**5. Current profiling**

Since lake sturgeon movements and substrate were being evaluated in Round Lake and there was evidence that currents had a role in their distribution we evaluated current distribution in the lake. Figure 26A illustrates the cross sections of the river and lake where data was collected for current profiling and Fig. 26B identifies transects for which data was presented and discussed in the text.

Current profiling was done with the RDI Workhorse (Acoustic Doppler Current Profiler). This system was initially designed for stationary applications but its use was broadened to include total discharge measurements of streams and rivers and to measure currents in the areas where fish moved. This can be done from small moving boats.

Fig. 26. Transects for the current profile measurements in the Pigeon River at Round Lake. A) all transects throughout the lake and B) includes transects where current profiles are presented in this report with additional transects and current profiles also shown tagged lake sturgeon where in these areas for extended periods of time. Red dots = location of radio tagged lake sturgeon

Data collection focused in the areas of greatest activity in the Pigeon River in and around Round Lake because lake sturgeon tagged with radio and sonar tags moved short distance upstream to Grant Falls and downstream to the second rapids (Fig. 26A).

Current profiles: Current profiles were taken in 1997, 2000, 2001. Movements of lake sturgeon in regions of the Pigeon River above and below Round Lake were determined with radio tags and sites where more transects were run are illustrated in Fig. 26A. Figure 26B outlines selected cross sections, some of which are discussed below. The current cross sections shown in Fig. 27 is above the second rapids on the Pigeon River downstream of Round Lake and the graph below the velocity magnitude is the boat or ship track that also indicates the direction and relative magnitude of the current**.** Note current is measured across a body of water and in the water column in units referred to as cells. The cells are coloured and represent the current in a cell. Each cell is coloured in the graph (see velocity magnitude) and is ~20 cm but cell size may vary depending on depth at the sampling point.

Since lake sturgeon movements and substrate were being evaluated in Round Lake and there was evidence that currents had a role in their distribution we evaluated current distribution in the lake. Figure 26A illustrates the cross sections of the river and lake where data was collected for current profiling and Fig. 26B identifies transects for which data was

Current profiling was done with the RDI Workhorse (Acoustic Doppler Current Profiler). This system was initially designed for stationary applications but its use was broadened to include total discharge measurements of streams and rivers and to measure currents in the

Fig. 26. Transects for the current profile measurements in the Pigeon River at Round Lake. A) all transects throughout the lake and B) includes transects where current profiles are presented in this report with additional transects and current profiles also shown tagged lake sturgeon where in these areas for extended periods of time. Red dots = location of radio

Data collection focused in the areas of greatest activity in the Pigeon River in and around Round Lake because lake sturgeon tagged with radio and sonar tags moved short distance

Current profiles: Current profiles were taken in 1997, 2000, 2001. Movements of lake sturgeon in regions of the Pigeon River above and below Round Lake were determined with radio tags and sites where more transects were run are illustrated in Fig. 26A. Figure 26B outlines selected cross sections, some of which are discussed below. The current cross sections shown in Fig. 27 is above the second rapids on the Pigeon River downstream of Round Lake and the graph below the velocity magnitude is the boat or ship track that also indicates the direction and relative magnitude of the current**.** Note current is measured across a body of water and in the water column in units referred to as cells. The cells are coloured and represent the current in a cell. Each cell is coloured in the graph (see velocity magnitude) and is ~20 cm but cell size may vary depending on depth at the sampling point.

upstream to Grant Falls and downstream to the second rapids (Fig. 26A).

areas where fish moved. This can be done from small moving boats.

**5. Current profiling** 

tagged lake sturgeon

presented and discussed in the text.

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

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

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

Fig. 31. Round Lake ship transect 19 (see 26B).

lake sturgeon habitat but it is only one of several variables.

small waterfalls.

in an Unperturbed Environment: A Small Boreal Lake in the Canadian Shield 393

Interestingly while the larger sturgeon utilized this region they were more offshore. The larger sturgeon were concentrated at the outlet (Fig. 14**)** where currents were 0.25 to 0.5m/sec (Fig. 26B, transects 7, 8 and 9). These currents are below those noted for transect 9 at the inlet to Round Lake. Clearly there is more to the habitat requirements of juvenile lake sturgeon than a certain level of current. It is also apparent that the larger sturgeon frequented areas of the lake where currents were very low (Fig 26B, transect 12) but the ship track suggests a slight amount of counter flow (eddy) in this area. However, there was very little activity by smaller sturgeon in this area of the lake. The larger acoustically tagged lake sturgeon frequently ventured into the river, upstream and downstream from the lake but did not remain in these areas for extended periods of time as they always returned to the lake. None of the tagged lake sturgeon moved out of the area, either due to strong site fidelity or because this region of the Pigeon River is physically isolated due to rapids and

Generally, the smallest lake sturgeon remained in slower flowing water and tended to frequent areas less used by large sturgeon in both deep and shallow regions of the lake. Unlike the larger sturgeon the small sturgeons were rarely located in water under 1 meter. Larger lake sturgeon can move through water with currents as high as 2m/sec but generally frequent areas with currents less than 1m/sec and if situated in the river tend to locate in the back eddies rather than in the main current. Current undoubtedly plays a role in defining

the main flow of the river is becoming apparent and in Fig. 30 there is some evidence for a back eddy on the right side. This back eddy becomes more pronounced in transect 17 (not shown) but declines in transect 18 (Fig. 26B) and the current in both transect 17 and 18 increases to be predominantly 0.7 m/sec. Figure 31 (transect 19) illustrates that the strongest current occurs at the point the river enters the lake and the current across the entire river changes its direction as it passes over rocks on the right side. The majority of the current in Fig. 31 (transect 19**)** and transect 20 is between 0.7 and 1.0 m/sec. Transect 25 below Grant Falls has current ranging from 0.7 to 1.0 m/sec. This was also a region of the Pigeon River where spawning lake sturgeons were found.

