREA Sturgeon River The Sturgeon River flows for more than 130 km through Houghton and Baraga Counties in Michigan’s upper peninsula. A hydroelectric facility dam about 69 km above the mouth creates an impassable barrier to upstream migration of fish (Fig.1). There

author. E-mail: [email protected]

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and requested a change in operation from “peaking” to near run-of-the-river (ROR)(Auer 1996). Peaking operation occurred in 1987 and 1988; 1989 and 1990 were years of transition because of numerous shutdowns for various relicensing studies; and from 1991 through 1995 the facility operated near, but not full ROR, with little interruption. Peaking operation resulted in dramatic reductions in flow for 15 to 18 hours a day. The change to near ROR was reflected in a reduction in time lake sturgeon were observed on site, an increase in total number of individuals spawning, an increase in the number of fish greater than 22.5 kg, and an increase in the number of fish seen in a reproductively ready state (Auer 1996).

FIG. 1. Location of the Sturgeon River, Michigan, Prickett hydroelectric facility, spawning rapids, Portage Lake system, and Keweenaw Bay, Lake Superior.

is no record to determine if the dam is sited on a natural barrier to upstream migration. An impassable natural barrier (falls) exists 6 km above the dam. The river below the dam meanders through agricultural and forested land and is a warmwater stream with an average alkalinity of 1 meq/L [50 mg/L (CaCO3)] and a pH of 8 (Stone and Webster 1991). Average annual discharge below the dam for the spawning months of April and May is 33 and 22.5 m 3 /s (Blumer et al. 1993). Lake sturgeon spawn below the dam in a 2.6-km reach of river with two sets of rapids. This reach of the river has an average width of 30 to 40 m, an average depth of 25 cm, and has many large boulders and deep pools. The Federal Energy Regulatory Commission (FERC) relicensed this facility during this study

Portage Lake System, Keweenaw Bay, and Lake Superior The Sturgeon River flows into Portage Lake, Michigan. This lake is about 17 km2 in area, has a maximum depth of 16.5 m, an average depth of 8 m, and conductivity of about 100 µmho/cm (Spain et al. 1969). The bottom of Portage Lake has been altered in many areas by years of disposal of tailings from copper mines operated in the late 1800s. Pike Bay is a 1.3-km2, shallow bay (maximum depth 6 m) in Portage Lake west of the mouth of the Sturgeon River (Fig. 1). A man-made channel, the “cut,” 1.6 km above the mouth of the Sturgeon River allows small boats to enter the river from Pike Bay and avoid the shallow water in the delta at the natural mouth of the river. At its north end, Portage Lake splits into a 29-km northwest arm, which connects with Lake Superior, and an 8-km northeast arm, which connects with Torch Lake. The northwest arm was dredged open to Lake Superior in 1873 (Lawrence 1954). At the southeast end of Portage Lake a 9.5-km-long, 7.5m-deep shipping channel has been dredged through the Sturgeon River sloughs which flows into Keweenaw Bay, Lake Superior. Keweenaw Bay varies in depth from 2 m to 110 m. The lower portion of the bay has a sand substrate and a mean depth of 22.5 m. METHODS Fish Capture, Measurement, and Sex Determination Adult lake sturgeon were captured with large (81 × 51 × 76 cm) dip nets near the hydroelectric facility each spring. In 1987 and 1988 fish were

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captured during the low-flow period after daily peaking operation ended. From 1989 through 1995 capture took place during facility shut-down for other studies or at the request of the author. Surveys were started at the lower-most portion of the 2.6km area of rapids because fish drifted out of the rapids when water levels began to fall. Surveys began each spring when water temperatures approached 9°C, just prior to expected spawning runs. Total length, weight, sex, and reproductive condition were recorded for each fish. Length was measured to the nearest centimeter. Weight was measured to the nearest half kg. Sex was determined by placing pressure on the ventral surface of the fish to express gametes and by examining the vent area. Fish were recorded as females if they produced eggs or had soft, red, fleshy tissue hanging from the vent. Males produced milt and had firm, white tissue near the vent. The sex of fish not displaying these characteristics was recorded as “undetermined.” Evidence of previous tags and scars was noted and capture location within the river system was noted. Aging The ages of 12 fish were determined from cross sections of pectoral fin rays taken from live fish in 1987 and 1990. Sections were removed with a hacksaw, dried, and then thinly sliced with a jewelers saw. Annular rings were counted by three independent, experienced individuals using dissection microscopes. Identification Tags Every fish captured was fitted with at least one identification tag. Four different types of tags were used: cattle ear tags, placed in the caudal fin; dart tags, placed in the caudal fin; Monel clip tags, placed in the anterior of the dorsal fin; and Floy tags, attached at the base of the dorsal fin or in the caudal fin. No tag contacted another tag; this helped prevent tag wear, entanglement, and loss. Telemetry Telemetry transmitters were fitted to 5 fish in 1987 and 20 fish in 1990. Advanced Telemetry Systems (ATS - Isanti, MN) produced the transmitters in the 49 to 50 MHZ range. These transmitters were attached externally at the base of the dorsal fin with stainless steel cable and polyvinylchloride backing plates. Each transmitter was covered with water-

