Video monitoring of salmon and trout passage
at the Neiden fish ladder in 2009
Working report
4.3.2010
Panu Orell
Finnish Game and Fisheries Research Institute
River Tenojoki Fisheries Research Station
1. Introduction
The River Neiden (Näätämöjoki in Finnish, drainage area 2962 km2) is one of the most important salmon rivers in both Norway and Finland with annual in-river catches varying between 3 and 16 tonnes (1972-2009 mean catch 8.5 t). Most of the salmon production area is located in Finland, but the river is flowing the lowermost 30 km in Norwegian side. At the Norwegian side there is a strong waterfall, Skoltefossen, located c. 10 km upstream from the sea. Based on bilateral agreement (in 1951) between Finland and Norway a fish ladder has been built to Skoltefossen waterfall (in 1968) to enhance the passage of salmon and trout.
The efficacy of the Skoltefossen fish ladder has been occasionally studied by using underwater video monitoring techniques. The most recent efficacy studies have been conducted during 2002-2003 and in 2006. The monitoring of the Skoltefossen fish ladder was repeated in 2009 by Finnish Game and Fisheries Research Institute (FGFRI) in co-operation with Fylkesmannen i Finnmark. The funding of the Neiden video monitoring was arranged by Fylkesmannen i Finnmark. FGFRI provided the video equipment.
This working report presents the result from the video monitoring of salmon and trout passage at the Neiden fish ladder in 2009 in relation to the earlier results.
2. Methods
One underwater camera (Camera: Watec, WAT-902 H, housing: custom made by Lamberg Bio-Marin) with a 3.5 mm wide angle lens was installed above the last pool of the fish ladder (see the opening page photo). The camera was placed on left hand side of the fish ladder (looking from the downstream) and the camera view covered totally the area where fish had to swim when passing the fish ladder and ascending to the natural river channel. The data was recorded to 500 GB hard disks by using SANYO DSR-300 digital video recorder. The data was saved at enhanced quality with a recording rate of 2.72 fields/second. Artificial illumination (underwater halogen light) was used at the video monitoring site after 8th of August to be able to record data during the nights (Fig. 1).
Figure 1. The installation of underwater camera (right) and underwater halogen light (left) at the video monitoring site in the River Neiden in 2009.
The video monitoring was started at 15th June, right after the environmental conditions (river flow) were good enough for the camera installation. Monitoring was continued until the end of August. The time window covered efficiently the salmon migration period and the most important part of the trout migration.
The collected data was analysed during autumn-winter 2009-2010 by experienced staff at the River Tenojoki Fisheries Research station in Utsjoki (FGFRI). Observed salmon were classified to three different size categories including 1SW (one-sea winter, salmon <65 cm), 2SW (two sea-winter, salmon 65-90 cm) and MSW (multi-sea winter, salmon >90 cm). Sea trout included all trout that were estimated to be > 30 cm long. The size estimation of fish was based on subjective decisions by the data-analyser and therefore they may not be fully accurate in all cases.
3. Results
3.1. Salmon
In 2009 the salmon migration in Skoltefossen fish ladder activated at late June. A short depression in migration activity was evident at the first week of July where after the migration activated significantly and reached the peak at 13th July (Fig. 2). The migration activity started to decrease after 24th of July and during later half of August only few fish ascended the fish ladder daily (Fig. 2).
Most of the salmon (86 %) that passed the fish ladder were one-sea-winter salmon (1SW). The proportion of 2SW and MSW salmon were 12 % and 2 % respectively (Table I). The migration of 2SW and MSW salmon was significantly more active in the first half of the monitoring period compared to the latter half (Table I, Fig. 2).
Table I. Numbers and percentages (%) of 1SW, 2SW and MSW salmon observed passing the Skoltefossen fish ladder during three different time periods in 2009.
The number of salmon passing the Skoltefossen fish ladder was significantly lower in 2009 when compared to the numbers counted in 2006 (Fig. 3, Table II ). In 2006 a significant peak in migration activity of salmon was observed in the first half of August, which was not observed in 2009 (Fig. 3). The migration activity was, however, very low in the latter half of August in both years (Fig. 3). The numbers of salmon passing the fish ladder in 2002-2003 were slightly lower than in 2009 (Table II).
Figure 2. Numbers of 1SW, 2SW and MSW salmon ascending the Skoltefossen fish ladder between 15th June and 31st August 2009.
