Fisheries Research Services Report No 04/00. H E Forbes, G W Smith, A D F Johnstone and A B Stephen

Transcription

1 Not to be quoted without prior reference to the authors Fisheries Research Services Report No 04/00 AN ASSESSMENT OF THE EFFECTIVENESS OF A BORLAND LIFT FISH PASS IN PERMITTING THE PASSAGE OF ADULT ATLANTIC SALMON (SALMO SALAR L.): YEAR 2 OF A THREE YEAR STUDY H E Forbes, G W Smith, A D F Johnstone and A B Stephen November 2000 Fisheries Research Services Marine Laboratory Victoria Road Aberdeen AB11 9DB

2 AN ASSESSMENT OF THE EFFECTIVENESS OF A BORLAND LIFT FISH PASS IN PERMITTING THE PASSAGE OF ADULT ATLANTIC SALMON (SALMO SALAR L.): YEAR 2 OF A THREE YEAR STUDY H E Forbes 1, G W Smith 2, A D F Johnstone 3 and A B Stephen 4 1 Atlantic Salmon Trust, c/o FRS Marine Laboratory, PO Box 101, Victoria Road, Aberdeen, AB11 9DB 2 FRS Freshwater Laboratory Field Station, Montrose, DD10 8DL 3 FRS Marine Laboratory, PO Box 101, Victoria Road, Aberdeen, AB11 9DB 4 Scottish and Southern Energy, Clunie Power Station, Pitlochry, PH16 5NF SUMMARY This report outlines the results of year two of a three year study. For eight of the 19 weeks between 7 June and 16 October 1999, the numbers of returning adult Atlantic salmon moving into and out of a Borland lift fish pass at Kilmorack Power Station on the River Beauly were recorded. Movements were observed using four CCTV underwater cameras situated outside and within the lower chamber and within and at the exit of the upper chamber. In common with the first year of the study, the aim of the present study was to quantify salmon movements in and out of the lower chamber while the pass was fishing. The results were used to estimate the efficiency of the pass by relating these data to the numbers of fish moving out of the top chamber during the lifting phase. In addition, the present study aimed to examine the movements of fish within the top chamber in relation to the times when fish subsequently exited the pass. In total, 18,895 fish movements into, and 19,164 fish movements out of, the lower chamber were recorded during the 45 day study period. This was less than one third of the movements observed during the 48 day study carried out the previous year. Unlike the previous year s study when the movement of fish in and out of the lower chamber peaked in August, during the present study activity peaked in July. There was no consistent diurnal pattern of movement in and out of the lower chamber within any given month. In common with the 1998 study, only a small proportion of ingoing fish resulted in a net increase in numbers in the lower chamber and residence time within the lower chamber was very short, estimated at between one and two minutes. During the study period, 347 fish were counted moving upstream out of the upper chamber, with numbers peaking in July. As was observed during the 1998 study, fish movement out of the upper chamber exit was greatest between 10 to 20 minutes after the upper chamber filled. Observations of fish in the upper chamber suggested that this delay in the movement of fish out of the pass was a result of the time taken by fish to orientate towards the exit and not due to a delay in fish finding the upper chamber. Averaged over periods of the study for which the numbers of fish in the pass could be estimated, between 91 and 95% of fish available to exit the pass successfully did so. Overall, only a relatively small proportion (between 1.4 and 3.8%) of the times fish entered the lower chamber during the fishing phase did this result in a fish ascending and exiting the pass upstream during the subsequent lifting phase. 1