proof resin, weighed about 64 g, was 21 cm long, and had a 75-cm long antenna. Five transmitters were calibrated (pulse/minute) to detect water temperature in 1990. Signals produced by the transmitters were followed using a hand-held loop antennae from land or boat. In 1990, an automatic data logger was set near the mouth of the Sturgeon River. The logger, a receiver, battery, and Yagi antennae were set to receive signals continuously from 29 April to 8 July 1990. A single scan of all 20 channels on the receiver (one channel for each transmitter frequency) was set at 10 seconds. A total of 3.3 minutes was needed for a single serial scan of all 20 channels. Thuemler (1988) found 30 to 48-cm lake sturgeon moved downstream at 0.6 to 14.5 km/hour. Assuming a swimming speed of 0.8 km/hour it was expected that each fish with a transmitter would be detected about nine times as it passed the data logger (scan distance above and below the logger was about 183 m). Boat and lawnmower motors and CB radios interfered with some signals. When the transmitters attached to the lake sturgeon could no longer be heard near the spawning site, tracking began in the Portage Lake system. Tracking took place from small boats once or twice weekly, depending on weather, from late April through September 1990. Tracking in Keweenaw Bay was conducted aboard the R/V Navicula owned by Michigan Technological University. Transmittered lake sturgeon were located from this vessel on 14 occasions between 10 July and 27 September as it traveled through Portage Lake, the South Entry Canal, and Keweenaw Bay. To facilitate reporting the Portage Lake system was divided into five areas: 1) Portage Lake and the Sturgeon River mouth area, 2) Pike Bay, 3) the northwest arm of Portage Lake, 4) the northeast arm of Portage Lake, and 5) the south entry and the Sturgeon River Sloughs. Records were kept of the number of times a fish was located in each of these areas and in Keweenaw Bay. RESULTS Tag Retention From 1987 to 1994, 70 fish returned to the Sturgeon River spawning site bearing at least one of their original tags. Of the 70 fish, 51 were initially fitted with three tags each, either the combination cattle, Monel, and Floy or dart, Monel, and Floy (Table 1). Monel and Floy tags showed greatest re-

Movements, Population Characteristics, Lake Sturgeon TABLE 1. Total number of fish and number of tag returns of 51 lake sturgeon initially fitted with three tags at the Sturgeon River, Michigan spawning site, 1987 to 1994.

Returning Tag Combination All three Cattle/dart & Monel Cattle/dart & Floy Monel and Floy Cattle/dart only Floy only Monel only

Original tag combination Cattle, Dart, Monel, Monel, Floy Floy Total 2 2 4 0 1 1 2 1 3 8 10 18 1 2 3 10 5 15 5 2 7

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TABLE 3. Spawning periodicity of 86 tagged lake sturgeon recaptured once and 12 males recaptured twice at the Sturgeon River spawning site, 1987 to 1995. Number Male Female

1 0 0

Interval of Capture (Years) 2 3 4 5 6 24 30 27 14 3 0 2 5 3 1

7 0 1

terval was 2 to 4 years. The 12 females were recaptured after 3 to 7 years and the 74 males after 2 to 6 years. Sex Ratio

tention while dart and cattle tags placed in the caudal fin had the poorest retention. Arrival on Site and Homing From 1991 to 1995, when the hydroelectric facility operated near ROR, male and female lake sturgeon always appeared at the spawning site at the same time (Table 2). In most years at least one survey was made before any lake sturgeon appeared on site. Twenty-one lake sturgeon tagged in 1991 to 1993 were recaptured in the same section of the river in which they were initially captured and tagged. Two males were captured together in 1991, 1993, and 1995 when they returned to spawn. Spawning Periodicity From the spring of 1987 through the spring of 1995, 86 lake sturgeon returned to spawn 1 time, 12 females and 74 males, (Table 3) and 12 males returned 2 times. Of these 12 males the spawning in-

