Mapping of possible spawning grounds for perch (Perca fluviatilis L.) and pike (Esox lucius L.) in Geta, Sund and Lemland, Åland Islands

A basic survey of potential spawning grounds for perch (Perca fluviatilis L.) and pike (Esox lucius L.) was conducted under the assignment by the Government of Åland during the summer 2010. The survey included inspection of both substrate, hydrography, vegetation and fish species. Totally 21 different areas were surveyed by seining, visual observations from the boat and snorkeling. Hydrography of the areas was studied by taking water samples from 0.5 m depth to determine salinity, water temperature and pH of the water; also Secchi-depth was measured at every location. A total of 24 and 34 different fish and vegetation species, respectively, were observed. 0+ perch was most abundant in Sund and Geta, supporting the hypothesis of these areas being spawning grounds of perch. In contrary, very little 0+ perch was caughed in Lemland, suggesting that this area is too exposed for spawning of the species. The overall catch of pike was too little to give sufficient background for conclusions on spawning grounds of this species. However, most of the locations in Sund and Geta had suitable vegetation, hydrography and water depth and could function as possible spawning grounds for pike. The survey method used was not appropriate for all study areas, and occasionally seining was impossible due to the typography of an area. Either underwater detonations, white plate -method and/or inspecting the amount of eggs during the springtime are recommended instead of seining or in addition to this method