Utilization of natural and artificial habitats by YOY pike in a biomanipulated lake

Biomanipulation by stocking with YOY pike Esox lucius has been shown to be a useful tool in the restoration of shallow hypertrophic lakes. The success of such stocking depends partly on the standing stock of the YOY pike in t he first 2-3 months following stocking, this in turn depending on habitat t ype and abundance in the lake. The present study evaluated the general habi tat use and preferences of YOY pike and the suitability of artificial subme rged habitats formed by small laid out spruce trees Picea omorica using Poi nt Abundance Sampling by Electrofishing (PASE). This sampling method was as sessed as being suitable for catching and quantifying small pike. While ver y few pike were present in either the dominant emergent vegetation Phragmit es australis or the subdominant vegetation Typha spp. in June and July, the y were present in significantly greater numbers in the artificial habitats. This suggests that the use of spruce trees as artificial habitats in bioma nipulation projects could potentially enhance the standing stock of YOY pik e. In August, in contrast, habitat utilization by the YOY pike did not diff er from that expected if they used the habitats randomly. This suggests tha t YOY pike change their habitat utilization as a function of their size. Th us they use habitats with a complex structure in the early summer, but in l ate summer when they are larger, they use habitats with a less complex stru cture such as Phragmites and Typha.