3 An Assessment of the Effectiveness of a Borland Lift Fish Pass INTRODUCTION In May 1998, a three-year project was initiated to study the movement of fish through a Borland lift fish pass located in Kilmorack Power Station, Inverness-shire. The study aims to build on observations made during two smaller studies carried out at the same site in 1995 (Smith et al., 1996) and 1996 (Smith et al., 1997) and identify where changes can be made to the operation of the fish pass which will improve efficiency. Results from the first year of this three-year study indicated that movement in and out of the lower chamber varied between months, peaking in August (Forbes et al., 1999). Only a small proportion of the fish entering the lower chamber resulted in a net increase and residence time within the lower chamber was very short, at between one and two minutes. It was estimated that up to 721 fish were to be found in the lower chamber during the study period, but even at the highest density estimated, there was no evidence that increasing numbers of fish in the lower chamber inhibited further movement into the pass. Unlike movement into the lower chamber, the largest number of fish exited the pass during July, with fish exiting the upper chamber in the greatest numbers between 15 to 20 minutes after the upper chamber filled. Of those fish which were retained within the pass during a lift, it was estimated that 82% successfully exited the top chamber. This report outlines the results of the second year of study and compares the data with the findings from previous studies. The data will also be used for analysis to suggest changes to the operation of the pass. The effectiveness of operational changes in improving pass efficiency will be tested in year 3 of the study. The Study Site MATERIALS AND METHODS Kilmorack Power Station and dam are situated on the River Beauly, approximately 5 km upstream of the river mouth (Fig. 1). The Borland lift fish pass comprises a basic design of a lower chamber located at the tailrace of the dam, connected by a shaft to an upper chamber located 18 m above at the surface of an impounded reservoir (Fig. 2). Water flow through the pass is controlled by electrically-operated gates fitted at the entrance to the lower chamber and at the exit of the upper chamber. When the lower chamber is open, referred to as the fishing phase, fish migrating upstream are free to move in and out of the lower chamber. At set periods each day the gate of the lower chamber closes, the lift fills up with water and fish held in the lower chamber are free to swim to the upper chamber, exit and continue their upstream migration. Such periods are referred to as the lifting phase. At Kilmorack three lifting phases take place every 24 hours, the lower gate beginning to close at 0800, 1230 and 1800 hours (BST). Each lift lasts approximately two hours, during 75 minutes of which the pass is full of water and fish are free to exit. No lifts take place during darkness. Equipment Setup Four CCTV cameras (System Q, CCT855, Aqua cameras) contained within purpose-built stainless steel mounts were employed to observe fish movement at various locations within the pass. Three of these cameras were deployed in the same positions as in the first year of the study (Forbes et al., 1999a) and provided footage of fish entering and exiting the lower chamber and fish exiting the top chamber (Fig. 2). In addition, for the current study, another camera was positioned in the upper chamber, facing upwards towards the exit of the pass 2

4 An Assessment of the Effectiveness of a Borland Lift Fish Pass (Fig. 2, camera 4). Although showing an unknown proportion of the number of fish in the upper chamber the camera was used to provide an index of fish numbers at any given time during the lifting phase. A full description of the recording equipment set-up is given in Forbes et al. (1999). A schematic representation of the equipment setup is presented in Figure 3. Data Handling Video tape recordings of fish movement commenced on 7 June 1999 and recordings were made for eight of the 19 weeks to 16 October No artificial illumination was used in the lower chamber and observations were restricted to the period 0600 to 2100 hours (BST). During tape play-back analysis, fish movement was recorded as the numbers of fish entering and exiting the lower chamber during each minute of the fishing phases, and the numbers of fish exiting the upper chamber during each minute of the lifting phases. An index of the numbers of fish present in the upper chamber was derived from camera 4 (Fig. 2) by counting the number of fish in a single frame at the beginning of each minute for three of the weeks between the 5 July 1999 and 7 August Fishing phases were identified as between lifts 1 and 2 (fishing phase a) and between lifts 2 and 3 (fishing phase b). Rainfall Data Daily rainfall data were obtained from Scottish and Southern Energy for a site 1 km upstream of Kilmorack. Other environmental parameters, namely water turbidity, surface water temperature, water flow and atmospheric pressure, were collected during the first year of the study (Forbes et al., 1999), but could not be shown to influence the movement of fish through the pass. Consequently, these parameters were not recorded during the current study. Rainfall Data RESULTS AND DISCUSSION Mean daily rainfall during each month of the study period is presented in Figure 4. For reference, comparative figures averaged over the period and over the study period in 1998 are also given. In 1999, the greatest rainfall levels were experienced during the two weeks of observations in July, while the one week of study during October experienced the lowest levels of rainfall. Run Size Figure 5 shows the number of fish registered by the counter at Kilmorack during each month of 1998 and During 1998, the total number of fish ascending the pass was 5,272 while during 1999, the comparable figure was only 1,260 (24% of the 1998 figure). Consequently, the analysis for 1999 was based upon far fewer fish than were available in previous studies. The lack of fish placed several limitations on the analysis conducted and will be discussed in greater detail in subsequent sections. 3

