Reproduction of pike (Esox lucius) in reed belt shores of the SW coast of Finland, Baltic Sea : a new survey approach

The coastal reproduction areas of pike in the western Gulf of Finland were surveyed during spring 2004 and 2005 using a new approach. The locations of reed belts, the most important spawning substratum, were first identified using aerial photos, and 36 sites in three archipelago zones were selected for field sampling. The occurrence of pike larvae at each 100 m long site was observed with the aid of a white plate and a scoop. The majority of pike larvae were found in a habitat formed by the previous season's flattened reeds at a water depth of 20-80 cm. The comparison between archipelago zones revealed that reed belt shores in the innermost archipelago and bay area, substantially influenced by freshwater inputs in the spring, are the key reproduction areas of pike. Pike larvae were abundant in these areas, in contrast to the intermediate and outer archipelago, where pike larvae were found only sporadically. It is likely that productive habitats in the inner archipelago serve as a source and the outer archipelago as a sink, the latter maintaining pike population with the aid of juvenile immigrants from the main reproduction areas. The results also indicate that pike can not take full advantage of the slowly increasing spatial coverage of reed belts in the intermediate and outer archipelago of the western Gulf of Finland.