Effects of lake restoration on breeding abundance of globally declining common pochard (Aythya ferina L.)

Relationships between breeding waterbird abundance, diversity, and clear water status after the restoration of two shallow nutrient‐rich Danish lakes

“…This includes directly increasing numbers of locally nesting pochard females, a huntable species of currently unfavourable conservation status that remains uncommon in Denmark. These results imply that a wider application of the restoration techniques described in this study has the potential to enhance breeding waterbird numbers and make a positive contribution to their flyway populations, especially for a species such as the pochard, which is showing flyway‐wide declines (Fox et al, ) but has shown positive responses to improvements in water clarity (Fox et al, ; this study).…”

“…the mute swan, Cygnus olor ). Such increases are expected, given the increases in submerged macrophytes in the relatively shallow waters of these lakes (Fox et al, ). They confirm results of earlier studies that show increased aquatic herbivore abundance in response to enhanced water clarity and submerged macrophytes at restored lakes (e.g.…”

“…However, the subsequent targeted and persistent removal of plankti‐benthivorous fish (such as bream and roach in Denmark) may sometimes be required to restore sufficient clarity to the water column in order to support the abundant development of submerged macrophytes (Jeppesen et al, ; Søndergaard et al, ). This has been the case at Søndersø Lake and Hejrede Lakes, with direct beneficial effects to one threatened species of breeding waterbird, the pochard (Fox et al, ). The results presented here show wider applicability to reflect the effects of improved water quality on the abundance, species richness, and diversity of the breeding waterbird community as a whole, which were associated with these lakes when they ultimately shifted from a turbid state to one of improved water clarity.…”

“…Breeding piscivorous waterbirds have also been shown to benefit from reduced sewage inflows and the restoration to clear water conditions at one shallow Mediterranean freshwater lake (Romo et al, ). Omnivorous dabbling ducks (the mallard Anas platyrhynchos , the Eurasian teal Anas crecca , the northern shoveler Anas clypeata , and the gadwall Anas strepera ) and diving ducks (the pochard and the tufted duck) have also benefitted from clear water conditions, especially at Søndersø Lake (Fox et al, ; Jørgensen, , ). The increases in the last two diving duck species are likely to reflect increases in their food supply at these lakes, especially because similar increases have been conspicuously absent at the adjacent Røgbølle Lake, where low nutrient loading and clear water conditions have been present throughout the period of restoration in the other two basins.…”

“…In an earlier analysis, Fox et al () showed increases in breeding abundance of a declining diving duck species (the pochard) associated with restoration programmes applied at two out of three separate nutrient‐rich shallow basins in the Maribo Lakes system on the island of Lolland, in southern Denmark (54°45′N, 11°32′E; Figure ). This analysis extends that study to test whether the annual breeding waterbird abundance, species richness, and diversity are related to total nitrogen or phosphorus concentrations or to water clarity in the same three lake basins.…”