Common Pochard Aythya ferina breeding density and fishpond management in Central France
25 November 2019broyer, joël; bourguemestre, françois
Fishponds constitute a major breeding habitat for the Pochard Aythya ferina in Europe. This study explored possible causes of its recent decline, in describing the consequences of diverse pond management options in Brenne, central France. Pair density and the brood: pair ratio were described in a pond sample under varying management practices, in the early 2000s and, again, a decade later. The influence of pond management on these variables was studied by model comparisons. In the early 2000s, 69.5% of the studied ponds were fertilized by fish farmers. Higher Pochard pair densities were observed in those with artificial carp feeding and the brood: pair ratio was positively related to fish biomass density, provided that pair density was not too high. A decade later, only 25% of studied ponds remained fertilized. Pochard pair density was positively correlated with fish biomass density. But lower brood: pair ratios were recorded in ponds with artificial carp feeding, due to the fact that higher pair density there did not lead to increased brood density. Between the two study periods, the pair number remained stable in the sample but the brood: pair ratio decreased, from 0.84 to 0.71. Our results support the idea that habitat conditions that enable high fish productivity were also attractive for Pochard pairs. They suggest the hypothesis that pond fertilization for enhancing primary productivity and, thereby, fish biomass, may also favour Pochard breeding success. We must however bear in mind that, even with active fish farming management, fish biomass density in French fishponds remains usually moderate when compared to those in central Europe. The study did not reveal any effect of hunting management since waterfowl feeding, predator control or Mallard release did not significantly influence either pond use by Pochard pairs or the brood: pair ratio.