Mercredi 3 décembre à 10h, Lisa Dessborn, Doctorante (Universty of Kristianstad, Suède), présentera à la Tour du Valat un séminaire en anglais intitulé : « Impacts of fish on the breeding success of ducks ».
Hunting and fishing interests make some duck and fish species economically important. Time and money is put into increasing stocks by introducing both fish and ducks to wetlands, but little attention has been paid to the interactions between the two groups. It is generally accepted that fish can have great impact on invertebrate prey numbers, and fish introductions usually lead to a reduction in invertebrates. Newly hatched ducklings feed almost entirely on invertebrate prey during the first two weeks and this is also the time when they suffer the greatest mortality rates, often due to starvation. A reduction in available food is therefore likely to affect the survival rate of young ducklings and ultimately also affect recruitment.
Competition is one form of interaction between ducks and fish, but Pike, Esox lucius, may also predate on ducklings. Brood attacks have frequently been observed and ducklings have been found in the stomachs of pike, but the impact on survival and recruitment of the duck population is still largely unknown.
I will present the preliminary results of three studies:
i) An experimental study in Finland, using fish ponds with manipulated fish densities. Broods were added to the ponds, and behaviour and weights of ducklings were recorded.
ii) A descriptive study with a total of 25 lakes (12 with fish and 13 fishless) in boreal Sweden, examining natural patterns of breeding ducks.
iii) An experimental study based in boreal Sweden investigating the effects of pike introductions on breeding success.
The implications on the management of wetlands could be important if the presence of fish reduces the recruitment of ducks. Keeping some waters fishless could be a way of increasing recruitment and available game for hunting.