effects of turbidity and zooplankton availability on the condition and prey selection of pike larvae

Along with increasing eutrophication the pike (Esox lucius) has decreased in numbers in some parts of the Baltic Sea. We undertook a field study to identify the environmental factors affecting condition of pike larvae around the southwestern coast of Finland. We also sampled the natural zooplankton community to reveal food preferences of pike larvae. Our mixed model showed that larval condition decreased with increasing turbidity, whereas temperature, salinity and stomach content were non-significant factors. One third of the variation in larval condition was explained by sampling site, indicating that site characteristics influenced the condition index significantly. The prey selection index showed that pike larvae preferred adult copepods and cladocerans, whereas they ignored rotifers and seemingly copepod nauplii as well. Together, our data show that food availability and several environmental factors are crucial for the condition of pike larvae, and probably also survival and recruitment.