Temporal variation in pond use and breeding success for ducks in French fishpond regions: on possible consequences of a decline in fish farming

Abstract

Key-words:fish farming decline, fishpond, duck population, habitat use, carrying capacityFish farming abandonment or extensification may theoretically lead to contrasting consequences for waterfowl breeding in fishpond complexes. We investigated the variation of four indices of duck density or breeding success in pond samples of three main French fishpond areas: Dombes, Forez and Brenne, along with recent changes in fish farming management. In Forez, where fish stocking has been frequently interrupted or fish biomass in ponds has substantially decreased during the two last decades, duck pair density strongly increased in the same time interval, but Mallard Anas platyrhynchos brood size decreased. In Brenne, no fish farming abandonment was observed but pond fertilization with organic manure or mineral nitrogen became less frequently implemented during the 2000s. The duck brood: pair ratio decreased meanwhile, indicating either a lower nesting success or higher losses before or immediately after hatching. In Dombes, lower fish stock densities since the 1990s did not reverse a negative trend in duck populations which started in the early 1980s. Our results suggest that fish biomass density in fishponds might be a limiting factor for breeding waterfowl, but a decrease in the nutrient level, for example with lower fertilizer inputs, may negatively affect duck reproductive success. RÉSUMÉVariation temporelle de l'utilisation des étangs et succès de reproduction des canards dans les régions françaises d'étangs piscicoles : sur les conséquences possibles d'un déclin de la pisciculture Mots-clés :déclin de la pisciculture, étang aquacole, population de canard, utilisation de l'habitat, capacité d'accueil L'abandon ou l'extensification de la pisciculture dans les régions d'étangs peut théoriquement s'accompagner de conséquences diverses pour l'avifaune aquatique. Nous avons étudié l'évolution de quatre indices décrivant la densité et les résultats de la reproduction des Anatidés sur des échantillons d'étangs de la Dombes, du Forez et de la Brenne, simultanément à une évolution des pratiques piscicoles. Dans le Forez, où de plus en plus d'étangs ne sont plus régulièrement empoissonnés et où la biomasse piscicole a fortement diminué au cours des deux dernières décennies, la densité des couples de canards a nettement augmenté,

Colony persistence in waterbirds is constrained by pond quality and land use

“…Although France's freshwater fish farm production is the largest in Europe (Barbe, Schlumberger & Bouretz, 2000), fish farming revenue has progressively declined over recent decades in Europe (Gomiero et al, 1997;Barbe et al, 2000). In contrast, revenue from waterbirds' hunting (mostly ducks, and not the black-headed gull, a protected species in France) has increased in fish farming areas in France leading pond management towards waterbirds attraction (Broyer et al, 2015). These opposite trends have driven a gradual change in pond management, and thus pond characteristics, as hunting practices do not require the same water levels and vegetation cover as fish farming.…”