**4. Lake sturgeon movements**

382 Modern Telemetry

16m depth 1m depth

Fig. 9. Digital elevation model of Fig. 10. Depth availability in Round Lake

Hardness = 150 (Rock) Hardness = 95 (Clay)

Percent of total available habitat

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Depth of Lake (m)

95 105 115 125 135 145 155 165 Substrate Hardness

Fig. 11. Hardness map of Pigeon River at Fig. 12. Hardness (substrate) availability in

*Substrate and Depth***:** Maximum depth of Round Lake is 16m. A depth map of Round Lake is shown in Fig. 9**.** Two deep holes, one off the Northeast corner of each island, are found in the lake. The general structure is bowl shaped. Depth availability is shown in Fig. 10. Two and three meters depths are available 33 and 16% respectively. Seven, 8, and 9 meter depths

0

5

1 0

1 5

Percent of total Availability

2 0

2 5

3 0

Substrate hardness of the lake is shown in Fig. 11. Substrate was generally related to depth. The deeper areas of the lake had softer substrates with a high percentage of silt. The shallow sections along the shoreline to about 10m depth had sandy substrates. Cobble and rock substrate predominated in areas of high flow at the inlet and outlet. Availability of substrate hardness was 11, 25, and 17 percent for hardness values of 125 (coarse sand), 130 (gravel),

Round Lake obtained from sonar data. Round Lake.

are available 5, 6, and 8% respectively.

Round Lake.

The biological data for the nine lake sturgeon tagged with acoustic tags are listed in Table 2. The nine fish were tracked for 27 days and 15,446 locations were obtained. Movements ranged from individuals that were mostly sedentary to highly mobile individuals. Daily movements were variable between fish as well as by the same fish on different days. Figure 13 shows the locations of fish 4015 on four separate days. Movement was confined to the inlet to Round Lake on day 210. Movement increased on days 211 and 212 and covered most of the lake. Movement on day 220 was restricted to the river outlet.

A comparison of the movements of juvenile and adult lake sturgeon is shown in Fig. 14. Movements of the juvenile fish were focused at the inlet and outlet and in the deep hole (~16 m). Movements of the subadult and adult lake sturgeon were also associated with the inlet and outlet but the movements were more widespread around the lake. The channel where water entered the lake was a preferred site as was the outlet from the lake. Figure 15 shows the swimming depth of sturgeon 4014 on day 206 relative to the bottom depth. Note the day 206 is based on January 1 being day 1. Sturgeon 4014 was on the bottom 30% of all locations on day 206. During the hours from midnight to 5 AM sturgeon 4014 was in the water column the majority of the time. From 5 AM to 11 PM more time was spent on the bottom. After 11 PM lakes sturgeon movements shifted to the water column. Figure 16 shows sturgeon 4015 on day 221 where 53% of all locations were on the bottom on day 221. Sturgeon 4017 on day 211 was on the bottom for the entire day but periodically swam to the surface (Fig. 17**).** Figure 18 shows the overall distribution of each lake sturgeon fitted with a pressure tag and the total distribution of all fish on the bottom and in the water column.

Movements and Habitat Use by Lake Sturgeon (*Acipenser fulvescens*)

Swimming Depth Bottom Depth

sturgeon 4014 on day 206. day 221.

6 134 258 414 545 719 824 1000 1148 2149 2321 Time








Depth (m)



0

Depth (m)

in an Unperturbed Environment: A Small Boreal Lake in the Canadian Shield 385

Fig. 15. A comparison of swimming depth Fig. 16. A comparison of swimming depth and and bottom depth of the lake for bottom depth of the lake for sturgeon 4014 on

> Swimming Depth Bottom Depth


Depth (m)

Fig. 17. A comparison of swimming depth Fig. 18. Time spent in the water column and on and bottom depth of the lake for the lake bottom for sturgeon 4014, 4015 and

sturgeon 4017 on day 211. 4017 combined total.

1 31 63 91 120 144 175 2046230 Tim

Percent of total locations

4014(206) 4015(210) 4017(206) 4017(219) Lake Sturgeon (day)

% on the bottom % in the water column

Swimming Depth Bottom Depth

6 134 258 414 545 719 824 1000 1148 2149 2321 Time

Fig. 13. Movements of lake sturgeon 4015 on four separate days.

