Biodiversity conservation and fish production in ponds: a contradiction?
Résumé
The Dombes region is an important French “pondscape”, and a major landscape with extensive fish farming ponds in Western Europe. These ponds are originally man-made, established by monastic communities in the Middle Ages, and used to extensive fish production for centuries. Although this anthropogenic origin, they are also highly recognised for their strong contribution to regional biodiversity. A profound understanding of how management affect biodiversity patterns is crucial for effective long-term conservation. We have analysed the effects of fish farming management practices on the species richness and cover of aquatic plants. We focussed on two practices: drying out ponds during a complete year after four years of fish production, and fish stocking with different densities. We used data collected in Dombes fishponds over the last 15 years. We monitored physico-chemical parameters of water and sediments, and abundance and richness of algae and aquatic plants. We also collected information on fish stocking levels and time since the last drying out. Our results show that the dry out year allowed a recolonization of aquatic plants during the first year with water, with levels of diversity and cover at their highest while the phytoplankton concentration is at its minimum. They are decreasing during the following wet years, in parallel with an increase in algae. Intermediate fish density levels also allowed the maintenance of numerous aquatic plant species, not found in more intensive systems. These two historical practices probably create intermediate levels of disturbances that contribute to maintain stable ecosystems, fish productivity and biodiversity.
Domaines
Biodiversité et EcologieOrigine | Fichiers produits par l'(les) auteur(s) |
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