Ilmast N.V., Sterligova O.P. Hydrobionts of the coastal zone in Lake Syamozero (South Karelia)

Institute of Biology KRC RAS, Russia 185910 Petrozavodsk, Pushkinskata str., 11; ilmast@karelia.ru

Lake Syamozero is a large part of the Onega Lake basin located in South Karelia and used for commercial fishing. The water surface area of the lake is about 260 km2. Seventeen rivers flow into the lake and one river, named Syapsya, flows out of it. The lake has a large littoral zone. Depths of up to 10 m make up over 76%, depths of 10 to 18 m 21% and depths over 18 m 3% of the lake area. There are rocky, sandy, muddy, ore and clayey types of bottom deposits in the lake. Muds make up about 60% of the bottom. The total catches in the surface and bottom layers being practically equal, catches per fishing effort at these stations differed by one order of magnitude. A higher fish density, recorded in the epilimnion, reflects a higher productivity in the surface layers of the lake, where the main food resources of plankton-eating fish are concentrated. The spatial distribution of fish in the epilimnion shows a biotopic heterogeneity in this zone; in shoals (in the littoral zone) and in deep water sectors fish density increases. In the hypolimnic layer fish density typically rises with a decrease in depth. The populations of different (bottom and surface) zones seem to be relatively isolated. Size segregation is observed in species capable of forming environmental forms, such as perch and roach, and in predatory fish. The presence of size segregation suggests a difference in environmental preferendum in fishes that inhabit different limnic zones.