TABLE 2. Date and number of male and female lake sturgeon first seen at the Sturgeon River spawning site during years of near ROR operation, 1991 to 1995. Date 29 April 1991 4 May 1992 7 May 1993 4 May 1994 4 May 1995

Males 6 5 3 1 2

Females 11 4 3 1 2

The sex ratio of adult fish captured on the spawning grounds changed during the study. More males were observed during the years of peaking operation (1987 and 1988) than in years when flows were near ROR (1989 to 1995) (Table 4). During the years with most natural river flow (1991 to 1995) the sex ratio (male:female) at the spawning site ranged from 1.25:1 to 2.7:1. Incremental Growth and Age Data from 98 returning males was used to evaluate annual growth (Fig. 2). The average annual gain in length and weight increased with spawning interval for males. Average annual gains in length and weight of male lake sturgeon seem to be greatest in fish 130 to 149 cm long with spawning intervals of 3 to 4 years (Table 5). Greatest gains in length (1 to 8 cm) and weight (3 to 11 kg) for both sexes are summarized in Table 6. The return male spawners were all between 117 and 162 cm at first tagging. Yearly growth increments of 0.56, 0.26, 0.45, 0.71, and 0.61 cm and 0.07, 0.18, 0.23, 0.44, and 0.61 kg were calculated for males at large for 2, 3, 4, 5, and 6 years, respectively. The 12 females that returned to spawn after 3 to 7 years increased in length from 1 to 7 cm (mean, 2.2) and had weight changes of -3.6 to 10.9 kg (mean, 2.6). Length gain by females was similar to that shown in Figure 2 for males returning after similar periods but females gained 2 to 3 times more weight than males. The 249 female lake sturgeon captured at the Sturgeon River spawning site during the study averaged 153.4 cm and 25 kg and were usually larger than the 509 males captured at

286 TABLE 4.

Nancy A. Auer Sex ratio of lake sturgeon captured at the Sturgeon River spawning site, 1987 to 1995.

Male Female Undetermined Sex ratio

1987 48 12 19 4.1:1

1988 48 8 15 6:1

1989 34 17 7 2:1

1990 77 34 24 2.3:1

Year 1991 61 36 6 1.7:1

1992 65 52 4 1.25:1

1993 27 13 2 2.1:1

1994 65 42 5 1.5:1

1995 85 32 8 2.7:1

TABLE 6. Largest gains in length and weight by spawning interval for lake sturgeon recaptured at the Sturgeon River spawning site, 1987 to 1995.

Male Female Male Female Male Female Male Female

FIG. 2. Mean annual growth in length (cm) and weight (kg) for 98 male lake sturgeon returning to spawn at Sturgeon River Michigan site after 2 to 5 years. All fish were 117 to 155 cm at first capture. the site, which averaged 134.5 cm and 14 kg (Fig. 3). Ages from 12 fin ray samples (Table 7) showed Sturgeon River females between 145 and 160 cm to be 30 to 38 years old, whereas males between 120 and 135 cm were 20 to 30 years old.

Spawning interval (yrs) 3 3 4 4 5 5 6 7

Weight gain (kg) 5.2 2.7 5.4 10.9 4.1 5 4.1 3.2

Length gain (cm) 2 1 6 2 8 7 7 3

Post-Spawning Movements In 1987 the Prickett hydroelectric facility operated in a peaking mode. Three males and two females fitted with transmitters between 22 and 25 April left the spawning site between 20 and 31 May and were located in Portage Lake until 20 June

TABLE 5. Mean change in length (cm) and weight (kg) of male lake sturgeon at the Sturgeon River spawning site, by length-frequency interval. Total number of fish in parentheses. Length interval (cm) Spawning interval (years) 2 3 4 5

120–129 2 (2) 0 1 (5) 0 2 (5) 0.9 3 (8) 2.4

130–139 1 (8) 0.4 1 (11) 1.2 3 (10) 1.8 4 (4) 2.0

140–149 150–159 1 (11) 1 (3) 0.1 0 1 (11) 0 (3) 0.7 0 1.5 (11) 0.5

FIG. 3. Length-frequency distributions for 758 adult lake sturgeon captured at the Sturgeon River, Michigan spawning site, 1987 to 1995.

