Species hybridization between a female blue whale (Balaenoptera musculus) and a male fin whale (B. physalus): molecular and morphological documentation.

In 1986 a large, pregnant, female balaenopterid whale was caught in Icelandic waters. The animal had morphological characteristics of both the blue and the fin whale. Molecular analyses of the whale showed that it was a hybrid between a female blue whale and a male fin whale. The descent of the species hybrid was established without access to either parental specimen. Analysis of the fetus showed that it had a blue whale father. The present report of species hybridization between the two largest cetacean species, the blue and the fin whale, documents the occurrence of cetacean species hybridization in the wild. It is also the first example of any cetacean hybridization giving rise to a fertile offspring.