Figure 3. Numbers of salmon ascending the Skoltefossen fish ladder in 2006 and 2009. In 2006 the monitoring period was 7th June-31st August, and 15th June- 31st August in 2009.
Table II. The numbers of 1SW, 2SW, MSW, undefined salmon (sea-age not determined) and sea trout passing the Skoltefossen fish ladder in 2002-2003, 2006 and 2009 and the periods when the video monitoring was conducted. In 2002-2003 the monitoring period includes some days when the video system was not operating. Data from 2002-2003 is provided by Lamberg Bio-Marin.
3.2. Sea trout
The sea trout migration in the fish ladder in 2009 activated at end of July and the migration was rather active to the end of the monitoring period (Fig. 4). The migration timing pattern was very similar when compared to the pattern observed in 2006 (Fig. 4).
In total, over 500 sea trout passed the fish ladder during the monitoring period in 2009 (Table II). This was slightly more than in 2006 and clearly more than in 2002-2003 (Table II). The observed sea trout numbers are minimum estimates as the migration period of trout extends to September which was not monitored during the study years.
In addition to salmon and sea trout 18 pink salmon (Oncorhynchus gorbuscha) individuals were observed passing the fish ladder in 2009. These fish passed the fish ladder during late-July and mid-August.
Figure 4. Numbers of sea trout (trout > 30 cm in length) ascending the Skoltefossen fish ladder in 2006 and 2009.
4. Conclusions
Salmon used the Skoltefossen fish ladder throughout the monitoring period in 2009, although the active migration window lasted only one month, from early July to early August. Compared to the migration timing of salmon at the River Teno system, the salmon ascended the Skoltefossen fish ladder rather late in the season. For example in the River Utsjoki, a tributary of Teno, (located 106 km upstream from the River Teno mouth), the active salmon migration period is annually between mid-June and Mid-July. The late passage of salmon at the fish ladder in Neiden may indicate that the waterfall hinder the upstream migration of salmon. Alternatively, it is possible that the fish enter the Neiden system significantly later compared to the River Teno system. If salmon are stopped for some time below the Skoltefossen area the fish may suffer rather high fisheries exploitation as the area is intensively fished with rod and line and with the cast seine (Käpälä).
In total c. 2000 salmon passed trough the Skoltefossen fish ladder in 2009. The passage activity was significantly larger in 2006. The year 2006 was, however, significantly better salmon year in Neiden, which is clearly demonstrated by the salmon catches. The catch of the Neiden system was 13.0 tons (c. 3800 individuals) in 2006 whereas it was only 7.4 tons (c. 2000 individuals) in 2009. The numbers of salmon ascending the fish ladder in 2002-2003 were in line with the numbers observed in 2009. Its seems that the year 2009 was only an average salmon year in Neiden, demonstrated both by the total catch and the number of salmon observed passing the fish ladder.
In addition to salmon, over 500 sea trout was observed to pass the fish ladder in 2009. The number of sea trout in 2009 was the largest during the monitoring period 2002-2009. The total number of sea trout is actually even larger as the migration window of trout continues to September, when video monitoring is not normally conducted. Thus, the sea trout population in the river Neiden seems to be rather strong. The migration of trout is concentrated to August and the exploitation rate on trout may be significantly lower compared to salmon as the fishing effort is usually decreasing in late-summer period.
All in all, the Skoltefossen fish ladder is a working fish pass and both salmon and sea trout use it actively from year to year. Unfortunately no reliable reference information is available about the numbers of fish ascending straight from the waterfall. This kind of data would allow estimating the proportion of fish using the fish ladder and the total number of salmon ascending upstream from the Skoltefossen on annual basis. Based on long-term scale sampling data from the Käpälä- fisheries it, however, seems that the fish trying to ascend straight from the waterfall are generally larger than fish that use the fish ladder (FGFRI/NINA, unpublished data).
Underwater video monitoring of the Skoltefossen fish ladder has proved to be effective monitoring approach. By utilizing video monitoring on annual basis a good index of the status of salmon (and sea trout) populations of the River Neiden could be obtained also in the future. This kind of long-term monitoring is needed to make estimates about the annual variations and long-term trends of salmon stocks in the River Neiden. To estimate the total abundance of salmon passing the Skoltefossen it could be possible to use underwater video monitoring just above Skoltefossen on the south side of the river, where the salmon are supposed to overcome the waterfall.
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