New technique tracks whitefish movements in Kokemäenjoki River and Pori, Finland

A new technique is providing precise data on the movements of whitefish in the Kokemäenjoki River and the marine areas off Pori, located in Satakunta. Understanding the pathways and spawning sites of whitefish is expected to contribute to the sustainability of their population in the Kokemäenjoki.

Researchers from the Natural Resources Institute Finland (Luke) marked 24 fish in the initial phase, each fitted with a small transmitter inserted into their abdominal cavity. “The acoustic tag is a small capsule that emits sound,” explained researcher Lari Veneranta. The sound frequency of the transmitter is so high that it is inaudible to humans.

To attach the transmitter, the fish is first placed into a box containing anesthetic. Once it becomes unconscious, a small incision is made in its abdomen to insert the transmitter, which requires careful handling due to the many membranes present in the fish. Afterward, the incision is stitched closed, and the fish is released back into the water.

Veneranta expressed hope that if recreational fishermen catch a whitefish with a transmitter, they should consider releasing it back into the water if it is in good condition. In cases where the fish is dead or in poor health, the tag can be returned free of charge to Luke.

This project marks the first time whitefish are being tagged, with previous studies focusing on other fish species such as salmon and trout. The gathered data on whitefish behavior and spawning sites will aid in managing fish populations effectively.

The tagging effort is part of a broader initiative funded by the annual fisheries fees collected from hydropower plants along the Kokemäenjoki, aimed at mitigating the ecological repercussions caused by dam construction. The marking process will continue next week in Reposaari, Pori.