The paper also evaluates the counter’s potential for the monitoring of Finnish fishways.
This report presents the basic principles of the Icelandic “VAKI-Riverwatcher” fish counter and the results of the related reliability tests, conducted in the Merikoski fishway on the River Oulujoki, 2009–2011. The paper also evaluates the counter’s potential for the monitoring of Finnish fishways.
The reliability analysis was performed by validating the VAKI-Riverwatcher fish counter data (fish silhouettes) with underwater video material (reference data) collected simultaneously. The study focused solely on Atlantic salmon and migratory brown trout.
The key questions were:
• How well can salmonids be identifi ed from VAKI-fish silhouettes?
• Can their species and sexes be identifi ed from the VAKI-silhouettes?
• How high is the detection rate of the VAKI-counter for salmon and trout?
During the study period, a total of 1,368 fish were identified (checked from the video data)
as salmon or brown trout passing through the Merikoski fishway. Based on VAKI-silhouettes,
1,193 individuals (87.2% of all observed) could be identified as salmon or trout (although the
particular species could not be confirmed). Bigger fish were easier to identify as salmonids.
Identification of the VAKI-silhouettes of species or sexes was somewhat unreliable. This
problem can, however, be solved by using an underwater camera unit together with the VAKIcounter.
Although camera units are produced by VAKI, underwater camera technology is also
available from several other companies.
The fish detection rate of the VAKI-counter was found to be extremely high (99.7%). From
a randomly chosen video sample (7 days/year, totalling 21 days of data) of 298 salmon and
brown trout, all but one was accurately observed and the data was saved by the VAKI-counter.
Overall, the VAKI-fish counter proved to be an extremely appropriate monitoring method
for Finnish fishways. It is recommended for use in the new fi shway projects under planning,
e.g. in the rivers Kemijoki, Iijoki, Oulujoki and Kymijoki. VAKI-counters are also suitable for
most existing fishways, which are not being monitored at the moment.