Danube bleak by the building of dams across many of the rivers. Landlocked populations survive in small rivers and reservoirs, breeding in the small streams above the dams. The main Caspian Sea population has found ways of spawning below the dams. Overfishing and pollution in the Caspian Sea could impact on the Danube bleak but in 2008 the IUCN Red List of Threatened Species listed it as being of "Least concern". The Danube bleak feeds on small crustaceans, worms, molluscs, insect larvae, insects and small fish. Male Danube bleaks assemble in May to July at spawning sites in fast flowing streams with
Common minke whale in turn, was fathered by a North Atlantic common minke, demonstrating that back-crossing is possible between hybrids of the two species. The common minke whale is the smallest of the rorquals, and one of the smallest baleen whales (second smallest only to the Pygmy right whale). In the North Atlantic, Norwegian whaling vessels in 1940 allegedly caught individuals of up to in length, but they were likely only measured visually in comparison to objects of known dimensions aboard the ships themselves – the longest caught in subsequent years were typically only up to in length. In the North Pacific, Soviet