5 An Assessment of the Effectiveness of a Borland Lift Fish Pass Movement of Fish in Relation to the Lower Chamber a) Movement In and Out of the Lower Chamber Up to 56 adult salmon per minute were recorded moving into the lower chamber while a maximum of 38 fish per minute was recorded out during the 45 days of the study. This compares with the 1998 study when up to 100 fish per minute moved into, and 85 fish per minute moved out of, the lower chamber over 48 days (Forbes et al., 1999). Movement in and out of the lower chamber varied significantly with month during the present study (Fig. 6a: Kruskal-Wallis one-way analysis of variance; Counts in, N=515, H=77.46, P<0.001; Counts out, N=515, H=75.73, P<0.001), with peak activity occurring in July. The net count also varied significantly with month (Fig. 6b: Kruskal-Wallis one-way analysis of variance; N=515, H=18.56, P=0.001). In common with the observations in 1998 (Forbes et al., 1999), there was no consistent diurnal pattern of movement in and out of the lower chamber within any given month. b) The Proportion of Fish Retained in the Lower Chamber As in previous studies (Smith et al., 1997; Forbes et al., 1999), considerable activity was observed at the entrance to the lower chamber. In total, 18,895 fish counts into, and 19,164 fish counts out of, the lower chamber were recorded, giving a net count of -269 fish entering the pass (a retention rate of -1.4% of the total counted in). This compares with the 1998 study, when a total of 67,509 fish was recorded entering the lower chamber and 63,894 were recorded moving out over 48 days (Forbes et al., 1999). As reported in the 1998 report (Forbes et al., 1999), there exists a bias towards the counting of fish out of the lower chamber. The effect of this bias, coupled with the extremely low runs of fish encountered during this year of study, is to produce negative net counts, producing the false impression that there are more fish exiting the pass than entering it. However, although the interpretation of absolute numbers may prove misleading, analyses of the general trends in fish counts over time may still prove instructive. Retention rate varied significantly between months of the study (Kruskal-Wallis one-way analysis of variance; N=80, H=23.09, P<0.001), with September and October experiencing the lowest retention rates. During the 1998 study, the lowest retention rate also occurred during September, but increased during October when there was considerably more rainfall than was experienced for the same month during this year of the study (Forbes et al., 1999). No statistically significant difference between retention rates in the morning (phase a) and the afternoon (phase b) existed during any of the months of the study. c) Mean Residence Time in the Lower Chamber Unlike radio tracking studies where the residence time of individual fish in the lower chamber can be studied directly (Smith et al., 1997), the current population-based study requires more indirect methods of analysis to provide the same information. For each fishing phase, auto-correlation analysis was carried out on the time series of net counts into the lower chamber to test whether any relationship existed between net counts into the chamber and net counts at a point some time later (Fig. 7). Of the 67 fishing phases analysed, 46 showed a significant negative correlation (P<0.05) when lagged by one minute, 21 were significant when lagged at two minutes, eight were significant when lagged at three minutes and for all other lag periods between four and 30 minutes, the number of significant negative correlations did not exceed six in each case. This pattern was consistent between months and times of the day. 4