Fig. 14. Comparison of the movements of adult and juvenile sturgeon in Round Lake

A) Fish 4015, Day 210 C) Fish 4015, Day 212

B) Fish 4015, Day 211 D) Fish 4015 Day 220

Fig. 13. Movements of lake sturgeon 4015 on four separate days.

Fig. 14. Comparison of the movements of adult and juvenile sturgeon in Round Lake

Adult Fish Juvenile


sturgeon 4014 on day 206. day 221.

Fig. 15. A comparison of swimming depth Fig. 16. A comparison of swimming depth and and bottom depth of the lake for bottom depth of the lake for sturgeon 4014 on

sturgeon 4017 on day 211. 4017 combined total.

Fig. 17. A comparison of swimming depth Fig. 18. Time spent in the water column and on and bottom depth of the lake for the lake bottom for sturgeon 4014, 4015 and

Movements and Habitat Use by Lake Sturgeon (*Acipenser fulvescens*)

in an Unperturbed Environment: A Small Boreal Lake in the Canadian Shield 387

A) 4014, day B) 4014, night

C) 4015, day D) 4015, night

Fig. 19. Day and night comparison of time spent at the surface for sturgeon 4014, 4015, and

E) 4017, day F) 4017, night

4017.

Figure 20 shows substrate selection of sturgeon 4014, 4015, 4017 from the 7 day sample. Substrate with a hardness value of 110 was selected 53% of all locations.

Overall, lake sturgeons were located on the bottom 39% and in the water column 61% of the locations on the 7 day sample (day 215 based on January 1 being day 1).

The amount of time spent at the surface varied with time of day. The majority of locations < 1m occurred between the hours of 8 PM and 8 AM (Fig. 19).

The selection of depth was analysed from two perspectives**.** Figure 21 shows the overall depth selection of the three lake sturgeon tagged with depth tags. Thirty percent of all locations were less than two meters. Sixty-six percent were less than four meters. Figure 22 shows the depth selection of the three lake sturgeon including only the locations in which they were in contact with the substrate during the 7 day sample. Seven, 8, and 9 meter depths were selected 11, 31, and 21 percent respectively. Figure 23 shows movements of lake sturgeon 4014. It spent 70% of the time in the water column at the inlet on day 206 and on day 221 lake sturgeon 4014 spent 47% of the time in the water column.

Figure 24 shows movements of lake sturgeon 4015 on day 210. It spent 59% of its time in the water column at the inlet of the river. Lake sturgeon 4017 (Fig. 25) spent 60% of the time in the water column on days 206 and 222, 25% on day 211, and 88% on day 219. On days 211 and 219, sturgeon 4017 covered most of lake, including areas around the inlet and outlet.

The use of depth tags eliminates the guess work of whether a fish was on the bottom or in the water column at each position. Comparisons were made in this study among telemetry position, depth and substrate using data from depth tags. Substrate, depth and current were the three primary environmental variables measured.

Lake sturgeon movements ranged from sedentary to highly active. Movements in the areas of the inlet and outlet, areas of higher flow rate were quite common as well as movements in the deeper areas and along the natural flow of the river. Movements along the shorelines were rare. Along the shorelines the water is shallow, there is little flow, and the substrate is primarily sandy. Movements of smaller and larger fish were similar but larger fish moved greater distances. Nevertheless, juvenile fish appear to use most of the same habitat as the larger fish. Movements for both were related to the inlet and outlet and the deeper part of the lake.

The larger lake sturgeon spent a significant amount of time in the water column and at the surface. We do not know what juveniles were doing concerning depth selection because they were too small to be fitted with tags with pressure sensors. The amount of time in the water column by the larger fish suggests these fish were feeding on organisms drifting with the current. A majority of the records on movement were near the inlet and outlet where drift nets recovered insects and the occasional small fish.. Extensive lake sturgeon activity was noted where insects were carried by the current, were floating on the surface, or were emerging i.e. mayflies. High sturgeon activity in some areas was also correlated with clam beds.

The timing of movements in the water column and at the surface was correlated to light intensity. Lake sturgeon spent more time at the surface at night than during the day, when more time was spent on the bottom.

Based on the comparison of substrate selection and substrate availability lake sturgeon were found over fine sand, cobble, and rock substrate at higher frequencies than the proportion of this substrate in the lake. Coarse sand and gravel substrates were selected at a lower frequency than their proportions in the lake.

