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Whitefish (Coregonus lavaretus) below and another whitefish species vendace (Coregonus albula) above. (Photo: Markus Vetemaa)
Whitefish inhabiting the Baltic Sea has two forms or subspecies: river-spawning and sea-spawning.

Due to the eutrpophication historical spawning grounds in the northern Baltic Sea became less and less suitable for whitefish. This fish has adapted to spawn in “crystal-clear” water on shallow sandy and gravel bottoms. A hundred years ago most of the small bays e.g. around Estonian big islands Saaremaa and Hiiumaa fulfilled this criteria. However, today these bays are often overgrown with algae. Sand bottoms are replaced with soft mud. Oxygen conditions are not perfect any more. Unfortunately, only few scattered bays can be still used by sea-spawning whitefishes.
Whitefish (Coregonus lavaretus)
Whitefish (Coregonus lavaretus) below and another whitefish species vendace (Coregonus albula) above. (Photo: Markus Vetemaa)