6 An Assessment of the Effectiveness of a Borland Lift Fish Pass Thus net counts of fish entering the lower chamber tended to be followed by net counts out of the chamber up to three minutes later, which may be interpreted as indicating that average residence time in the lower chamber was very short. These findings are consistent with data from both the radio tracking study (Smith et al., 1996), the pilot study (Smith et al., 1997) and the 1998 study (Forbes et al., 1999). The considerable fish activity into and out of the lower chamber, together with low residence times in the lower chamber, suggest that pass performance may be improved if the retention time of fish in the lower chamber is increased. Although several factors may affect the behaviour of fish in the lower chamber, water flow has been shown to provide an essential stimulus to attract fish into the lower chamber (Smith et al., 1996). Analysis of the relationship between flow through the fish pass and the subsequent numbers of fish ascending the pass will be examined in the third year of the study. d) Movements of Fish Out of the Lower Chamber Immediately After Fish Lifts Movement of fish out of the lower chamber after lifts was comparable with that observed in the 1998 study (Forbes et al., 1999). At the beginning of each fishing phase, following the opening of the lower gate, there was a general net movement of fish out of the lower chamber (Fig. 8). The net movement out continued until flow through the lower gate recommenced, 14 minutes after the lower gate began to open. The initial net movement out of the lower chamber following the lifting phase confirms that not all fish present in the pass during each lift successfully exited the pass. This observation was used to derive a minimum estimate of the number of fish remaining in the fish pass which in turn was used to provide a minimum estimate of the efficiency of the lifting phase (Smith et al., 1997). These analyses will be developed further in the following sections. Movements In and Out of the Upper Chamber a) The Number of Fish in the Upper Chamber During both the 1998 study (Forbes et al., 1999) and the pilot study in 1996 (Smith et al., 1997) it was observed that fish did not begin to exit the upper chamber in large numbers until minutes after the pass had filled. It was not clear during either study, however, whether this delay was a result of fish remaining in the lower chamber or a result of fish delaying their exit from the top chamber. In an attempt to address this question, a camera was placed in the upper chamber and from it an index of fish in the upper chamber was derived for 39 of the 118 lifts recorded during the study period. The index was obtained by counting the number of fish in a single frame at the beginning of each minute for the duration of each lift. The index of fish numbers in the upper chamber was significantly non random with respect to time during the lifting phase (Fig. 9: Kruskal-Wallis one-way analysis of variance; N=39, H=131.04, P<0.001). The count was highest at the beginning of the lift, steadily decreasing to a minimum at the end of the lift. The large number of fish observed in the top chamber immediately after the pass filled suggests that there was no delay in fish reaching the top chamber and that any delay in these fish exiting the pass must be attributed to fish remaining in the top chamber. The implications of this will be discussed further in a subsequent section. 5

7 An Assessment of the Effectiveness of a Borland Lift Fish Pass b) The Numbers of Fish Exiting the Upper Chamber A total of 347 fish was observed exiting the pass during the present study, considerably less than the 1,954 fish observed during the previous year s study (Forbes et al., 1999). There was a significant relationship between month and the numbers of fish exiting the upper chamber (Fig. 10: Kruskal-Wallis one-way analysis of variance; N=118, H=28.31, P<0.001), with numbers peaking in July and dropping to a minimum in October. This reflected the movement of fish in and out of the lower chamber which also peaked in July and fell to a minimum in October (Fig. 6a). During the 1998 study (Forbes et al., 1999), the numbers of fish exiting the pass also peaked in July and dropped to a minimum in October, although activity around the lower chamber peaked during August. It appears, therefore, that maximum fish movement out of the top chamber, does not always coincide with maximum movement into and out of the lower chamber. Results from both the 1998 study (Forbes et al., 1999) and the current study (Kruskal-Wallis one-way analysis of variance; N=118, H=1.61, P=0.448) suggest that there is no clear pattern in the movement of fish out of the pass and time of day. For each fishing phase, the numbers of fish exiting the fish pass were aggregated over consecutive five minute periods. At the beginning of a lifting phase, 15 minutes elapsed before the water level reached the top gate, after which time fish were free to exit the upper chamber for a period of 75 minutes, before water levels fell again. The movement of fish out of the upper chamber was significantly non random with respect to time during the lifting phase (Fig. 11: Kruskal-Wallis one-way analysis of variance; N=1755, H=154.68, P<0.001). Counts were lowest during the first five minutes (15 to 20 minutes after the lower gate closed) and the last 40 minutes (50 to 90 minutes after the lower gate closed), with a peak in numbers exiting between 10 to 20 minutes (25 to 35 minutes after the lower gate closed). These observations are similar to those made during the 1998 study, when the number of fish exiting the top chamber peaked between 15 to 20 minutes (30 to 35 minutes after the lower gate closed) (Forbes et al., 1999). As outlined earlier, analysis of the number of fish in the top chamber during a lift, suggested that the delay in fish exiting the top chamber was a result of a delay in fish orientating towards the exit. If the location of the exit were more readily apparent to fish, this delay in finding the exit may be reduced and as a consequence a greater proportion of fish may exit the pass during the first hour of each lifting phase. One potential method to more clearly identify the fish pass exit would be to reduce light level in the upper chamber, leaving only the exit over the counter flume to transmit ambient light into the upper chamber. In such an environment the fish may orientate towards, locate and pass through the exit more quickly. The benefits of reducing light level in the top chamber will be examined during the third year of the study. During the 1998 study (Forbes et al., 1999) the effect of changing the length and number of lifting phases was assessed using a predictive model based on data collected during that year. Assuming that the reduction in the overall length of fishing phases resulted in no reduction in the numbers of fish available to be lifted, then the model predicts that reducing the length of each lifting phase by 30 minutes and increasing the number of lifting phases to four, would result in approximately a 13% increase in the number of fish exiting the pass each day. In order to test the predictions of this model, it was decided to operate an additional lift during the third year of the study and examine the effect on the numbers of fish subsequently exiting the pass. Traditionally, the fish pass at Kilmorack has not lifted fish during the hours of darkness. Therefore, the inclusion of a night time lift will also be 6

