UPM’s stream water programme enables the continuation of migratory fish research on the Arvaja rapids

UPM continues its sustainability work on the rapids of the Arvaja watercourse in Jämsä, Finland, by funding research that has been carried out in the area for 40 years. In addition to the upper rapids, a monitoring study has now also been launched at Arvajankoski to assess the impact of the restoration on fish stocks.

A year ago, the old dam of UPM's former paper mill Kaipola in Arvajankoski, Jämsä, was demolished as part of UPM's stream water programme. After the demolition, the rapid was restored, allowing the endangered lake-migrating brown trout to more easily ascend from Lake Päijänne to the Arvaja rapids. There are eight rapids along the approximately 19-kilometre-long route, of which Arvajankoski is the lowest.

Trout have been studied in the Arvaja rapids for a long time. Uninterrupted monitoring started in 1984 and spawning nests have been counted for approximately fifteen years. Funding from UPM's stream water programme now allows the research to continue. "Monitoring is extremely important in order to document the effects of projects such as the restoration of the Arvajankoski rapid," says biologist and fish expert Jukka Syrjänen from the Central Finland Water and Environment Association.

UPM's stream water programme aims to release or restore 500 kilometres of stream waters by 2030. With the restoration of Arvajankoski, a total of almost 60 kilometres of waterways in addition to the Arvaja rapids were freed for trout and other migratory fish, not to mention other stream species.

"The aim of our stream water programme is also to achieve impacts, not just kilometres," says Mikael Rytkönen, Environmental Manager at UPM Energy. "That is why I think it is important that we also contribute to funding research projects like this."

The method used is called electrofishing, where fish are stunned for the duration of the measuring and then released back into the water.

Fingerling density dropped to zero – probably due to fishing

This autumn marked 40 years of continuous annual monitoring of fish in the Kivikoski and Jokelankoski rapids of the Arvaja route. The method used is called electrofishing, where fish are stunned for the duration of the survey and then released back into the water. The main focus has been on monitoring the density of fingerlings, young fish, of the natural trout population along the route.

In the 1980s, the density of 0-yeal-old trout was high, especially in Kivikoski, but in the early 2000’s it started to decline and even reached zero. The other rapids on the route, with the exception of Arvajankoski, had been restored by the ELY Centre of Central Finland in 1996. Water quality on the route remains excellent, and Lake Isojärvi and some intermediate lakes are home to vendace, the best food for lake-migrating fish. The decline of trout was probably due to strong fishing.

In September 2023, the density of 0-year-old trout parr, estimated by catchability, was 38 individuals per acre in Kivikoski and 9 individuals per acre in Jokelankoski. The annual average for the years 2001– 2022 was 25 individuals per acre in Kivikoski and 11 in Jokelankoski, but there was a strong inter-annual variation.

0-year-old trout parrs are measured and released back into the water.

First surveys after restoration carried out at Arvajankoski

The restoration work on Arvajankoski was carried out during the autumn 2022 spawning season, so there were no high expectations of electrofishing results for this year. The electrofishing in October 2023 caught one stocked trout and four European bullheads, which is one of the intermediate hosts of the endangered freshwater pearl mussel and, as a small fish, also a food source for salmonids. A second trout was also sighted but not caught.

"The coming years will show the true state of Arvajankoski. Now there was a lot of water and the conditions for electrofishing were frankly bad," says Tuomo Laitinen, Executive Director of the Central Finland Water and Environment Association. "Also, Arvajankoski renovations were further replenished in mid-August, so this autumn's results can be considered cautiously promising."

Main image: Jukka Syrjänen (left) and Niko Kylliäinen from the Central Finland Water and Environment Association are conducting a study on migratory fish along the Arvaja rapids water course.

UPM’s stream water programme enables the continuation of migratory fish research on the Arvaja rapids

Mikael Rytkönen

Fingerling density dropped to zero – probably due to fishing

First surveys after restoration carried out at Arvajankoski

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