Ducks threatened by fish

Posted on June 4, 2011

Although ecological studies on fish and birds have a long history, many aspects of the ways in which birds and fish interact remain obscure.  For example, while it’s been noted that the breeding success of ducks is often poorer in lakes with large fish populations than those without fish, the reasons for this have been unclear.  Two alternative explanations are that fish compete with ducks for aquatic food, or that fish take ducklings as prey.  These possibilities were examined by comparing environmental conditions and invertebrate prey  populations in thirteen Swedish lakes containing fish (mainly pike and perch) with those in twelve fishless lakes.  The fishless state was due to low-oxygen conditions under the winter ice, or to periods of high acidity.  Lakes without fish supported higher abundances of invertebrate prey, more species of water birds, and higher rates of breeding success for two focal duck species (goldeneye and teal).   Because duck breeding success was better predicted by the presence of fish than by food abundance, it seemed likely that predation was more important than competition.  This study shows that the population dynamics of lake birds and fish can be inversely linked, which means that management designed to assist one group can disadvantage the other. 

Reference:  Elmerg, J., Dessborn, L. & Englund, G.  2010.  Presence of fish affects lake use and breeding success in ducks.  Hydrobiologia  641, 215–223.

Posted in: birds, fish, lakes