8 An Assessment of the Effectiveness of a Borland Lift Fish Pass examined to establish whether it significantly increases the numbers of fish lifted by the pass. c) The Proportion of Fish Exiting the Upper Chamber To calculate lifting phase efficiency, the lifts during which no fish ascended the pass were excluded from the analysis. Additionally, as with the previous study, lifts were excluded when the minimum count in the following fishing phase occurred after water began flowing through the pass. Due to the low numbers of fish ascending the pass during this year of the study, suitable data were obtained for only 23 of the available 118 lifts, during which a minimum estimate of 159 fish were available to ascend the pass. Of these, 144 (90.6%) successfully negotiated the pass, a figure similar to that experienced in the 1998 study (82%) (Forbes et al., 1999). There was no significant association between the proportion of fish successfully ascending the pass and the time of day at which the lift operated (Kruskal- Wallis one-way analysis of variance; N=23, H=1.27, P=0.53). Month also had no significant effect on the proportion of fish counted out of the pass (Fig. 12: Kruskal-Wallis one-way analysis of variance; N=23, H=0.00, P=0.998). No suitable data was available for September and October and therefore no conclusion could be drawn regarding pass efficiency during these months. However, because it is only possible to estimate the minimum number of fish in the pass during a lifting phase, a figure of 90.6% is a maximum estimate of the efficiency of the lifting phase. In addition, during the pilot study (Smith et al., 1997) it was estimated that only 40% of fish present during a lift successfully negotiated the pass. It was, therefore, decided to adopt a second method of estimating the minimum number of fish in the pass using the observations of fish in the upper chamber. For each of the 39 lifts for which counts of fish in the upper chamber were obtained, the number of fish in a frame at the beginning of each minute of a lift was added to the number of fish which had exited the pass up to that point in time. The maximum figure obtained for each lift provided a minimum estimate of the number of fish available to exit the pass. Using this method, it was calculated that a minimum estimate of 233 fish were available to ascend the pass. Of these, 222 (95.3%) successfully negotiated the pass (90.6% using original method). Therefore, although the two methods give a maximum estimate of lifting phase efficiency, both independent estimates are similar, at between 90 and 95%. d) Overall Pass Efficiency During the current study, only 1.8% of the fish counted entering the lower chamber, exited the top chamber. This compares with 3.8% during the pilot study (Smith et al., 1997) and 2.9% during the 1998 study (Forbes et al., 1999). During the radio tracking study, when only the movement of individual fish which subsequently exited the pass was recorded, only 1.4% of the occasions when fish entered the lower chamber resulted in fish exiting the upper chamber (Smith et al., 1996). It appears, therefore, that individual fish make a large number of visits to the lower chamber, before eventually successfully negotiating the lift and that this behaviour is true for the majority of fish using the pass and not a consequence of just a few fish persistently entering and exiting the pass with no motivation to ascend upstream. In addition, this behaviour takes place, irrespective of the magnitude of the run of fish at any given time, as is clear from comparing data between 1998 (Forbes et al., 1999) and

