A spearfish with a transmitter in its belly swam at least 550 kilometers up the Rhine in five years. This is astonishing for a species of fish that was always thought of as a resident fish, and which remains in the same habitat all year round.
The fish swam upstream all the way from the North Sea to Mannheim in Germany. “This really surprised us,” said researcher Nils Breve of Wageningen University and Research when asked. “The entire fisheries management may need to be adjusted.”
The perch in question was caught on February 26, 2017 in Haringvliet during National Fishing Day, according to nature today, where biologists, nature organizations, and research institutions share their news. The goal was to see if freshwater fish entering the North Sea from the river were doomed, or if they could survive the sea temporarily and swim back into the river.
To test this, seventy walleyes were caught, fitted with a transmitter and launched into the brackish water on the seaward side of the Haringvliet manholes. The research, published in 2018, showed that some of the eyes were actually able to find fresh water from Haringvliet. The fish in question were part of this study.
“It’s very strange, if you think for years that you have completed a study correctly, then after five years you find that it is continuing,” says Niels Privé of Wageningen University and Nature Research Today. Recently, Beekebirch 11328 was caught in the port of Mannheim by a professional fisherman. Spoiler alert: The fish didn’t survive that. It is prepared, served and eaten.” The fisherman sent the fish transmitter to Wageningen.
A spear perch can swim 1.5 meters per second. “But that’s his running speed,” Privé says over the phone. “I know they can swim fast, but they usually don’t. At Haringvliet they have everything they need.” This is what makes this discovery so surprising. The consequences can be significant. “Each country on the Rhine still has its own fisheries department, but that may now need to be adjusted,” says Privet. “Maybe it should be like sea fishing, joint management.” In short, pike perch 11328 has a swam history.
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