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TABLE 7. Ages (years) of lake sturgeon taken at the Sturgeon River spawning site. Ages were determined from cross sections of pectoral fin rays by three independent viewers. Fish number 1 2 3 4 5 6 7 8 9 10 11 12

Date of collection 21-4-87 22-4-87 24-4-87 25-4-87 25-4-87 26-4-87 27-4-87 27-4-87 28-4-87 29-4-87 5-5-87 24-4-90

Sex ?M ?F F M M ?M F F M M F F

Length (cm) 126 145 161 132 132 122 150 144 137 152 157 144

1987 (Table 8). The males stayed near the river mouth and slough area until 10 June and then began to disperse. Females were first located in Pike Bay and Portage Lake north of the Sturgeon River mouth on 15 June; neither female showed much movement and tracking was discontinued on 20 June 1987. In 1990, 12 females, 7 males and 1 fish of undetermined sex were fitted with transmitters (Table 9). None of these fish remained at the spawning site or in the river. Thirteen fish left the river within 9 days, and two others left after 16 and 54 days (Table 9). Signals from fish #20 were never heard and the transmitter on fish #8 is believed to have fallen off at the spawning site. Signals from three other fish did not register on the data logger but these fish were later located in the Portage Lake system (Table 9). Of 18 trackable fish, #7 remained in the river 54 days and later died during the study and #4 was located only once. This male, minus the

Weight (kg) 10 19 27 11 11 9 23 18 13 24 — 22

1 19 31 25 23 21 24 30 — 30 — 38 —

Viewer 2 23–24 31 32 27 22-24 26 34 34 33 28-30 32-36 —

transmitter, returned to spawn in the spring of 1992. Four others, fitted with transmitters in 1990, returned to spawn without the transmitters, #9 and #13 in 1994 and #5 and #6 in 1995. The transmitter attachment sites on these fish had completely healed. Sixteen fish were tracked until 27 September 1990. These fish exhibited several different patterns of movement. Most fish located near the Sturgeon River mouth either moved out the natural river mouth and into Portage Lake or moved through the “cut” and into Pike Bay. At least seven fish used the “cut” and spent from mid-May to early June in Pike Bay. The other nine fish passed out the natural river mouth into Portage Lake, but three of them later moved into Pike Bay. Tracked fish showed no coherent pattern of movement in the Portage Lake system after leaving the Sturgeon River. Nine fish first spent 3 to 53 days (mean, 22) in Pike Bay immediately after spawning. Obvious differences in

TABLE 8. Date of tagging, date last heard at Sturgeon River spawning site, and first location in the Portage Lake (PL) system for five lake sturgeon fitted with telemetry transmitters in 1987. Fish number 1 2 3 4 5

Sex M F M F M

Date tagged 22/4 22/4 23/4 24/4 25/4

3 25 38 29 28 21 26 30 34 31 27 32 30

Date left site 20/5 29/5 31/5 29/5 22/5

Date located in PL 3/6 31/5 15/6 15/6 5/6

Days from site to PL 14 3 16 18 14

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Nancy A. Auer TABLE 9. Tagging and location information for 20 lake sturgeon fitted with transmitters in 1990 at the Sturgeon River, Michigan spawning site. PL = Portage Lake, KB = Keweenaw Bay, TL = Torch Lake, DY = Day of the year. Max. no. DY last days on DY and area Fish DY heard at DY passed spawning of last number Sex tagged Prickett data logger site location 1 M 115 119 121 4 270 PL 2 F 132 136 142 4 175 * TL 3 F 114 118 120 4 270 PL 4 M 117 119 121 2 146 PL 5 M 115 119 122 4 198 PL 6 F 118 134 137 16 270 KB 7 F 114 167 176 54 158 ** TL 8 F 167 — —— — * 9 M 115 120 135 5 227 NW PL 10 F 135 138 — — 242 KB 11 M 138 147 149 9 267 TL 12 ? 123 123 147 1 176 * 13 M 124 153 — — 270 KB 14 F 135 153 — — 270 PL 15 F 135 138 140 3 270 PL 16 F 135 140 144 5 270 SE PL 17 F 138 138 147 1 270 PL 18 M 121 122 141 2 249 PL 19 F 117 118 120 2 198 NW PL 20 F 117 118 — — *** *tag fell off after this date, all further locations in same area,** fish found dead,*** transmitter signal never detected.

