‘Sludge! No shot!’ it almost sounds like an off-the-cuff joke, but it’s serious science. Anyone walking along the Gastersche Diepje during the research by the Hunze en Aa’s Water Board will regularly hear the researchers shouting.
They are busy with the annual research into the river lamprey, a special species that still occurs here.
Every year a section of approximately 250 meters of the Diepje is sampled. A piece of the stream bed is lifted up with a metal grab of about ten kilos. “We carefully sieve everything we bring up,” says Peter Paul Schollema of the Hunze en Aa’s water board. “We look at what lives in the bottom and what kind of material is present. When we find river lampreys, we measure them and determine their age. This gives us a good idea of the spawning grounds and how the river lamprey develops here.”
In addition to the annual survey, a larger section of approximately 7.5 kilometers is sampled once every three years.
It is special that the river lamprey manages to find its way to the Gastersche Diep. It is the only place in the Northern Netherlands where this species still spawns. “For the nearest other populations you have to go to the Veluwe, the Achterhoek or even all the way to Limburg,” says Schollema. “That makes it extra special that the species still occurs here.”
The river lamprey follows an impressive route: via the Drentsche Aa it swims through the city of Groningen and the Eemskanaal towards Delfzijl, eventually ending up in the Wadden Sea. Every year the animals return from the sea to Gasteren to spawn there.