Trout and sea trout populations studied in the Ciecere River
Researchers from the BIOR scientific institute presented a study of fish populations in the Ciecere River at Saldus library. Juvenile numbers have grown, but larger fish are fewer and ecological quality is rated low.
On 21 October 2026, the Saldus municipality library hosted the presentation of a study on changes in brown trout and sea trout populations in the Ciecere River, above and below the Pakuļi reservoir in western Latvia. The study was carried out by researchers of the scientific institute BIOR, who compared the results with 2018 data. The findings matter for the river's future management because they show that the state of the fish depends on several factors.
What the researchers found
The results were presented by Kaspars Abersons, a researcher in BIOR's Fish Resources Research Department. Fish were counted by electrofishing at 12 sites across three river sections, mostly revisiting places surveyed in 2018. The team also assessed the river's physical-chemical and hydromorphological parameters and carried out a fish parasitological study.
In total, 19 fish species were recorded. Compared with 2018, the number of juvenile brown trout rose, while the number of larger trout fell in almost all surveyed sites. The fish index value dropped at nearly all revisited sites: in the upper and middle reaches it corresponds to very low ecological quality, and in the lower reaches to low or moderate quality. The share of rapids has also declined, especially in the upper reaches.
The researchers stress that the changes cannot be explained by a single cause. Habitat quality, water flow regime and fish's ability to move along the river all need attention.
Recommendations
The researchers advise reducing the impact of hydropower plants and dams, ensuring conditions for fish migration and adequate ecological flow. They also suggest improving habitats by increasing the share of pebbles and gravel on the riverbed, which is needed for spawning and egg development. In some sections, artificial breeding and stocking of brown trout could be considered, while poaching should be limited and measures to reduce angling pressure assessed.
The study notes that earlier trout stocking above the Dzirnavnieki hydropower plant did not lead to an established population.
Lecture on sea trout
In the second part of the event, Jānis Bajinskis, a BIOR researcher and Latvia's representative in the ICES working group on Baltic salmon and sea trout stock assessment, spoke about the state of sea trout and the management of sea trout rivers in Latvia. He explained the fish's biology, life cycle and threats: habitat area and quality, migration barriers, hydrological regime, climate and food availability. Preserving habitats requires free migration routes, suitable spawning sites, retained riverbank vegetation and regular monitoring, along with attention to the effects of climate change.
