Double refuge cages were submerged at Lac du Der in order to protect the fish fauna from cormorants. Zoom.
This has become a habit every fall since 2018. The maneuver is quite impressive and meticulous. Early in the morning and in a temperature close to 0°C, sixteen volunteers from the Union of Fishing Federations and Associations for the Protection of the Aquatic Environment (Ufappma) of fishermen from Lake Der, aboard four boats plus a safety one , ensured the immersion of 54 double refuge cages several meters deep with the support of six divers from the Underwater Research and Exploration Group (Gres) of Saint-Dizier.
The refuge cages, 1.25 in diameter by 2.50 m high and made of plastic-coated mesh with a lifespan of twenty years, were fixed one above the other. All were submerged in the South basin, thirty on the side of the Braucourt sailing school and twenty-four along the dividing dike. And this with the aim of offering protection to fish fauna. “The aim is to protect small pike, small zander and small perch aged one or two years. The meshes are large enough to let them pass through“, explains Bernard Mahut, head of the fish management commission of the Ufappma des Pêcheurs du Der.
“More than 300 tons of fish that are eaten”
Who, with a group of volunteers, assembled the shelter cages themselves. In total, they offer 150 m3 of protection against migratory cormorants of which the Lac du Der, at this time, is a privileged passage with the low water level and the absence of vegetation. If a little more than 6,000 cormorants were identified at the beginning of autumn, their number will only increase in the weeks to come. “Cormorants consume on average 425 grams of fish per day, or almost three tonnes per day. Their number will only increase until mid-December, reaching nearly 10,000. More than 300 tons of fish are eaten each fall.“, underlines Bernard Mahut. And the Ufappma des Pêcheurs du Der, chaired by Elie Ribout, has adapted with this shelter cage system over the years. In 2018, there were ten shelter cages on an experimental basis, then 100 of 1m3 in 2019, 150 in 2022, 180 in 2023 and 108 of 3 m3 in 2024. This action has proven its effectiveness since its beginnings through underwater observations carried out by Gres divers both inside and around the refuge cages with the improvement of the fish habitat and their protection against predation from the air.
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