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
Blue whale Naturae" of 1758, would have known this and may have intended the ironic double meaning. Herman Melville called this species "sulphur-bottom" in his novel "Moby-Dick" (1851) due to an orange-brown or yellow tinge on the underparts from diatom films on the skin. Other common names for the blue whale have included "Sibbald's rorqual" (after Sibbald, who first described the species), the "great blue whale" and the "great northern rorqual". These names have now fallen into disuse. The first known usage of the term "blue whale" was in Melville's "Moby-Dick", which only mentions it in passing and does not specifically attribute