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

*Correlation of lake sturgeon movements with current profiles*: The overall frequency of movement of all acoustically tagged lake sturgeon is shown in Fig. 14 and it clearly indicates that activity is concentrated at the inlet and outlets to Round Lake. In the area of the inlet activity is concentrated in the main river channel as it enters the lake. The current at transect 19 (Fig. 26B) is up to 1.0 m/sec but this area is frequented by both large and small sturgeon (Fig. 14). It is worth noting that the current close to the contour of the river bed is < 1.0m/sec so lake sturgeon might be moving through these areas. Figure 14 shows that the smallest sturgeon also concentrated much of their activity in the deepest part of the lake and the main river channel entering the lake (Figs. 9 and 14**)**. By contrast the largest sturgeon spent proportionally less time in the deepest hole in the lake suggesting there may be some segregation of habitat, at the fine scale. It was also noteworthy that the smaller lake sturgeon frequented the area to the left of the outlet from Round Lake, again suggesting that there may be some differences in habitat use between small and large lake sturgeon **(**Fig. 14).

the main flow of the river is becoming apparent and in Fig. 30 there is some evidence for a back eddy on the right side. This back eddy becomes more pronounced in transect 17 (not shown) but declines in transect 18 (Fig. 26B) and the current in both transect 17 and 18 increases to be predominantly 0.7 m/sec. Figure 31 (transect 19) illustrates that the strongest current occurs at the point the river enters the lake and the current across the entire river changes its direction as it passes over rocks on the right side. The majority of the current in Fig. 31 (transect 19**)** and transect 20 is between 0.7 and 1.0 m/sec. Transect 25 below Grant Falls has current ranging from 0.7 to 1.0 m/sec. This was also a region of the Pigeon River

Fig. 29. Pigeon River ship transect 10 Fig. 30. Round Lake ship transect 16

*Correlation of lake sturgeon movements with current profiles*: The overall frequency of movement of all acoustically tagged lake sturgeon is shown in Fig. 14 and it clearly indicates that activity is concentrated at the inlet and outlets to Round Lake. In the area of the inlet activity is concentrated in the main river channel as it enters the lake. The current at transect 19 (Fig. 26B) is up to 1.0 m/sec but this area is frequented by both large and small sturgeon (Fig. 14). It is worth noting that the current close to the contour of the river bed is < 1.0m/sec so lake sturgeon might be moving through these areas. Figure 14 shows that the smallest sturgeon also concentrated much of their activity in the deepest part of the lake and the main river channel entering the lake (Figs. 9 and 14**)**. By contrast the largest sturgeon spent proportionally less time in the deepest hole in the lake suggesting there may be some segregation of habitat, at the fine scale. It was also noteworthy that the smaller lake sturgeon frequented the area to the left of the outlet from Round Lake, again suggesting that there may be some differences in habitat use between small and large lake sturgeon **(**Fig. 14).

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

where spawning lake sturgeons were found.

Fig. 31. Round Lake ship transect 19 (see 26B).

Interestingly while the larger sturgeon utilized this region they were more offshore. The larger sturgeon were concentrated at the outlet (Fig. 14**)** where currents were 0.25 to 0.5m/sec (Fig. 26B, transects 7, 8 and 9). These currents are below those noted for transect 9 at the inlet to Round Lake. Clearly there is more to the habitat requirements of juvenile lake sturgeon than a certain level of current. It is also apparent that the larger sturgeon frequented areas of the lake where currents were very low (Fig 26B, transect 12) but the ship track suggests a slight amount of counter flow (eddy) in this area. However, there was very little activity by smaller sturgeon in this area of the lake. The larger acoustically tagged lake sturgeon frequently ventured into the river, upstream and downstream from the lake but did not remain in these areas for extended periods of time as they always returned to the lake. None of the tagged lake sturgeon moved out of the area, either due to strong site fidelity or because this region of the Pigeon River is physically isolated due to rapids and small waterfalls.

Generally, the smallest lake sturgeon remained in slower flowing water and tended to frequent areas less used by large sturgeon in both deep and shallow regions of the lake. Unlike the larger sturgeon the small sturgeons were rarely located in water under 1 meter. Larger lake sturgeon can move through water with currents as high as 2m/sec but generally frequent areas with currents less than 1m/sec and if situated in the river tend to locate in the back eddies rather than in the main current. Current undoubtedly plays a role in defining lake sturgeon habitat but it is only one of several variables.

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

cannula visible.

Fig. 34. Flushing cannula with syringe to remove air bubbles.

Note occasional negative values.

in an Unperturbed Environment: A Small Boreal Lake in the Canadian Shield 395

 Fig. 32. Initial set up to collect data Fig. 33. Sensor on pectoral fin and cannula from sensor. inserted into the branchial chamber with

Fig. 35. Branchial pressure at 15°C. Fig. 36. Branchial pressure at 22°C.
