Boundaries

The rivers in the Gulf of Finland are excluded by the ecoregion’s south and southwest borders.  Together, the northern and westerly borders exclude the lakes of Karelian Lakeland [406].  The northern border also marks the divide between the Lake Onega basin and White Sea basin river catchments.  There are several channels and canals in the region—both natural and manmade—and the borders reflect historical conditions before large-scale human intervention.

Beloye [410] and Onega lakes are connected by the Volgo-Baltiyskiy Canal, and Lake Onega is artificially connected to the White Sea. The ecoregion’s southeastern border runs along the divide between the Volga catchment and Ladoga-Onega basin in the Vepsovskaya Upland.  The same border cuts through the Volkhov River, excluding the Ilmen Lake [404] in the Baltic Lowlands.

Topography

With a length of 1,570 km, a volume of 908 km³ and an area of 17,680 km², Lake Ladoga is not only the largest lake in Europe, but one of the largest in the world.  The quadrilateral lake widens in the south, and is marked by several small, skerry-like bays along its northern shoreline.  Islands dominate the northern coast, while rocky archipelagos—like the Valaam—take over in the south. The southeastern and southern coasts contain three large, open bays: Petrokrepost, Volkhovskaya Guba and Svirskaya Guba.  Despite the fact that Lake Ladoga plummets to 228 m in its deepest region, depths of roughly 100 m are more characteristic of the northern part of the lake.  The lake’s mean depth is 51 m, and it deepens with proximity to the southern shore, where the lake bottom evens out significantly.

Lodoga Lake is fed by three main tributaries—the Svir, Vuoksa, and Volkhov rivers— while the Neva River allows the lake to drain into the Baltic Sea.

Lake Onega is the second largest lake in Europe, with an area of 9,690 km². Its depth ranges from 30 to 120 m, and its three main tributaries—the Suna, Vodla, and Shuya rivers—keep its total volume around 292 km³. The Svir River connects Onega and Ladoga lakes.

Freshwater habitats

Both lakes contain deep waters that remain cold (1 to 4°C) year-round, yet the coastal waters heat relatively quickly during spring.  A distinct thermal bar between warm and cold water often separates water masses by roughly 20°C.  Despite unrelentingly cold temperatures in the lake’s central regions, cold-loving whitefishes and paliya still inhabit the areas during most of the year.

Terrestrial habitats

Both lakes’ shores appear particularly indented in the north. The southern shore of Lake Ladoga is extremely high and rocky.

Description of endemic fishes

There are two strict endemic species in the ecoregion: Salvelinus lepechini and Valaam whitefish(Coregonus baerii).

Valaam whitefish (Coregonus baerii)—a unique form of endemic whitefish—displays declining numbers, but still claims the highest growth rate among Lake Ladoga’s whitefishes. This species inhabits Lake Ladoga’s southern region, typically near estuaries of the rivers Volkhov and Svir. Lake Ladoga’s western and southern tributaries—the Syas, Pasha, and Svir rivers—once served as spawning grounds for the species. The Volkhov River was dammed in 1926, preventing C. baerii’s historic migration up the river to Lake Ilmen and its tributaries—the Msta (most popular spawning area on the way to Lake Mstina), Lovat, Pola, and Shelon rivers. Today, C. baerii exclusively inhabits the lower reaches of the Volkhov River. Commercial fishing on Lake Ladoga—which exploits C. baerii along with other lake whitefishes—looms as a threat to the species’ survival.

Coregonus lutokka—a near-endemic (and purportedly abundant) lake whitefish that lives in stony areas—embarks on an upstream summer migration in search of zooplankton. During this summer feeding session, large numbers of C. lutokka mass along the western, southern and eastern coasts Lake Ladoga’s southern half. During winter, the fish tend to gather along the eastern and western coats of the lake’s northern half.

Coregonus ladogae is also considered endemic in Lake Lodoga, though some scientists include the fish as part of C. albula. This proposed species differs from C. albula in spawning area size and other specific coloration and morphological features.

Coregonus kiletz is believed to be endemic to Lake Onega. It’s described as a large relative of C. albula, though—like C. ladogae—further research is required to confirm its status as a separate subspecies. Another subspecies of the Coregonus genus (name unavailable, but vernacular name is Ladozhskiy lake whitefish) may be one additional endemic subspecies, but further research is needed.

Other noteworthy fishes

Local fourhorn sculpin subspecies Triglopsis quadricornis onegensis (and one other possible unknown) appears to have marine origins, though these freshwater sculpins are smaller in size.  It’s known that the deep-dwelling fish maintain winter spawning patterns, though population sizes and other biological factors remain unclear.

Atlantic sturgeons have inhabited the Ladoga Lake basin since before the 19^th century.  This local lacustrine form once travelled up the Volkhov River for spawning, but purportedly never reached the Baltic Sea.  Some authors say the Baltic and Ladoga sturgeon specimens are actually the American Acipenser oxyrinchus, yet extremely scarce (and possibly locally extinct) remaining sturgeons make this difficult to confirm or reject.

Justification for delineation

Though, geographically, Ladoga and Onega lakes lie within the Neva drainage region (Baltic Sea basin), certain characteristics may warrant them a spot in a different ecoregion. Both lakes support several fishes and crustaceans that exist in large lakes of Sweden and North America.

As previously mentioned, the lakes are home to relict freshwater forms of the fourhorn sculpin—a species with marine origins. In general, the ecoregion supports unique fish fauna (which mostly share riverine ancestors of Atlantic-Baltic fish forms), whereas it completely lacks Siberian species and genera. Similar to the Barents Sea Drainages [407], this ecoregion formed postglacially and contains many forms of lacustrine whitefishes (Coregonus genus), making its reasons for delineation a bit more difficult to discern.

Level of taxonomic exploration

Relatively good, but of the taxonomic status of local Coregonus subspecies requires further study.