movement of male and female fish were not observed. Nine lake sturgeon with telemetry transmitters located in late August and September 1990 had moved 75 to 97 km from the spawning site and an additional 5 to 27 km from the shallow river mouth area. Data on water temperature, obtained from four of the five fish wearing temperature sensitive transmitters, showed they stayed in the Portage Lake area. In May they were found in water at 10 to 19°C, in June at 15 to 21°C, in July at 18 to 24°C, in August at 15 to 24°C, and in September at 16 to 19°C. Range of Sturgeon River Spawners Lake sturgeon tagged at the Sturgeon River spawning site, or their tags, were recovered by commercial, Native American, and sport fishermen throughout the study. Lake sturgeon that spawned in the Sturgeon River were recovered as far away as 230 km to the east and 280 km to the west from the spawning site (Fig. 4). Males were commonly en-

countered in Lake Superior in lower Keweenaw Bay (100 km) whereas females were recovered from Misery Bay (140 km), Bete Grise Bay (130 km), and Munising Bay (230 km). A cattle tag, from a female tagged at the Sturgeon River spawning site on 19 May 1989, was snagged on a trap net set and recovered by commercial fishermen 43 days later (1 July 1989) in Munising Bay, Lake Superior (230 km). Tags from 35 fish were returned; 15 were from commercial, 15 from Native American, and 6 from sport fishermen. Sport fishermen commonly caught lake sturgeon in the Sturgeon River or near its mouth during post-spawning migration. Native American and commercial fishermen using gill, pound, and trap nets set at 9 to 30 m captured 30 lake sturgeon in Southern Lake Superior (Fig. 4). One male caught in lower Keweenaw Bay in 1987 was recaptured in Bete Grise Bay in 1993. During the study two fish, first tagged near Bayfield, Wisconsin by Wisconsin Department of Natural Resources personnel, were captured at the

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FIG. 4. Lake sturgeon tag returns from incidental, commercial and Native American catches in the waters of Lake Superior, 1987 to 1994. Number 1 = 1 female and 1 undetermined sex, 2 = 2 undetermined sex, 3 = 11 males, 2 females and 1 undetermined sex, 4= 2 males and 1 female, 5 = 2 males and 8 females, 6 = 4 males and 1 female. Sturgeon River spawning site. A third fish from the Bayfield area was captured in a pound net in 1994 in Misery Bay, along with a lake sturgeon first tagged at the Sturgeon River spawning site. Two males initially tagged at the Sturgeon River site were also recovered in the Bayfield, Wisconsin area, 280 km to the west. DISCUSSION Several of the findings from this study differ from those reported in previous research. Prior studies on spawning lake sturgeon suggest that male lake sturgeon reach the vicinity of the spawning grounds before females (Harkness and Dymond 1961, Lyons and Kempinger 1992, Priegel and

Wirth 1997). Folz and Meyers (1985), Lyons and Kempinger (1992), and Priegel and Wirth (1977), working in the Wolf River, Wisconsin reported male sturgeon on the spawning site before female fish. Females, usually larger and heavier than males, may remain near the middle and bottom of the Wolf River, Wisconsin, thus avoiding capture and observation by those using dip-nets along the river banks. Sturgeon are believed to imprint (Boiko 1993) and home to specific and historic sites to spawn (Dadswell 1979, Lyons and Kempinger 1992). Dadswell (1979) suggests that pairs of shortnose sturgeon (A. brevirostrum) in the St. John’s River, New Brunswick may actually bond. He observed fish, tagged at the same location and date returning

