Brook lamprey or brown trout soon to be back in our rivers

The chance of us finding brook lamprey or brown trout in our brooks and rivers again in a few years is particularly small. An international study led by KU Leuven shows that we are only taking baby steps with the policy currently in force. More radical measures will be needed for diverse, and therefore healthy, fish stocks.

In 2000, Flanders (as part of Belgium) endorsed the European Water Framework Directive. The horizon was 2015. This deadline passed six year ago, but the objectives are still not being met. An international team of researchers from the KU Leuven, the Flemish Environmental Agency (VMM), the Institute for Nature and Forest Research (INBO), Nord University (No), the Norwegian University of Science and Technology (N) and the University of Helsinki (Fi) investigated how that happened and what needs to be done better.

Doctoral student Io Deflem and Filip Volckaert, professor of Aquatic Ecology and Evolution, at the KU Leuven and their colleagues collected all the data on the water quality and fish stocks in the Flemish waterways. They developed statistical models that take account of the current situation and demonstrate how the fish stocks will respond to the current policy. The result is a sobering one.

“If we meet the current objectives, there will soon be less nitrogen and phosphor in our rivers. That would be a step in the right direction,” says professor Volckaert. “But if we want to fully restore the fish stocks to a decent, enduring condition, we need to set the bar a lot higher.”

A house with the kitchen in the bedroom

“Some species of fish are tolerant. Sticklebacks and carp can survive in difficult conditions too,” says professor Volckaert. “Species like pike, brook lamprey or brown trout find things a lot more tricky.” Inhabitable waterways are about much more than just fresh water. The structure of our brooks and rivers needs to be tackled as well. “The pike needs a flood plain in order to reproduce,” explains professor Volckaert. “The fish lay their eggs in shallow water, where the young animals can develop before trying their luck in deeper waters. There are a few brilliant examples of such restored flood plains in the Scheldt basin, such as the Kruibeke polders. But to really give the animals a chance, there need to be many more of them.”

Our brooks and rivers will also need a different shape. There needs to be more room for tree roots that reach the waterway and thereby bring shade; there needs to be a solution to obstructions such as water mills or locks, and so much more. “At present, our fish are living in a very unnatural habitat,” says professor Volckaert. “It’s as though we were living next to a very busy motorway in a house where the kitchen is in the bedroom. We’d survive, but we wouldn’t really be flourishing.”

The more you measure, the more you know

Data from 2003-2017 was available to the researchers for this study – a truly valuable source of information. “Long-term monitoring is vital,” relates professor Volckaert. “If we want to breathe new life into our fish stocks, we need figures and data to be able to advise on policy, appraise it and adjust it.”

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