Figure 20 shows substrate selection of sturgeon 4014, 4015, 4017 from the 7 day sample.

Overall, lake sturgeons were located on the bottom 39% and in the water column 61% of the

The amount of time spent at the surface varied with time of day. The majority of locations

The selection of depth was analysed from two perspectives**.** Figure 21 shows the overall depth selection of the three lake sturgeon tagged with depth tags. Thirty percent of all locations were less than two meters. Sixty-six percent were less than four meters. Figure 22 shows the depth selection of the three lake sturgeon including only the locations in which they were in contact with the substrate during the 7 day sample. Seven, 8, and 9 meter depths were selected 11, 31, and 21 percent respectively. Figure 23 shows movements of lake sturgeon 4014. It spent 70% of the time in the water column at the inlet on day 206 and on

Figure 24 shows movements of lake sturgeon 4015 on day 210. It spent 59% of its time in the water column at the inlet of the river. Lake sturgeon 4017 (Fig. 25) spent 60% of the time in the water column on days 206 and 222, 25% on day 211, and 88% on day 219. On days 211 and 219, sturgeon 4017 covered most of lake, including areas around the inlet and outlet. The use of depth tags eliminates the guess work of whether a fish was on the bottom or in the water column at each position. Comparisons were made in this study among telemetry position, depth and substrate using data from depth tags. Substrate, depth and current were

Lake sturgeon movements ranged from sedentary to highly active. Movements in the areas of the inlet and outlet, areas of higher flow rate were quite common as well as movements in the deeper areas and along the natural flow of the river. Movements along the shorelines were rare. Along the shorelines the water is shallow, there is little flow, and the substrate is primarily sandy. Movements of smaller and larger fish were similar but larger fish moved greater distances. Nevertheless, juvenile fish appear to use most of the same habitat as the larger fish. Movements for both were related to the inlet and outlet and the deeper part of

The larger lake sturgeon spent a significant amount of time in the water column and at the surface. We do not know what juveniles were doing concerning depth selection because they were too small to be fitted with tags with pressure sensors. The amount of time in the water column by the larger fish suggests these fish were feeding on organisms drifting with the current. A majority of the records on movement were near the inlet and outlet where drift nets recovered insects and the occasional small fish.. Extensive lake sturgeon activity was noted where insects were carried by the current, were floating on the surface, or were emerging i.e. mayflies. High sturgeon activity in some areas was also correlated with clam

The timing of movements in the water column and at the surface was correlated to light intensity. Lake sturgeon spent more time at the surface at night than during the day, when

Based on the comparison of substrate selection and substrate availability lake sturgeon were found over fine sand, cobble, and rock substrate at higher frequencies than the proportion of this substrate in the lake. Coarse sand and gravel substrates were selected at a lower

Substrate with a hardness value of 110 was selected 53% of all locations.

locations on the 7 day sample (day 215 based on January 1 being day 1).

day 221 lake sturgeon 4014 spent 47% of the time in the water column.

the three primary environmental variables measured.

the lake.

beds.

more time was spent on the bottom.

frequency than their proportions in the lake.

< 1m occurred between the hours of 8 PM and 8 AM (Fig. 19).

Fig. 19. Day and night comparison of time spent at the surface for sturgeon 4014, 4015, and 4017.

Movements and Habitat Use by Lake Sturgeon (*Acipenser fulvescens*)

selection of lake sturgeon 4014. sturgeon 4015.

Unknown Depth On the bottom In the water column

Fig. 25. Movements and depth selection of lake sturgeon 4017.

in an Unperturbed Environment: A Small Boreal Lake in the Canadian Shield 389

Fig. 23. Movements and depth Fig. 24. Movements and depth selection of lake

Unknown Depth On the bottom In the water column **25** 

**23** Unknown depth

On the bottom In the water column **24** 

Fig. 20. Substrate selection by lake sturgeon in Round Lake (see Table 3)

sturgeon in Round Lake. in contact with the substrate.

