To assess the impact of predation by young-of-the-year (0+) fish on the population dynamics of Daphnia species, we made independent estimations of the mortality of Daphnia species during the year, and of the predation pressure exerted by the juvenile fish. Mortality of daphnids was computed using a model that allowed us to differentiate between different size- classes, while total fish consumption was estimated from the temperature-dependent daily weight increase and the population development of the 0+ fish. The predation pressure on the different size-classes of Daphnia species was estimated by combining the total fish consumption with estimates of the selective feeding behaviour of the fish. To make the estimates of fish consumption independent of our current (1989-1991) zooplankton data set, we estimated fish species-specific and fish length-dependent selectivity indices on zooplankton using a different data set (1976-1977). Daphnia population densities usually increased in spring and decreased rapidly in early summer. Predation by 0+ fish was not severe enough to explain the large mortality that caused the summer decline; later in the year most of the mortality in the larger size-classes of the daphnids (>1.0 mm) could be explained by fish predation. [KEYWORDS: Young yellow perch; clear-water phase; body size; planktivorous fish; leptodora-kindti; neusiedler-see; eutrophic lake; hyalina leydig; birth-rate; zooplankton]
Original languageEnglish
JournalCanadian Journal of Fisheries and Aquatic Sciences
Journal publication date1996

ID: 61401