Research project on spawning patterns of whitefish in Kokemäenjoki River reaches milestone

A two-month research project focusing on the spawning sites and migratory patterns of the whitefish in the Kokemäenjoki River has reached a significant milestone. At the end of November, hydrophones were removed from the river, which had recorded the acoustic signals from tagged whitefish. The spawning activity for this fall is nearing its end, and receivers placed in the marine area and the lower river will be collected in spring to confirm the fish’s return to the sea.

According to researcher Lari Veneranta, the devices must be retrieved to transfer the accumulated data. Upon accessing the hydrophone, the researcher established a wireless connection to a computer to analyze the raw data. The retrieved data from the current receiver vastly exceeds that from the downstream hydrophones, indicating a prolonged residency of the fish in this area.

This finding aligns with the known fact that the Lammaistenlahti bay is a prime spawning location. Additionally, a dam in Harjavalta restricts fish movements to the upper reaches of the river. From 49 tagged whitefish monitored in Reposaari, 33 ascended the Kokemäenjoki, and 28 reached Lammaistenlahti. Veneranta highlighted that further examination of this data is needed to understand the movements and spawning site locations of these fish.

Kokemäenjoki has faced significant environmental stress, particularly from industrial activity, agriculture, and wastewater over the past century. Original spawning sites have been negatively impacted, but this research will help identify current spawning grounds and evaluate restoration possibilities for whitefish populations. The Kokemäenjoki whitefish population is particularly valuable due to their rapid growth and potential size, with some reaching up to three kilograms.