9 An Assessment of the Effectiveness of a Borland Lift Fish Pass CONCLUSIONS Observations from the current study together with previous data (Smith et al., 1996; Smith et al., 1997; Forbes et al., 1999) provide a consistent general picture of salmon movements through the Borland lift fish pass at Kilmorack dam. Χ Χ Χ Χ Χ Despite consistently large numbers of fish counts into and out of the lower chamber, only a small proportion of these counts resulted in a net increase of fish in the pass. Residence time in the lower chamber was very short, at between one and two minutes. There was no evidence that, up to the maximum cumulative fish count observed in the lower chamber (721), increasing numbers of fish in the lower chamber inhibited further movement into the pass. Fish movement out of the upper chamber peaked between 10 to 20 minutes after the upper chamber filled. Data from the present year s study suggest that this delay in the movement of fish out of the pass is a result of the time taken by fish to orientate towards the exit and not due to a delay in fish finding the upper chamber. Observations of fish movement out of the lower chamber following lifting phases was evidence that not all fish exited the pass when lifting. However, data from 1998 and the current year of study, suggests that up to between 82 and 95% of fish present in the lower chamber when the gate closes, may successfully negotiate the pass. $ Overall, between 1.4 and 3.8% of the times fish entered the lower chamber during fishing phases did this result in fish ascending and exiting the fish pass during the subsequent lifting phase. PROPOSALS TO MODIFY THE OPERATION OF THE BORLAND LIFT DURING THE THIRD YEAR OF STUDY As noted elsewhere in the text, during the third year of the study the intention is to make four modifications to the operation of the pass. For ease of reference, these are listed below: 1. evaluate the effect of changing the flow of water through the pass during fishing phases on the number of fish exiting the pass during the subsequent lifting phases; 2. evaluate the effect of changing the number of day time lifts on the total daily numbers of fish ascending the pass; 3. evaluate the effect of adding a night time lift on the total daily numbers of fish ascending the pass; 4. evaluate the effect of reducing light intensity in the top chamber, leaving only ambient light at the exit visible to fish in the pass, on the time taken by fish to exit the upper chamber during the lifting phase. 8

10 An Assessment of the Effectiveness of a Borland Lift Fish Pass ACKNOWLEDGEMENTS We are grateful to The Atlantic Salmon Trust for their cooperation and to the Beauly District Salmon Fishery Board who provided financial assistance and support throughout. Thanks are also extended to Sandy Thow and Dave Kendrick of Scottish and Southern Energy for their invaluable help throughout the study and to Gail Foster who assisted with some of the field work. Dick Shelton, Tony Hawkins and Campbell McDonald commented on an earlier draft of this report. The illustrations of the site location and dam were provided by Keith Mutch and Alvan Rice and the Typists at the Marine Laboratory produced the final typescript. REFERENCES Forbes, H.E., Smith, G.W., Johnstone, A.D.F. and Stephen, A.B An assessment of the effectiveness of a Borland lift fish pass in permitting the passage of adult Atlantic salmon (Salmo salar L.). Fisheries Research Services Report, 10/99, 13pp. Smith, G.W., Johnstone, A.D.F and Shearer, W.M The behaviour of returning adult Atlantic salmon (Salmo salar L.) at a Borland lift fish pass as determined by radio telemetry. Fisheries Research Services Report, 7/96, 12pp. Smith, G.W., Johnstone, A.D.F., Shearer, W.M. and Carter, T.J The behaviour of adult Atlantic salmon (Salmo salar L.) in a Borland lift fish pass as determined by underwater television observations. Fisheries Research Services Report, 10/97, 22pp. 9

11

12

13

14

15

16

17

18

19

20

21

22