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together to that location in a following year. Homing appears to occur at the Sturgeon River spawning site, as evidenced by fish returning to spawn in the same locations and with cohorts from previous years. Sex ratios reported in many lake sturgeon studies are close to 1:1 but usually these data are from sport or commercial catches (Dumont et al. 1987, Fortin et al. 1993, Haugen 1969, Nowak and Jessop 1987, Schneberger and Woodbury 1944, Threader and Brousseau 1986). Only three studies report sex ratios of lake sturgeon at spawning sites. Roussow (1957) found a 1:1.06 male to female ratio for lake sturgeon caught in June on the Ottawa River. Folz and Meyers (1985) reported a male:female sex ratio of 5.7:1 for a Wolf River, Wisconsin spawning site from 1975 to 1983. Lyons and Kempinger (1992) reported an even greater ratio of 8.5:1 and 9.6:1 for fish captured on the Wolf River and Fox River spawning sites from 1954 to 1984. These investigators felt that a shorter interval between spawnings for males resulted in a greater number of males encountered each spawning. Larger, heavier females may not have been represented in the sampling effort at the spawning site because capture took place from the river bank with dip-nets. Because the Lake Winnebago system is managed for a spear fishery (Folz and Meyers 1985), the larger females are believed to also be experiencing greater mortality (Probst and Cooper 1955, Lyons and Kempinger 1992). The male:female sex ratio of 1:1 to 3:1 at the Sturgeon River spawning site is similar to ratios observed in natural, unexploited populations. Early research (Harkness and Dymond 1961) suggested that lake sturgeon did not spawn every year; females were thought to spawn every 4 to 7 years and males every 2 years. Priegel and Wirth (1977) found females spawned every 4 to 6 years in Lake Winnebago, and recent work by Lyons and Kempinger (1992) indicates that male lake sturgeon commonly spawn annually or biennially and females every 3 to 4 years. The intervals between spawning observed for Lake Winnebago fish are shorter than those seen for Sturgeon River fish and may reflect conditions of warmer water, faster growth and maturation, or possible density dependent maturation as a result of numerous fish in confined conditions in the Lake Winnebago system. Growth increments for returning male spawners in the Sturgeon River are some of the first growth data for unrestricted adult lake sturgeon in Great Lakes systems. Growth in length appears to decrease with age in lake sturgeon while growth in

weight increases with age (this study, Harkness 1923, Priegel and Wirth 1977, Sandilands 1987). Slade and Auer (1997) applied age data, collected from lake sturgeon stocked into western Lake Superior, to the average length frequencies of lake sturgeon observed in the Sturgeon River study and suggest that Sturgeon River males may be 22 years of age at 134 cm and females about 30 years at 153 cm. These estimates closely agree with data collected from 12 fish in the Sturgeon River in 1987 and 1990. Sturgeon River fish are older than fish of similar lengths from the Lake Winnebago system. Folz and Meyers (1985) determined Lake Winnebago males are 17 years old at 134 cm and females are 23 years old at 153 cm. Lake Winnebago males were 17 years old at 134 cm and females were 30 years old at 153 cm (Schneberger and Woodbury 1944). St. Lawrence River lake sturgeon seldom exceeded 150 cm, those about 134 cm were 25 to 28 years of age (Fortin et al. 1993). Most fish captured in the St. Lawrence River were between 92 and 105 cm and were thought to be 15 to 20 years old. Ages of lake sturgeon in the Sturgeon River closely match those of lake sturgeon in the South Saskatchewan River, Alberta (Haugen 1969); they also are similar to confined populations in the Menominee and Flambeau rivers, Wisconsin where lake sturgeon 135 cm and 153 cm are 27 and 32 to 38 years old (Priegel 1973) or 29 and 40 years old (Scholl 1986). Sturgeon River fish may be older than Lake Winnebago system fish because of lower water temperatures in the Lake Superior system or effects of past water level manipulation by the hydroelectric facility in the Sturgeon River prior to 1990. After spawning in the Sturgeon River, lake sturgeon moved quickly out of the river system, particularly in the years the hydroelectric facility began to operate at near ROR (Auer 1996). Quick downstream, post-spawning movement has been noted for the Sevryuga sturgeon, A. stellatus (Shubina 1971) in the Volga River; shortnose sturgeon, A. brevirostrum in the Savannah River (Hall et al. 1991), Delaware River (O’Herron et al. 1993), and Merrimack River (Kieffer and Kynard 1993), and for lake sturgeon in the Wisconsin River (Larson 1988) and Wolf River (Lyons and Kempinger 1992). Two lake sturgeon moved from the southern end of Lake Winnebago, spawned at the Wolf River spawning site, and returned to the southern end of the lake, covering 456 km in 31 days. Of 133 fish captured at the Wolf River site, 132 were recap-

