A field survey of potential spawning sites for pikeperch (Sander lucioperca L.) - measurements of turbidity and other environmental parameters

The pikeperch or zander (Sander lucioperca, L) is a pelagic predator occurring in brackish and freshwater areas in Europe, with high economical and recreational values. The recruitment success is determined by several factors, out of which the most important are temperature and turbidity. Potential recruitment areas were surveyed in the field during the summer of 2012, by measuring environmental parameters consisting of temperature, salinity, conductivity, Secchi depth in seven bays (Ödkarbyviken, Saltviksfjärden, surrounding Sommarön, Ämnesviken, Slottssundet, Bodafjärden and Svartsmarafjärden) in the central part of Åland. The measurements were taken close to shore, and the sampling sites were located 300 to 500 metres apart from each other. An automatic temperature logger was placed in each of the bays on depths varying from 2.3 to 3.4 m. Turbidity was measured in the lab as NTU (Nephelometric Turbidity Unit). The potential recruitment areas were identified by further analyses on the turbidity using IDW-interpolations (inverse distance weighting) in ArcGIS, to construct maps depicting the turbidity in the bays studied. A higher turbidity value indicates a potential spawning site, as eutropication has a positive effect on the pikeperch and its recruitment success. The results indicate that potential recruitment areas can be found in the northern parts of Ödkarbyviken, Saltviksfjärden and Ämnesviken. Suitable sites can also be found in the southwestern parts surrounding Sommarön and the northern parts of Bodafjärden