Fig. 21. Overall depth selection by lake Fig. 22. Depth selection by lake sturgeon when

*Hexagenia* (Ephemeridae) is a common prey item of lake sturgeon and silt and clay substrates are the preferred habitats. By contrast clams were often found in sandy substrates. While invertebrates were not common in the sieved substrates mayflies are a major food source for most fish species in the lake. Similarly, mayflies were a major food item of lake sturgeon, based on stomach contents which was verified by gavage. It appears in this system that mayflies are a major food source but competition for this food source by most fish species in the lake may make this food item a potentially limiting factor. Similar observations have been reported by others (Choudhury et al.. 1995; Chiasson et al. 1997).

The selection of depth based on horizontal and vertical movements of lake sturgeon seems to be related to current. Lake sturgeon tended to stay in the water column more often in areas of high flow such as the inlet and outlet. Since the study took place in mid summer and this activity was not related to spawning behaviours or movement related to fall/winter migrations the majority of movements are likely related to feeding behaviour.

selection of lake sturgeon 4014. sturgeon 4015.

Fig. 20. Substrate selection by lake sturgeon in Round Lake (see Table 3)

95 100 105 110 115 120 125 130 135 140 145 Substrate Hardness

0

50

100

150

Frequency of selection

200

250

300

Fig. 21. Overall depth selection by lake Fig. 22. Depth selection by lake sturgeon when

*Hexagenia* (Ephemeridae) is a common prey item of lake sturgeon and silt and clay substrates are the preferred habitats. By contrast clams were often found in sandy substrates. While invertebrates were not common in the sieved substrates mayflies are a major food source for most fish species in the lake. Similarly, mayflies were a major food item of lake sturgeon, based on stomach contents which was verified by gavage. It appears in this system that mayflies are a major food source but competition for this food source by most fish species in the lake may make this food item a potentially limiting factor. Similar observations have been reported by others (Choudhury et al.. 1995; Chiasson et al. 1997). The selection of depth based on horizontal and vertical movements of lake sturgeon seems to be related to current. Lake sturgeon tended to stay in the water column more often in areas of high flow such as the inlet and outlet. Since the study took place in mid summer and this activity was not related to spawning behaviours or movement related to fall/winter

sturgeon in Round Lake. in contact with the substrate.

migrations the majority of movements are likely related to feeding behaviour.

Fig. 23. Movements and depth Fig. 24. Movements and depth selection of lake

Fig. 25. Movements and depth selection of lake sturgeon 4017.

Movements and Habitat Use by Lake Sturgeon (*Acipenser fulvescens*)

in an Unperturbed Environment: A Small Boreal Lake in the Canadian Shield 391

The stick ship tract directly below illustrates the ship tract across the river (red) and the blue lines shows relative current flows and direction along the transect. The top of the ship tract is the right side looking downstream, unless otherwise described. Figure 27 (transect 1**)** has a current ranging from 0.250-1.0 m/sec and while lake sturgeon moved through this area they spent most of their time on the right side in back eddies separated from the main flow by a ridge on the bottom. The current in this area was between 0.25 and 0.750 m/sec. In the area of transect 2 (Fig. 26B) lake sturgeon moved through this region but did not remain in the area. The strongest current encountered throughout this section of the Pigeon River was up to 2 m/sec. The river was shallow about 1.5 m at the narrowest section of the river with turbulence and air bubbles (the reason for the large numbers of blank spaces i e. no data).

Fig. 27. Pigeon River ship transect 1 Fig. 28. Pigeon River ship transect 8

The current was slightly lower on the left side (looking downstream) and deeper but this was off the main flow. Transects 7, 8 and 9 are from a region of the river where considerable lake sturgeon activity was recorded **(**Fig. 14). It is apparent from the boat track of Fig. 28 that a small back eddy occurs on the right side (looking downstream). From the acoustic tag data there was extensive movement throughout this area indicating that lake sturgeon movements in currents up to 1 m/sec were routine. Figure 29 illustrates a transect from a region of Round Lake with high lake sturgeon activity and where currents ranged from 0.00 to 0.250 m/sec. Transects 15 (Fig.26B) represents an area of Round Lake where flow from the river entering Round Lake starts to slow. Most of the current in the river bed is 0.5 m/sec. Figure 30 (transect 16) illustrates the river bottom and shallow area with macrophytes on the right side. Macrophytes have a similar affect on the equipment as air bubbles and as result the quality of the data is reduced. From the ship track in transect 16

(see Fig. 26B). (see Fig. 26B).