Movements, Population Characteristics, Lake Sturgeon tured 6 months later in Lake Winnebago (Lyons and Kempinger 1992). Lake sturgeon in the Sturgeon River and in other systems do not remain in the river after spawning. Rapid downstream movement may be necessary to avoid stranding, exposure to direct sunlight, and predators as spring river flows decline, and to find food and rest. This may be an adaptation that removes feeding adults from areas where eggs and newly-hatched young are concentrated. Lake sturgeon can survive when confined within river systems (Nowak and Jessop 1987, Thuemler 1985) but size of individuals as well as entire stock potential can be less than that of groups with access to large lake and river areas for feeding and spawning. The work of Rien and Beamesderfer (1994) and Galbreath (1985) show dramatic differences in growth between impounded and free-ranging stocks of white sturgeon in the Columbia River, Washington. Sturgeon having unlimited range grow at constant and greater rates than those confined by dams in that system. Confined stocks are also at risk of extirpation from disease, impacts of pollution, or natural catastrophic events. Little information exists on the extent of lake sturgeon movements. Dumont et al. (1987) noted that lake sturgeon tagged on spawning grounds in the St. Lawrence River showed lengthy movements after spawning. Fortin et al. (1993), working in the same system, noted spawning migrations were extensive, but most lake sturgeon tagged in lakes remained in the lake. Lyons and Kempinger (1992) found lake sturgeon moved extensively in Lake Winnebago, which has a surface area of 558 km2, but fish in this system are prevented from moving into Green Bay or Lake Michigan by dams on the Fox River. In 41 km 2 Black Lake, HayChmielewski (1987) found lake sturgeon in June, July, and August moved 1,500 to 2,500 m daily. This inland lake population is also blocked from the Great Lakes by a dam. Telemetry tracking and tag return information from lake sturgeon in southern Lake Superior indicated that this species may congregate at certain locations or use specific travel routes. Male lake sturgeon from the Sturgeon River were commonly captured in lower Keweenaw Bay, whereas larger female fish were recovered in Munising Bay, Bete Grise, and Misery Bay. Fortin et al. (1993) noted similar behavior for lake sturgeon in the St. Lawrence River, finding non-spawning lake sturgeon occured at very localized sites. Knowledge of such concentrating behavior will be critical to man-

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agement and recovery efforts. Commercial and sport fishers may focus fishing effort in areas of these concentrations or along paths of migration and quickly deplete stocks. Lake sturgeon appear to “home” not only in pre-spawning migrations but perhaps to post-spawning feeding and over-wintering sites as well. If they segregate by sex, commercial harvest in “homing” locations could devastate stocks. Lake sturgeon tagged in the Sturgeon River have been recovered near Ashland, Wisconsin. These fish are exposed to less protection while in Wisconsin waters because the state does not consider this species to be threatened or endangered. This long-term study of an unrestricted lake sturgeon population in the Sturgeon River revealed some important population characteristics different from those seen in previous studies. Male and female lake sturgeon spawning in the Sturgeon River appear on site together, have a male:female sex ratio between 1:1 to 3:1, and move quickly out of the river after spawning. River fidelity is high and spawning intervals are longer than those observed for restricted stocks. Lake sturgeon from the Sturgeon River use migration corridors and appear to separate by sex to feeding and resting areas in Lake Superior. The re-establishment of stocks of lake sturgeon throughout the Great Lakes will depend on recognizing the importance of and protecting small spawning sites, open migration corridors, and segregation and homing of sexes to resting and feeding areas. ACKNOWLEDGMENTS This project would not have been possible without assistance from many volunteers, to whom I am indebted. E. Lutz and D. Rees assisted in telemetry tracking in 1990. The work could not have been accomplished without the cooperation of Advanced Telemetry Systems, the Michigan Department of Natural Resources, and the Upper Peninsula Power Company. Funding was received from the Michigan Sea Grant College Program, Michigan Department of Natural Resources Nongame and Living Resources Small Grants Program, Ottawa National Forest, Michigan Technological University, and the Upper Peninsula Power Company. The publication of this paper is funded through the J. Frances Allen Scholarship awarded by the American Fisheries Society. This paper was submitted in partial fulfillment of a Doctor of Philosophy degree at Michigan Technological University. I wish to thank committee members: Dr. Stephen H. Bowen, Dr. Robert E.

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